; ■ ! :; '■>' ■■■ I jfii -j a , ; ; ; . , 1X11.13 ■i P Rw mffl II sill Hi I tlftna illl i^Hl II liHIinWninTlffl liBliM H II HIS m iaiuil „J^Hfl MM— W BHflMMBH ■HHH HI SHE MMfifflflWMl Iffliiillil' HiillllSHS finffna RW8 WflffmS ram MffiBHl Book G-^t GopiglitN . r\ COPYRIGHT DEPOSIT. MACHINE DRAWING A PRACTICAL GUIDE TO THE STANDARD METHODS OF GRAPHICAL REPRESENTATION OF MACHINES, INCLUDING COMPLETE DETAIL DRAWINGS OF A DUPLEX PUMP AND OF A DIRECT-CURRENT GENERATOR By CHARLES L. GRIFFIN, S.B. ASSISTANT ENGINEER, THE SOLVAY PROCESS COMPANY AMERICAN SOCIETY OP MECHANICAL ENGINEERS AND C. C. ADAMS, B.S. SWITCHBOARD ENGINEER WITH GENERAL ELECTRIC COMPANY ILLUSTRATED AMERICAN TECHNICAL SOCIETY CHICAGO 1920 1° <% % . ^° COPYRIGHT, 1914, 1920, BY AMERICAN TECHNICAL SOCIETY COPYRIGHTED IN GREAT BRITAIN ALL, RIGHTS RESERVED : ¥ MAY l3i92(T )CU565943 CONTENTS PAGE Working drawings 1 Definition of 1 Lines 2 Arrangement of views 4 Sectional views 5 Shade lines 7 Dimensions 9 Classes of Workmen using drawings 11 Specifications for screw threads 15 Specifications for bolts and nuts 20 Specifications for pipes and pipe threads 26 Scale drawings 27 Details of preparation 31 Pencil drawing 31 Tracing 32 Blue printing 33 Illustrative drawings 37 Crank 37 Bell crank 41 Rocker arm and pin 42 Link stud 43 Flange coupling ' . . 43 Clamp eye 45 Connecting rod 4G Gear with split hub 46 Spur gear 49 Pair of beveled gears 49 Worm and worm gear 49 Cylinder head 52 Water cylinder for triplex pump 53 Hoisting drum 56 Crane drum grooved for chain 56 Detail of ordinary shaft 59 "Broken" pieces and "out-of-scale" dimensions 60 Bearing stand with cap and boxes removed 60 2 CONTENTS PAGE Working drawings Sample letters 61 Drawing room practice 62 Plates 63 Mechanism drawing 69 Helix 70 Screw threads 75 Cams , 82 Belting 108 Gears 132 Plates 14a Working shop drawings— mechanical 157 Plan and scope of advanced work 157 Essential requirements 159 Duplex pump plates 163 Steam end layout 165 Steam cylinder 171 Piston rod and valve stem 184 Steam chest and valve 186 Valve motion layout 189 Valve motion details 193 Yoke, stuffing boxes, bracket, etc 195 Water end layout. 199 Water cylinder 201 Water cylinder cap and air chamber '. 204 Plunger and valve details 206 Foundation 208 General drawing 208 Order sheets 211 Shop drawings — electrical. 219 Requirements 219 Essentials of a good drawing 220 Design of a direct-current generator 222 Material supplied to designing draftsman 222 Preliminary layout sketch 224 General outline drawing 224 CONTENTS 3 PAGE Design of a direct-current generator Details of armature and commutator -. 224 Armature punchings 226 Armature windings 226 Armature flanges and spider 230 Equalizer rings and support 231 Commutator details 233 Armature shaft 238 Details of field frame and coils 238 Magnet frame and base 240 Pole pieces 241 Main field coils and spools 245 Commutating field coils and spools 246 Details of brush rigging. 249 Brush holder, stud and connections 249 Brush holder yoke and brush shifting device 253 Bearings and pedestals 255 Split bearings for armature shaft 255 Pedestals and caps for bearings 257 Details of electrical connections ■. 259 Assembly of connections 259 Connections 262 Final assembly drawing 262 Outline 262 p w H S tt> Pi o H < « w a fc 5 w a o a. s p Si H •*> i. 8 9 ^j 1 * * w ■a (X ^ o c « w 1* « w w 09 £s P V O 3 a ,e HH H W b K O H b w to O INTRODUCTION r I J HE ability to visualize a piece of machinery, to arrive at ■*■ the exact idea of the designer or the inventor, and then to draw these details in such a clear and concise form as to make them thoroughly understood is a very important attribute in the manufacturing world. The pattern maker must have just the views and dimensions of the machine that will enable him to make accurate patterns for the cast parts. The shopman must be furnished with every detail which he should know in order to finish the pieces to proper dimensions; he must be told just what surfaces to leave rough, which ones to machine in the lathe, and which ones to caliper to thousandths of an inch. It is evident, that the machine draftsman who is to do his work with the highest efficiency must not only be able to draw accurately, but he must thoroughly understand the machines which he is called upon to represent. <& To one who understands "reading drawings", a well-made set of specifications is really a work of art, and it is the aim of the publishers of this little volume to put in the hands of those who are only moderately schooled in the art of mechanical drawing the means of developing themselves in the broader art of machine drawing. The subject has been developed very logically, starting first with the presentation of the details and the conventional ways of representing the parts of simple machines, followed by standard methods of working out such mechanisms as screws, pulleys, cams, gears, etc. Finally, complete detailed drawings are furnished and exhaustively discussed in connection with the designs of a duplex pump and of a direct-current generator. The presentation is exceedingly practical and will appeal to men who are interested in either the mechanical or electrical fields. The plates are complete in themselves, but if a person wishes to obtain the maximum benefit from his study he may work out enlarged drawings to scale without any additional details. GISHOLT TOOL GRINDER Courtesy of Gisholt Machine Company, Madison. Wisconsin MACHINE DRAWING PART I WORKING DRAWINGS METHODS AND CONVENTIONS In Mechanical Drawing, Parts I, II, and III, the common drafting instruments and materials are described, and hints given regarding their use ; the fundamental geometrical problems are solved ; the principles of orthographic projection are stated, and their appli- cation to intersections and developments illustrated. A careful study of these Parts, with the actual drawing work incident thereto, should have given the student considerable facility in producing good line work; he should now be able to draw neatly and accurately any simple piece which may be given him, correctly applying the principles as described. In producing working drawings the principles already laid down are constantly used, and the more they are at the finger ends of the student the easier his work will become. The principles of projection must be thoroughly understood and fixed in the student's mind in order that he may devote himself with the greatest applica- tion to the actual detail of the drawing, and he must not be com- pelled at every step to turn back to find out how to make the simple projections. Definition of Working Drawings. A working drawing is a drawing which completely instructs the workman, so that he is able actually to make in the shop the object which the drawing repre- sents; in other words, a working drawing conveys to the mechanic all the information necessary to make the object. The student should constantly keep before him the idea that the workman must take a drawing, and, without any further instructions verbal or written, produce the object as the draftsman intended it to be made. The instruction supplied by the drawing should not only cover the form and size of the object, but also the kind of material of which it is to be made, the number of pieces desired, and the 2 MACHINE DRAWING finish of its surfaces. A drawing, therefore, is a sort of abbreviated language, or shorthand method of conveying an amount of exact, detail information, which it would take many pages of manuscript to convey. A second point to be noted in connection with a working draw- ing is that the workman has no time to puzzle over a mass of lines and figures more complicated than necessary. This means that special attention must be paid to making the drawing as simple as possible; all lines and figures which are unnecessary, beyond the point of conveying complete information, are hindrances rather than helps to the workman; moreover, it takes the draftsman's time to make these extra lines and figures, and thus the drawing FULL LINE FOR GENERAL DRAWING. FULL LINE FOR "DETAIL DRA WING. DOTTED LINES FOR INVISIBLE PARTS. ■ CENTER LINE. .DIMENSION AND EXTENSION L INES. " (USE E/TNER) SHADE LINES. Fig. 1. Conventional Lines Used in Machine Drawings becomes unnecessarily expensive. A good drawing, therefore, not only implies accuracy and completeness but also simplicity and direct- ness. Lines. The secret of a clear drawing, as far as the line work is concerned, lies not only in absolute uniformity in the making of the lines, but in choosing certain characteristic lines to convey differ- ent ideas. The most common kinds of lines used are shown in Fig. 1 and described below, and the purposes of their use are stated. Full Lines. Full lines represent the portions of the object which are visible; they should be bold and clear, heavy on detail drawings, say & " wide, and lighter on an assembled drawing. Invisible Lines. Invisible lines represent the hidden parts of the object; they consist of short dashes regularly spaced, the spaces MACHINE DRAWING 3 being about \ the length of the dash ; the dashes should never have a greater width than that of the full line, and usually should be slightly less. A drawing is much easier to read if the full lines force themselves on the eye, while the dotted lines, by their lighter char- acter, are left in the background. Center or- Axis Lines. Center or axis lines consist of alternate long and short dashes, finer than the main lines of the drawing. Fig. 2. Flanged Coupling Giving Practical Application of Fig. 1 Some draftsmen prefer not to use "dash and dot" center lines, but make them continuous fine lines. Either style is good. Dimension and Extension Lines. Dimension and extension lines are made fine, like center lines, and may be either full or dotted, according to the preference of the draftsman; the full line is prefer- able on account of its bolder character and the shorter time it takes to make it. Extension lines start a short distance away from the edges of the object, so as to break up the continuity of the lines of the object and the extension line. Dimension lines are run between the extension lines, terminating at the extension lines in arrows. The extension lines should always run a short distance beyond the point at which the dimension line touches them. 4< MACHINE DRAWING Shade Lines. Shade lines are used for the purpose of more clearly bringing out to the eye the projecting edges of the object on the shadow side, and should be the heaviest lines on the drawing; the proper effect is secured if these lines are made nearly twice as heavy as the principal lines of the drawing. Fig. 2 shows a flanged coupling in which the lines given in Fig. 1 are applied to an actual problem. In the lower half of the elevation observe how the invisible parts are shown by dotted lines. Arrangement of Views. Imagine a rectangular block placed within a glass box, and the surfaces projected to the top, front and right-hand side, as in Fig. 3; now open the box in the manner indi- cated in Fig. 4 and we have three views of the object on a plane surface, i.e., the drawing paper of the draftsman. These views are called top plan, front, and side elevations respectively, and are denoted in the figure by the let- ters T, F, and S. If more views are required, the arrangement is shown in Fig. 5. The bottom plan B is found below the front elevation, and the left side eleva- tion S f is found on the left of the front elevation, the same princi- ples of projection being used as in the former case. The above procedure is equivalent to tracing on each side of the box the outline of the ob- ject as observed by the eye, when directly in front of each side of the object; after this is done the unfolding of the box results in the outlines shown in Fig. 4. If we consider the front ele- vation of the object as our starting point, then the top plan is above, the bottom plan beloiv, the view of the right-hand side is on the Fig. 3. Rectangular Block Within a Glass Box, the Surfaces Projected to the Top, Front, and Right-Hand Side Fig. 4. First and Preferred Method of Show- ing Top, Front, and Right-Hand Side Views of a Rectangular Block on a Plane Surface MACHINE DRAWING r B Fig. 5. Method of Showing Five Views of a Rectangular Block on a Plane Surface right of, and the view of the left-hand side is on the left of the front elevation. This arrangement of views is easily remembered and is very logical; it is the most common method of projection in drafting work, and will be used throughout this book. For such a simple object as that considered above, two views only are necessary, a front elevation and top plan, but machine drawings frequently require three views, top, front, and side, and sometimes more. Some draftsmen prefer the method of projection shown in Fig. 6, by which the lines of the object, instead of being observed through an imaginary glass parti- tion and traced thereon, are pro- jected away from the eye upon surfaces beyond the object; the surfaces are then unfolded as be- fore, with the result, as shown in Fig. 7, that the front elevation, being the starting point, the top plan is below, the bottom plan is above, the left-hand view is at the right of, and the right-hand view is at the left of the front elevation. This system of projection has few advantages for machine drawing, and has been largely superseded by the former method. Sectional Views. The inte- rior construction of machine parts, especially if at all compli- cated, can seldom be clearly or completely shown by dotted lines. A large number of dotted lines on a drawing is very con- fusing, and in many cases ren- ders the drawing useless. Sec- tional views are used to over- come this difficulty, and as an unlimited number of sections can be taken, it is always possi- ble to make clear the interior construction of any piece, however complicated. Fig. 6. Second Method of Showing an Object and Its Projections in Vertical and Horizontal Planes {Not Advised for Machine Drawing) 6 MACHINE DRAWING Crosshatching. To make a sectional view, the object is supposed to be cut open, and all the material removed between the cutting plane and the eye. This makes visible the hidden portion, and the drawing, therefore, consists of full lines made the same as any other, except that the material which was cut by the plane is "cross- hatched". Crosshatching consists of drawing medium width lines, regularly spaced, across the cut surface, the lines usually being at an angle of 45° with the horizontal. In case of two adjoining sur- faces being cut, the lines are sloped to the right and left, respectively. The butt joint given in Fig. 8 shows the use of crosshatching when the section taken is through different pieces of the same mate- FRONT ELEVATION H TOP PLAN Fig. 7. Second Method of Projection, Planes Unfolding {Not Advised for Machine Drawing) Fig. 8. Butt Joint Showing Use of Cross- hatching When Section Is Through Differ- ent Pieces of One Material rial. Notice the different angles at which the section lines are drawn for each separate piece. It is often convenient to show the kind of material of the object by the style of crosshatching. The conventional styles generally used are illustrated in Fig. 9. It is quite general, however, to use the plain form (as for cast iron), and call for the material by a specific note, thus leaving no possible doubt of the material required, and simplifying the labor of crosshatching, which is a tedious process at best. The distance between the lines should be as wide as possible, MACHINE DRAWING to save labor, and yet bring out the surface clearly. A good average spacing is about ■£%". Fig. 10 shows the end of a connecting rod. The section shows the different materials of which the object is made, cast iron, brass, steel, and babbitt. cast iron WROUGHT IRON. STEEL CQMPOR SRASS WW %W% Wm vV//// LEAD OR BABBIT WLCAN/TE moo BRICK Fig. 9. Conventional Representation of Materials Shade Lines. The theoretical principles for shade lines, already given in Mechanical Drawing, Part III, cannot be exactly applied to working machine drawings without involving an excessive amount of time and labor. The conventional rule, therefore, has been Fig. 10. End of Connecting Rod Showing Crosshatching When Section Is Through Different Materials established that shade lines may be used for all lower and right-hand projecting edges. By "projecting edges" are meant edges of surfaces which are not flush with adjoining surfaces, but which project above them, or are in a plane nearer the eye. All views of an object are s MACHINE DRAWING Fig. 11. Direction of Light Rays and Loca- tion of Shade Lines treated alike, the ray of light casting the shadow being supposed to come from the upper left-hand corner of the drawing. The contour lines of cylinders, cones, and other rounded surfaces, if projecting, are shaded the same as sharp edges. Uses. Shade lines, when used, are for the specific purpose of relieving the flatness of draw- ing, and represent a purely con- ventional means of indicating to the eye projecting surfaces, i.e., surfaces which are in different planes parallel to the eye. Whether the surfaces be curved or flat, as long as they are pro- jecting, or in front of other surfaces, is of no moment, for the effect desired is the same for both, namely, the separation of the surfaces. Applications in Practical Work. Few drawing offices allow shade lines to be used on regular detail machine work on account of the extra labor required and the loss of accuracy in the drawing by the use of a wide line. For general or "show" drawings, where the I effect of separating the surfaces is desired, thus bringing out more clearly the relation of the parts, the use of shade lines is occasion- ally permitted. The draftsman should know how to apply them when required, and Figs. 11 to 16 illustrate their use. S hade- Line Methods . Fig . 1 1 shows the assumed direction of the ray of light in each of the three views. The piece should be inked in with the usual standard width of line, then gone over the second time, making the extra width for the shaded lines on the inside of the proper lines. This leaves the outside measurement of the piece unchanged for possible Fig. 12. Location of Shade Lines for Piece with Hole MACHINE DRAWING 9 scaling. Some draftsmen claim that they can make the heavy shade lines as they go along, thus avoiding the second inking, but in the long run it will be found that time will be saved, more uniform lines and fewer blots made, if the process of shading be accom- plished by a second inking. Fig. 12 is similar to Fig. 11 but with a hole instead of a lug, and the difference in shade lines should be noted. Fig. 13 is the same as Fig. 11 with a round boss and the lower right-hand corner rounded. Fig. 14 is a plain washer, Fig. 15 a common hexagonal nut. Fig. 16 is a washer or disk with a shaft in it. The right- and left-hand views are shown to bring out the point that the shaft projecting on the right has its end shaded, while on the left, being flush with the face of the disk, it is not shaded. Fig. 13. Location of Shade Lines for Rounded Corner Fig. 14. Location of Shade Lines for Circular Piece r Fig. 15. Location of Shade Lines for Hexagonal Piece Dimensions. It is easy to spoil an otherwise good drawing by loose and careless methods of putting on dimensions. Systematic and careful effort must constantly be used to make every dimension 10 MACHINE DRAWING upon a drawing absolutely clear. To put it still more strongly, it must be absolutely impossible for any dimension of a drawing to raise doubt in the workman's mind as to its meaning. The drafts- man has no justifiable excuse for mistakes in the shop due to poorly made dimension lines or small and blotted figures. The arrows terminating the dimension lines should be pointed, bold, and regular, thus, (- — j/' *|, not like this, K — &f- — H. The arrow points should exactly touch the extension lines, thus, \* — &£ — *4, not like this, H — ^^ * I'c'Bozs Fig. 31. Preliminary Sketch of Crank be located by the figure 2§" to its center, its location in the other direction being on the center line of the arm. This boss has a diameter of 2f " and a length of 2i" each side of the center to the finished surface, the depth of the counterbore being T V \ an d the width of the slot to the bore \" 3 all of which dimensions should be carefully put on. The boss has a hole in it tapped at one end for a 1" bolt and drilled at the other end \h" - This completes the figur- ing of the large hub and we can proceed to dimension the other end of the arm. This has a diameter of 4f ", the thickness of the arm being 2", and there are facing pads on either side \" high, bringing MACHINE DRAWING 39 the total distance from face to face 2J"; in order to show positively that these portions are central with the faces of the large hub, the figure \" is put at one side; the diameter of these facing pads is 3J", and the hole through the head of the crank is \\\ " diameter. Having put on the above figures we now have to provide a connection be- tween the head of the crank and the hub, and it therefore becomes necessary to give figures, for the size of the arm; the thickness of the arm has been already given as 2", and the width being the same as the diameter of the hub, the side lines are simply drawn tangent to the same; at the smaller end the width may be conveniently given along a line tangent to the facing pad as 3|". The arm is filleted into the hub by 1" radius. The only thing now uncertain is whether the corners of the arm are sharp or rounded, and this is shown by the little section of the corner giving \ " radius. The above description is tedious and the dimensions can prob- ably be put on more quickly than the discussion of them can be read, but it should be especially noted that the systematic method has been followed of taking each part of the piece separately and dimensioning it before taking up any other part. While this is not always entirely possible to do in complicated pieces, yet it is absolutely necessary that in general this principle be always fol- lowed; otherwise it is impossible to be sure that all dimensions are on. The description above also applies to the dimensioning of the piece after it is drawn in detail, this being represented in Fig. 32. Referring to this figure, the bold character of the drawing should be noted, the solid lines being strong and of absolutely different character from the center or dimension lines. There is no uncer- tainty about the direction or termination of the lines; the figures are bold, plainly made, and absolutely clear; there can be no possible excuse for the workman to read any of the lines or dimensions wrongly. In other words, the drawing satisfies the definition of a working drawing, as previously given, in that it conveys absolutely definite instructions to the workman, expressed in the simplest and most straightforward way. Finished Drawing. On most machine parts a portion only of the surfaces are finished; and these are usually indicated, as previ- ously noted, by the small letter / placed across the line representing 40 MACHINE DRAWING the surface; this indicates to the pattern maker that he is to allow extra stock on the pattern, so that when the rough casting is made there will be sufficient metal to enable the finishing cut to be taken to the proper dimension. These finished surfaces are the most important surfaces of the piece, to which all the other parts have to be related. In order that the several parts of the machine may properly go together, it is necessary for the draftsman, in putting on the figures, to start from some one finished surface, and so arrange 1 1^ DRILL C'BORE Fig. 32. Detail Drawing of Crank the figures that the machinist can readily work from one finished surface to another. In Fig. 32 the dimensions of the rough parts as given may not be exactly maintained in the casting, but the distances between the finished surfaces must be exactly secured. The method of figuring a keyway is illustrated in this figure, and it should be carefully noted that the depth of the keyway ( iVO is given from the corner where the side of the keyway intersects the bore; this is because the depth of the keyway is readily measured by scale from this point. The thread for the 1" bolt is indicated in this case by a double line, the inside line representing the bottom, the outside representing MACHINE DRAWING 41 the top of the thread, while the lines of the helix are entirely omitted. This is not as common a method of representing a thread as the conventional method previously described. Bell Crank. Fig. 33 shows a bell crank fastened to its shaft by means of a set screw, the same general features being noted in this as in the preceding figure. A further point is the method of express- ing the distance between the faces of the principal hub and the smaller hub, "10" less -fa" ". This method of stating a dimension is quite common among certain manufacturers, as it saves giving odd dimensions and conveys more quickly to the workman's mind what BELL CRANK ON£-G.I . Fig. 33. Method of Showing Dimensions on Detail Drawing the dimension is. The other method of stating this would be "9 ft * ", which is obviously a somewhat cumbersome and odd dimension; it is easier for the machinist to read 10" on his scale and finish the distance ^ " less, than it is to use the actual figure. This point is an instance in which the instructions furnished by the drawing to the workman are simplified for his benefit. Another point worth noting in this figure is that circles are dimensioned by giving the diameters in preference to the radii; this is for the benefit of the pattern maker and the machinist, who always use calipers for measuring these parts. When the radii are given, the workman is forced to multiply the radius by two in order to secure the dimension for his calipers; and it is always better to 42 MACHINE DRAWING remove the chance of error on the part of the workman in the shop when making mathematical calculations. A detailed drawing should be so completely dimensioned that there will be no occasion for the workman to make any calculations himself; for, even if he is com- petent to do it, the responsibility for the correctness of the figures should be on the draftsman. In practically all shops the workmen are not allowed to scale the drawings in case dimensions are lacking, but are required to go to the drafting room and have further dimen- sions put on as required. A good detail drawing should require no such additions. ROCKER ARM PJN ONE- C.ff.s. Fig. 34. Detail of Rocker Arm and Pin Rocker Arm and Pin. Fig. 34 shows the detail of a rocker arm and pin, such as are frequently found in connection with the valve gear of a steam engine. This is a case where it is just as clear to detail two pieces together as to separate them entirely, the rocker arm pin being shown in position in the large hub and dimensioned in that position. This is not only simpler, but it gives the added information to the workman of just how the pin goes in the arm, and enables him to make his fits accordingly. MACHINE DRAWING 43 This principle of detailing several pieces together may, however, be carried to the point where the drawing becomes confused and complicated; then it is best to separate the detail of the parts. There are often special reasons requiring the detailing of parts of one kind on one sheet and of another kind on another sheet? for example, some shops detail forgings on one sheet, castings on another, parts to be made on the screw machine on another, and turret lathe work on another, etc. Such arrangements are, however, dependent upon the particular shop organization to which they apply. Link Stud. Fig. 35 shows a link stud, also used in connection with the valve gear of an engine. On such pieces as this it is usually considered that they are finished all over unless otherwise mentioned. It is always desirable, in finished pieces of this character, to give T _ the length over-all of the pieces, ^ - 2" AC ROSS FLATS 3" f6* u 31 i •f -r LINK STUD TWO STEEL Fig. 35. Detail Drawing of Link Stud in order that the workman may quickly determine how much stock to order from the stock room without having to add up the figures between the various shoulders of the piece. The head of this stud is a hexagon, and the usual method of calling for the hexagon is given in the note, "2" across flats". The reason the dis- tance across flats is specified is to enable the workman to see at once what the necessary width of the jaws of the wrench must be in order to fit the head of the stud. Flange Coupling. Fig. 36 shows a flange coupling such as would be used to connect up a line shaft in a shop, or any heavy machinery shafting. The detail construction of this is most clearly shown by making the drawing in cross section. This drawing is a good illustration of the placing of the dimensions entirely outside the lines of the drawing, thus enabling any changes to be made in the figures without in any way obliterating the drawing. It also keeps both drawing and figures definite and clear, avoiding any possibility of confusion. Each half of the coupling is fastened to its shaft by a tapered key; and in order that it may be clearly under- stood which way the top of the keyway is tapered, the arrows, \ 44 MACHINE DRAWING shown in the cross-sectional view, indicate the direction in which the key is driven home. Pattern Numbers. On this drawing are indicated the pattern numbers. They would be equally necessary on all other castings illustrated in this book; but for purposes of simplicity they have generally been omitted. Pattern numbers are necessary, not only that the patterns may be filed away systematically, and readily found when wanted, but also that the necessary orders for the cast- ings may be written, and that the pieces may be identified on the drawings. For wrought-iron and steel pieces which have no patterns, MSC6 2% Flange Coupling - Steel Casting 2 - remale - MSC 6. Ship with shcrff MS/7. 2- Male - MSC<5. • * * "f&S. Fig. 36. Detail Drawing of a Coupling, Using a Cross-Sectional View certain letters or numbers are given them, such that the identifica- tion is as complete as with castings. Castings, whenever possible, carry on their surface the pattern numbers in raised figures, and when received in the shop or field can thus be identified for assem- bling in the machine. Wrought-iron and steel pieces, which cannot have such figures raised upon them, are usually marked with painted letters and figures, to correspond with piece marks called for on the drawing, thus enabling them to be properly identified at the shop and in the field. There are many different systems in vogue for this numbering, dependent upon the particular requirements of the shop organization to which it applies. MACHINE DRAWING 45 Clamp Eye. Fig. 37 shows a piece designed to receive a threaded Tod at one end and to clamp rigidly to a shaft by means of a bolt at the other. This detail, simple as it appears, is awkward to make, on account of the bolt boss being at an angle with the principal center lines. The lower view is a cross section, because, if the ordinary elevation were shown, it would have a series of ellipses showing the bolt boss projections. It is always desirable to avoid oblique projections of circular shapes on account of the difficulty of drawing same; moreover, the ellipses 'produced do not show the Fig. 37. Detail Drawing with a Projection Thrown Off at an Angle with the Principal Center Lines construction as plainly as a straight projection. The method adopted in such cases is to throw off a straight projection at the same angle as the part in question makes with the principal center lines. In the present instance it is necessary to show that the boss for the bolt is f" radius, and that the boss is centrally located with the hub, which is readily done by the straight projection thrown off. In the cross-sectional view, the lines representing the thread appear to the eye sloped in the wrong direction, or as though the thread were left-hand. A moment's thought, however, will convince the student that, since the section taken is through the middle of the hole, we are merely looking at the back side of the hole, and that the threads of a right handed screw on the back side must neces- sarily slope in the direction as shown. In the case of the thread on 46 MACHINE DRAWING the bolt for the clamping hub, shown dotted, the lines of the thread appear right-handed to the eye, it being universal practice in the case of dotted threads to show the side only next the eye. If the threads on the back side of the bolt were also shown, they would slope in the other direction, crossing the other lines, and to draw them in would obviously cause confusion. Connecting Rod. Fig. 38 shows the connecting rod for a small steam engine. This piece calls for little comment. The outlines of the crank pin and cross-head pin are shown in dot-and-dash circles, and the relation of these centers to the rod is given. This is of some importance in enabling the detail of the boxes, which go in the heads of the connecting rod, to be correctly detailed and checked. It Fig. 3S. Detail of a Connecting Rod should be carefully noted by the student, that any such information which can be given on the details, without confusing the drawing, to tie up one detail with another, is usually good practice. It not only saves time in the drafting room in checking and general refer- ence work, but it gives the workman a better idea of how the parts are expected to go together, thus fulfilling the general definition of a working drawing as "complete and definite instruction". Gear with Split Hub. Conventional Drawing. Fig. 39 shows a gear with a split hub, the bolts through the hub being for the pur- pose of tightly clamping same to the shaft. This is an illustration of the conventional method of showing a gear with standard propor- tions of teeth. If the drawing were made exactly as the gear would look, it would be necessary to spend a large amount of time inking in the outlines of the 72 teeth around the circumference of the gear; MACHINE DRAWING 47 instead of doing this, the pitch line of the gear is shown, and circles drawn indicating the top and bottom of the teeth. The pitch diameter and outside diameter are given, and the proper depth of tooth cut to be made by the gear cutter; nothing more is necessary. GEAR CUT 72T.-1.D.P. INVOLUTE: ONE- C. /. Fig. 39. Detail of Gear with Split Hub The information which enables the workman to choose the proper cutter is given in the title; thus, "Cut 72 Teeth — 1 Diametral Pitch — Involute." The workman will receive from the tool room a stand- ard involute cutter marked for 72 teeth, 1 diametral pitch. After placing same on the arbor of the gear-cutting machine, he will drop the cutter into the gear blank to the depth called for by the drawing; 48 MACHINE DRAWING if this is accurately done, it will give the desired standard thickness and clearance of the teeth, and the automatic indexing of the machine will produce the 72 teeth, accurately spaced. If the gear were a cast gear — in which case the pattern maker would have to lay out the teeth and finish them one by one on the pattern — it would be necessary to draw one or two teeth on the circumference of the gear, Fig. 40. Detail of Gear with Solid Hub and give sufficient figures to enable him to lay out the teeth either by his dividers or by a template. In neither case, however, should the detail draftsman take the time to draw the teeth in any great number around the circumference of the gear; this is a very common thing for the young draftsman to do, and nothing shows his green- ness more. He should bear in mind that when the proper instruction has been conveyed by his drawing, any more time spent on it is wasteful. Cross Section. The cross section of the gear is shown to enable the necessary figures to be placed upon the rim and hub. In the MACHINE DRAWING 49 right-hand view, only one-half the complete circle of the gear is shown; nothing would be gained by showing the other half, therefore it would be a waste of time and space on the drawing to make it. Attention is called to the method of indicating the dimensions of the arms, the breadth and thickness of the oval being indicated as follows: "6|" X 21""; this is a "short cut" which will usually answer, but it does not actually show the section of the arm. It would be better actually to make a cross section, as shown in the lower portion of the right-hand view, giving the actual radii for the section, as otherwise the pattern maker might make an arm more or less blunt on the ends than the draftsman intended. Spur Gear. Fig. 40 shows the detail of a spur gear with a T= shape arm. The gear drives through fitted bolts in the flange about the hub. Two or three teeth are dotted in, to show their dimensions, which are according to the standard involute system. Pinion for Spur Gear. Fig. 41 shows the detail of a pinion designed to mesh with the gear in Fig. 40, one view being sufficient. Pair of Beveled Gears. Fig. 42 shows the detail drawing of a pair of bevel gears. By careful study of this drawing, the student will gain an idea of the dimensions to be shown on a bevel gear. The gear-cutting machines, on which the teeth of these gears are cut, require the angles as given for the setting of the cutters. It should also be remembered that the casting must be finished by the machinist before the teeth are cut; hence the dimensions for hubs, diameters, etc., must be so put on that they can be conveni- ently used by the machinist in turning up the gear blank in an ordinary lathe. Worm and Worm Gear. Fig. 43 shows the detail of a worm and worm gear. The teeth on the worm gear are twisted; and if it were attempted to show their true projection, it would be a compli- cated and difficult piece of work'. The worm gear is shown, there- fore, by drawing the pitch line of the teeth and other circles at the PINION CUT-13 TrZD.R-mVOLVTE ONE-STEEL -F.A.O. Fig. 41. Detail of Pinion to Mesh with Gear of Fig. 40 50 MACHINE DRAWING a o '3 s a o pq 52 MACHINE DRAWING top and bottom of the teeth. At the point where the gear is in mesh with the worm, a portion of the rim is broken away, and the middle section shown. The worm threads, which are lines in the form of helices, are shown in the drawing merely by straight lines, this being the conventional way for representations of this character. Another way of showing the worm would be in cross section, in which case the helical lines would be wholly avoided; as drawn, however, it has the advantage of at once conveying to the eye that it is a right-handed thread. CYLINDER HEAD ONE- C.J. Fig. 44. Detail of Cylinder Head of Steam Engine Cylinder Head. Fig. 44 shows the cylinder head of a steam engine. Although in the drawing the entire circle is shown, it would have been just as clear if only one-half had been shown, similar to the manner of showing the side views of the gears just discussed. In the plan view, it should be noted that the tapped holes are indicated by double circles, while the drilled holes show a single circle. The inner circle for the tapped holes is intended to represent the bottom of the thread, while the outer circle represents the top of the thread. Another conventional method for a tapped hole is to fill in the circle entirely with black ink; the method illustrated, however, is the most common. MACHINE DRAWING 53 Water Cylinder for Triplex Pump. Fig. 45 shows a water cylinder for a triplex pump, and is an excellent illustration of many of the points heretofore brought out, combined on a single drawing. This drawing should be carefully studied in detail. Note the general boldness of the lines, and the sharp contrast between the full-line work and the center, dimension, and dotted lines. Note that in the J^iwmS^t ■*£— i 4^^\ Fig. 45. Detail of Water Cylinder for Triplex Pump cross-sectional views the dotted lines have been almost entirely eliminated, thereby leaving the section work clear and plain. There is no necessity of showing parts in dotted lines which are beyond the plane of the section, but in several places just enough simple dotted work is shown to convey the relation of the parts. Object of Each View. Each sectional view is made for a spe- cific purpose, and that purpose is never allowed to be obscured. The top plan is mainly to show the upper portion of the water cyl- 54 MACHINE DRAWING inder; the cross section below it gives the principal interior view; the right-hand half-elevation and cross section are for the purpose of showing the face of the valve chamber and the interior of the valve chamber; the horizontal cross section in the upper right-hand corner of the drawing shows not only the interior of the barrel and valve chamber at two different points, but also a clear outline of the base of the entire casting. Each view must be used with the other to get a clear idea of the construction; but each view is so simple in itself that no confusion arises in the mind as to what its lines mean; one view is readily associated with the other, and the grouping of the four views is such that the eye passes easily over all of them. Method of Grouping Dimensions. Note the grouping of the dimensions, following in general the purposes of each of the views as explained above. On the top plan are given the dimensions affecting the top of the casting only. On the principal vertical cross section are given the greater part of the dimensions for the entire piece. This is as it should be, for the dimensions should always be grouped as much as possible on the principal view of an object, provided they can be clearly put on that view and not become so numerous as to cause confusion. A drawing over which the eye has to wander widely in search of the several dimensions of the same portion, is slow and difficult to read. On the right-hand half-elevation and cross section are the figures for the outline of the face of the valve chamber, and the location of the tapped holes for the hand-hole cover-bolts. On the horizontal cross section are given the figures for the interior dimensions of the valve chamber, and a complete dimen- sioning of the base of the casting. The special attention of the student is called to this systematic grouping of the dimensions on the view which will most clearly show them. A glance at this draw- ing is sufficient to suggest what a confusion of figures there would have been, had it been attempted to place them all on two views, and if, instead of cross sections, full and dotted lines had been used. Method of Showing Finished Surfaces. On this drawing is indicated a new method of showing finished surfaces. Each surface which is intended to be finished in the machine shop, has drawn next to it a medium-weight line consisting of a long dash and two dots. This method of showing finished surfaces is not as common as the MACHINE DRAWING 55 one heretofore used, of writing the letter / across the line; it has the advantage, however, of conveying an absolutely definite idea of the extent of the surface to be finished, and in some instances is especially valuable on this account. It is a good way of specifying the finish ; but for general practice the letter / is simpler and perhaps more readily and universally understood. Analysis of Drawing. This drawing, while not complicated, contains quite a large number of dimensions, and is a good example of the principle of systematic figuring. The student's attention, therefore, is called to the following analysis of the dimensions on the drawing. The casting consists of a barrel, in which the plunger slides, with a stuffing box at the top and a waterway at the bottom leading into the valve chamber; attached to this barrel is the valve chamber, consisting of two compartments, the lower one for suction, the upper one for discharge; to support both barrel and valve chamber and permit of their being bolted to the water-supply casting, a rectangu- lar base is provided. Beginning at the top of the casting, the figures for the stuffing box, inside and outside dimensions and thicknesses are given, and note made that the outline is square. The tapped holes for the gland studs, and bosses for the drips, are shown most clearly in the top plan, and are therefore dimensioned there. Next we come to the bore of the barrel to receive the plunger, and here the square shape of the casting changes to a round, the diameter and thickness of metal being given. Below this cylindrical part is the waterway, the height of which (2\") is given, and then the V thickness of the base below. This completes practically all the dimensions of the barrel and stuffing box. Passing to the valve chamber, it is first necessary to locate the center line of same in reference to the barrel (10f" centers). This being done, the arrangement of valves is dimensioned, and figures given for the valve chambers, thus — length, breadth, depth, thick- ness of metal, fillets, etc. ; then follow the location of the face of the valve chamber, 5| Y from the center line, and the layout for the hand- hole cover; then the location of the upper face of the valve chamber, 14J" from the base, and the layout for the flange of the discharge pipe, which is shown on the top plan. 56 MACHINE DRAWING Few figures as yet have been placed on the base of the water cylinder; these are now completed by starting at one side of the base and going completely around same, giving not only external dimen- sions and radii, but also location of bolt-holes and their sizes — all of which are shown in the horizontal section. This completes the dimensions; and if the student has carefully adhered to each particular part of the casting until completely dimensioned, and has not passed in haphazard fashion from one portion of the casting to another, he will have succeeded in dimen- sioning the piece with absolute completeness. No part will have escaped being dimensioned, and no part will be dimensioned twice. It would be a good plan for the student to copy this drawing, using a scale of 3 inches to the foot, and, in making the drawing, to follow the description as given above in reading the figures from the cut. He will thus more clearly realize the systematic progress from one part of the casting to the other, and will himself check the figures shown. Hoisting Drum. Fig. 46 shows the detail of a hoisting drum to carry wire rope. Attention is called in this detail to the enlarged cross section of the rim, conveniently placed to show clearly the style of the groove. It should also be noted, that, instead of drawing the grooves the entire length of the drum, but a few are drawn at each end of the drum and a note placed against same to indicate that the grooves are to be cut the entire length. This is another " short cut" consistent with the definition of a working drawing. The breaking away of a portion of a view is illustrated in the right-hand elevation, in which a small section is exposed to show the method of fastening the end of the wire rope. Crane Drum Grooved for Chain. Fig. 47 shows a crane drum, grooved for chain, and carrying its driving gear and shaft. This is a very good illustration of the economy of grouping parts together, instead of detailing them separately. It is obvious that the drawing of each detail is just as clear as though it were separately drawn. In fact, the information conveyed is the most complete possible; for not only are the figures for each part clearly shown, but the exact manner in which the parts go together, thus enabling the workman to understand at a glance the assembling of the parts, and to make Iiis fits accordingly. A general drawing for this purpose alone has MACHINE DRAWING 57 MACHINE DRAWING 59 to be made in the case of a complicated machine; and it would be confusing to put on such a drawing figures sufficient to detail each part. The draftsman who can properly judge when to use assem- bled drawings for detail dimensions, and when to avoid such use, will save a large amount of time and money in the production of drawings for shop use. A common rule that "every part shall be detailed separately" is in vogue in many drafting rooms; but it is seldom followed literally, and when so followed becomes a drag on office efficiency. A better rule is — "Detail every part separately when groups of parts cannot be clearly detailed together." Note on this drawing the method of indicating, by light diagonal lines across the shaft, the location of the bearings; also the enlarged view of a few teeth of the gears, with sufficient figures for the pattern maker to work out the teeth. These gears are "half-shrouded", or strengthened by a rim extending up to the pitch line. BEARING SHAFT ONE -STEEL- F.A.O . Fig. 48. Detail of an Ordinary Shaft Detail of Ordinary Shaft. Fig. 48 shows the detail of an ordi- nary shaft with a number of different bearings and fits upon it. It illustrates most of the common points which are necessary to be specified on shaft details. The distance, shoulder to shoulder, is usually given throughout the entire length of the shaft, and these distances summed up for the "over-all" dimension. The "over-all" dimension is important, because from it the stock is ordered and cut off; and the workman should not be required to add up a lot of figures to secure it. Fillets should be allowed at every shoulder, if possible, and their radius specified; in this way there is less liability to the formation of incipient cracks than if the corners are left sharp. Keyways should be carefully dimensioned and located. Bearings should be indicated by light lines running across the shaft diagon- 60 MACHINE DRAWING ally; and it is good practice to print the name of each piece to which the shaft is fitted, just above the shaft at the point where such fit occurs, or the parts themselves are partially shown in light lines, as at A and B in the figure, thus enabling the workman to make the fits more intelligently. It is common practice to make all holes which receive shafts of exactly "gauge diameter", and to make the allowance for the fit in the shaft. For example, a "3" running fit" would mean that the hole in the piece to receive the shaft would be exactly 3" in diameter, while the shaft would be, say, "3" less .003"". Sometimes this allowance is indicated by giving the actual number of thousandths of an inch under size, as noted ; sometimes by calling for a "running fit", or a "wringing fit", or a "pressed fit", or a "drive fit", or a "tight fit", as desired. "Broken" Pieces and "Out=of=Scale" Dimensions. Shafts are often so long that it is difficult to represent their entire length on the sheet to the scale chosen. They are then "broken", as shown in the figure, and crowded up to a shorter length, the dimensions being depended upon to give the proper relation of the parts. When there is occasion, because of some change, to alter a dimension on a finished drawing, it is usually permissable to change the dimensions without rubbing out the lines of the drawing, pro- vided that no considerable number of other dimensions are affected, and provided that some sign or note is made on the drawing, calling attention to the fact that the dimension has been changed and that the drawing is "out of scale". Sometimes the dimension is placed in a circle thus @ or a line drawn beneath it thus, .£" ; or the words "out of scale" placed after it thus, s " (out of scale). Although workmen are not allowed to "scale" drawings, yet it is dangerous to have dimensions which are out of scale on the drawings unless special attention is called to that fact. The above remarks on "broken" pieces and "out-of-scale" dimensions are equally applicable to all details as to shafts, the points merely being illustrated by the figure under discussion. Bearing Stand with Cap and Boxes Removed. Fig. 49 shows a bearing stand with the cap and boxes removed. There is little of special note to discuss in regard to this, beyond calling attention to the general nature and type of the piece illustrated. The design is characteristic of pedestals and bearings found about stationary MACHINE DRAWING 61 engines of large size. Such parts are usually massive and heavy in their proportions, with well-rounded corners and smooth outline. The closed-box form of casting affords maximum strength with good distribution of material, and at the same time conveys to the eye the effect of a solid piece throughout. ^/J DRILL Zg" LEVELING SCREWS I § DRILL BEARING STAND ONE -C. J. Fig. 49. Detail of Bearing Stand with Cap and Boxes Removed Sample Letters. Fig. 50 shows a sample sheet of plain letters, such as are particularly applicable to working drawings. They are especially devised for easy, quick, and uniform strokes. Each draftsman has a character of his own in lettering and figuring, and the form of lettering which is most natural for him to use is the one 62 MACHINE DRAWING he will use to best advantage. It is necessary, however, to confine draftsmen to a general type in order to make their work reasonably uniform; and the sample sheet (Fig. 50) represents not only the most common type in use, but a type to which almost any draftsman can readily train his eye and hand. Whether the slopes are forward Small Letters ,2 i i I I 2 1 23 n/:fhhf:.dt.i&£" , ff s nt':j hh /^ jj , kH , A mrr\ nrS 12 I 2 12 12 ,t„ 12 12 123 4 12 I 2 123 :oti, pp. rjrf r t" , x , lt e , uit , -v\/ , w \w , x y\ tji i ? abcdefahijklmnopqrstuvwxYZ. CAPITAL LETTERS. A/Auih t\ ni'y FthA utv- , w j jj'kIK , i, m, A/ (){> P#. ty K/'A A', t iH)VWXY7£— ABCDEFGHIJKLMNOPQRSTUVWXYZ&. MA^h/fiftH AiMiiii 1234567390. ABGDEFGHIJK-LMNOPQRSTUVVSIXYZ &. Fig. 50. Sample Sheet of Plain Letters Used in Working Drawings or backward, or straight up and down, is of little importance, as long as the general style is maintained. Drawing Room Practice. Every drafting room has certain methods and rules peculiar to its own organization and that of the shop to which it supplies drawings. While it is impossible to formu- late any set of instructions which will cover all situations, the accom- panying sheet, "Drawing Room Practice," is consistent with general practice in modern drawing offices and the fundamental principles discussed elsewhere in this book. It is a condensed code of pro- cedure which the student will do well to hang in some convenient location near his table, and to consult freely as he works. It should not take the place of the explicit discussions of the text, but should be used as an index to it and as a reminder. MACHINE DRAWING 63 CHICA G O DRAWING ROOM PRACTICE AMERICAN SCHOOL OF CORRESPONDENCE ILLINOIS STDSJZES PLATES DRAWNGS MARGINS SCALES TRIMMING SIZE 9"* 12" (Z"x/8" 18" * 24" 24"* J 6" PROJECTION DOTTED LINES PENCIL WORK TR. CLOTH [CHARACTER OF LINES COLOR FIGURES VIMENSIOm ALLOWABLL ERROR NOTES THOUGHT I TITLE FRAME l"x2" /"x2" 22X4" 2?*4' ALLMARG/NS fwiDE USE THESE SCALES IN PREFERENCE TO OTHERS 12"= F FULL SIZE 6"=/' HALF » 3"= F QUARTER » //=/' EIGHTH » CYLINDER FOR 12x36 CORLISS ENGINE AMERICAN SCHOOL of CORRESPONDENCE CHICAGO ILLINOIS SCALE 3 = r JULY 7J9/3. C.X.&. {SAMPLE TITLE) CHOOSE LARGEST SCALE CONSISTENT WITH SIZE OF SHEET- USE SIMPLE PROJECTIONS ONLY. MARE VIEWS TO COMPLETELY ILLUSTRATE. NO MORE- NO LESS! PLACE VIEWS ON SHEET IN SAME POSITION AS PIECE OCCUPIES- IN ASSEMBLED MACHINE. WORK ALL VIEWS TOGETHER. DO NOT TRY TO FINISH ONE VIEW BEFORE BEGINNING ANOTHER. USE FEW DOTTED LINES ONLY WHEN ABSOLUTELY NECESSARY. USE CROSS SECTIONS FREELY IN PREFERENCE TO DOTTED LINES. MAKE PENCIL DRAWING SHARP AND DEFINITE, ABSOLUTELY COMPLETE, AND CHECK CAREFULLY BEFORE TRACING. USE ROUGH SIDE OF TRACING CLOTH TO PREVENT CURLING. LINES FOR SIMPLE LARGE SCALE DETAILS THUS: ■ » COMPLICATED SMALL » >' *- » DOTTED » » CENTER OR AXIAL {$%H} AND D0T „ » DIMENSION v i v//////// " 1- » CROSS SECTION £ TO § APART |p§§f USE BLACK INK FOR ALL LINES MAKE FIGURES BROAD, BOLD AND ABSOLUTELY CLEAR. MAKE ALL FIGS. READ FROM LOWER OR RIGHT HAND SIDE OF SHEET- MAKE ALL DIMENSIONS IN INCHES UP TO AND INCLUDING 36 INCHES. ANY DIMENSIONS NEED OCCUR BUT ONCE ON SAME DRAWING. DIMENSIONS OF PARTS OF A MACHINE REQUIRING GREAT ACCURACY SHOULD BE INDICATED ON DRAWING WITH PLUS AND MINUS ERROR THUS: DIAMETER OF SHAFT 3.625" ±%%%'> USE ENOUGH DIMENSIONS TO ENABLE THE PIECE TO BE MADE NO MORE-NO LESS! USE NOTES FREELY TO CLEAR UP DOUBTFUL POINTS. ALWAYS HAVE IN MIND THE WORKMEN WHO ARE TO USE THE DRAW1NG S THE PATTERN MAKER. BLACKSMITH AND MACHINIST. ALWAYS CONSIDER THE MACHINES AVAILABLE FOR THE WORK. ~4f- 64 MACHINE DRAWING PLATES Plates I to IV inclusive are to be made by the student as an examination on the work of Machine Drawing, Part I. These plates are to be the same size as those of the preceding Instruction Papers of the course, viz, 11 inches by 15 inches outside, with a margin of \ inch, making the clear space for the drawing 10 inches by 14 inches. PLATE I Sketches. From Plates II and III make rough, freehand sketches of the parts, paying no attention to scale or arrange- ment on the sheet. Simply make them of such size as to get them all on the standard sheet as specified. Use a medium pencil, and try to make the sketches quickly. Put on all the dimensions. Do not try to get smooth, straight lines, but dash off boldly with the pencil, aiming merely to get clearness and definiteness. Make the sketches over two or three times, noting any improvement in rapidity or effectiveness, and submit the best one. PLATE II Water Plunger. This represents the plunger for a water cylin- der of an ordinary pump. Make the drawing to a scale of 6 inches to the foot, and instead of copying the plate, use the sketch made on Plate I. This will not only give practice in working from a rough sketch, but will show whether all the information is on the sketch. PLATE III Valve Motion Details. This represents some of the details of the valve motion of an ordinary pump. Make the drawing to a scale of 12 inches to the foot, or full size, and as before, instead of copying the plate, use the sketches made on Plate I. Note that this plate requires the shade lines to be put on. This being a full size drawing, will stand very bold heavy lines, thus insuring a good blue print. This plate is to be made on tracing cloth, laid over the pencil work. PLATE IV Water Valve Details. This represents the complete valve mechanism for the water cylinder of an ordinary pump. Make the drawing to a scale of 12 inches to the foot, or full size. Although it MACHINE DRAWING 65 is evident from the plate that this is a case where the dimensions can be placed on the assembly drawing without confusion, yet in order to give practice in detailing from an assembly drawing, the student is required to detail each part separately in the space to the right of the assembled valve as shown. The assembly view should first be made, copying the plate. Then, instead of placing the dimensions on the assembly view as shown, they should be placed on each indi- vidual detail as drawn. There are five parts to be shown, and the arrangement of these on the sheet, and the number of views necessary for each are left entirely to the student. This is a good opportunity to produce a nice, well-filled sheet, workmanlike in execution and arrangement, by exercising careful attention to the principles laid down in the foregoing pages. This plate should be made on tracing cloth laid over the pencil work. p w H O s w 3 or PITCH A = £ or d Fig. 71. Enlarged U. S. Standard Thread IS the angle between the two sides of the thread is 60°, so that if the thread came to a point at the top and bottom, as indicated by the dotted lines, the depth of the thread D would be about T Vo of the pitch P. The sharp corners, however, are a disadvantage, since on the outside they are likely to be bruised and to give trouble in putting on the nut, and at the bottom of the groove they tend to weaken the bolt or screw. In order to avoid these sharp corners, the threads are flattened in the United States standard thread, as shown in Fig. 71, the amount of this flattening being such that the distance C is J of the pitch, or — what amounts to the same thing — the distance A of D. This gives a thread whose depth E is j%% of the pitch. Whitworth Standard Thread. Fig. 68 illustrates what is known as the Whitworth standard thread, shown enlarged in Fig. 72. Here the angle between the sides of the thread is 55°, so that if the threads came to sharp corners, as shown by the dotted lines, the depth D would be tVo of the pitch. The top and bottom of the thread, instead of being flattened, are rounded off so that the distance A is | of D, or the depth E is tVo of the pitch. Lag Screw V Thread. Fig. 69 shows the V thread as used on lag screws and other wood screws. Here the groove is much larger than the thread, because the wood into which it is to screw is weaker than the iron of which the screw is made. Variation of Square Thread. Fig. 70 shows a slightly modified form of square thread, the only difference between this and the square thread previously described being that the sides of the groove taper slightly. Conventional Representations of Screw Threads. The student should the drawing of the threads, as previously ex- plained; and every draftsman should be able to draw the true pro- jection of a thread if he should have occasion to do so. It is evident A = / OF D Understand Fi S- 72 ^ Enlarged Whitworth Standard Thread MACHINE DRAWING 81 however, that the process is complicated, and on a screw of small diameter and pitch it would be difficult to follow out the construc- tion. To avoid this labor the construction shown in Figs. 73, 74, and 75 may be adopted, straight lines being substituted for the projections of the helix. Fig. 73 shows the conventional representa- tion of the plain, single, right-hand V thread, the true projection of which was shown in Fig. 62. To make the conventional drawing (Fig. 73), draw the parallel lines AB and CD at a distance apart equal to the outside diameter of the screw, and draw the line AC perpendicular to these two lines. Along A, lay off the distances AE, EF, etc., each equal to the pitch. Along CD, lay off C H equal to \ the pitch; and from H, lay off HI, IJ, etc., equal to the pitch. Draw lines from A to H , E to I, etc. Now, if the depth of the thread AS is known, draw the lines ST and UV; and begin- ning at L, perpendicularly under a point halfway between A and E, lay off LM, MN, etc., equal to the pitch. In like manner find the points 0, P, R, etc., and draw the lines LO, MP, etc.; also AL, LE, HV, HO, etc. The dotted lines should be left out in the finished drawing, but are put in the figure to show the construction. If. instead of knowing the depth AS, we know the angle between AL and LE, the depth can be found by drawing from A and E the two lines AL and EL in such a way that they make the required angle with each other. To do this, the lines AL and EL should each make an angle with the line AB equal to 90° minus J the angle between AL and LE. Fig. 74 shows the corresponding construction for the United States standard thread. Draw the lines AB, CD, and AC as in Fig. 73, and find the points E, F, G, H, I, J, K, etc., in the same way as in that case. Now draw the lines S T and UV so that AS and CU shall equal tW of the pitch AE. On the line AB, lay off from H Fig. 73 Conventional Drawing for Right- Hand V Thread 82 MACHINE DRAWING Fig. 74. Conventional Drawing for U. S. Standard Thread A a distance Al equal to T V of the pitch; and on each side of E, F, G, H, etc., lay off E2, E3, etc., each equal to i\ of the pitch. From the points thus found, draw lines 1 — 4> ® — 5, etc., making an angle of 60° with AB. The rest of the drawing is completed as shown by drawing in full lines those parts of the lines AB, CD, ST, and UV intercepted be- tween 1 — 4 and 2 — 5, etc. Fig. 75 shows the conven- tional representation of a square thread, and is drawn in exactly the same way as the true pro- jection shown in Fig. 65, except that straight lines are used instead of curves, and certain other minor lines omitted. Square threads are seldom conventionalized more than as shown in Fig. 75, and V threads of coarse pitch and large diameter are usually drawn as in Fig. 73, whether sharp or U. S. standard. But for ordinary screws of small diameter and fine pitch, as are most frequently used, such a method involves too much labor, and the use of alternate long and short dashes across the body of the screw, as shown in Machine Drawing, Part I, Fig. 14, is universally employed. CAMS Mechanical Action. A cam is an ap- plied form of the ordinary wedge. The simple wedge is used to split apart the piece into which it enters, or to pry up heavy weights. It does not automatically repeat its work. The work of the wedge is fin- ished when it is once driven home; and its function is not to produce motion, but to give mechanical advantage to the blows which drive it. If we take a simple wedge and fasten it to some piece — say, a disk centered on a shaft, which is capable of continuous or periodic Fig. 75. Conventional Draw- ing for Square Thread MACHINE DRAWING 83 FOLLOWER WEDGE rotation, and allow the face of the wedge to rub against another guided piece, called the follower, we have a cam. In Fig. 76 is shown a double wedge in which either sloping side produces against the follower the action just referred to. When we rotate the cam, it "wedges" the follower along a fixed path. When the fol- lower reaches the top of the wedge, it may drop back to its original position, drawn by gravity or by the force of a spring, or it may be eased back by another wedge in the reverse position of the other, as shown in Fig. 76. This cycle will be repeated as long as we choose to rotate the cam. The cam, therefore, is essentially a repeating wedge, and its function is primarily one of motion rather than of great force. The wedge principle, however, enables very powerful cams to be made in cases where but little motion is desired. The motion of the cam is usually a rotation, but it may be an oscillation, or a straight-line reciprocating motion. Factors in Design and Layout. In designing a cam, it is not only essential that the proper layout be made to pro- duce, theoretically, the required motion of the follower, but that the wedge action be such that the cam will drive easily. Re- ferring again to the wedge as a machine, a thin wedge, for example, may be forced under a heavy weight with a sharp blow, whereas a thick broad wedge cannot be made to lift the weight. For precisely the same reasons, cams designed with thin wedges will drive their followers with ease, while cams may be designed so steep in their wedge action that they drive with difficulty, and may even lock the follower in its path, on account of excessive side pressure. This is a very important ele- ment in a design, and the analysis will be brought out more clearly in the discussions of the line of pressure. The actual laying out of a cam is simple in principle, although somewhat tedious, especially in complicated cams. Several posi- tions of the follower in its path are chosen, the follower drawn in those positions, and then the face of the cam is drawn tangent Fig. 7G. Simple Diagram of a Cam 84 MACHINE DRAWING thereto. In order to do this, the several positions of the follower in its path may be laid down on the drawing paper as shown in Fig. 77. This fixes the limit through which the cam must move the follower. Now develop the cam itself on a separate piece of transparent paper or tracing cloth, Fig. 78, and place this over the follower layout with the centers of the two draw- ings coinciding, and a pin through this center of rotation of the cam. As the cam is rotated about this axis so as to correspond to the various positions of the follower shown on the drawing underneath, the follower can be traced in on the "follower upper-drawing in each position. When the movement of the cam is complete, we have on the cloth a series of drawings of the follower; and, if we draw a tangent line to these, the line of the cam will be produced. This method, however, from the drawing-board standpoint, is clumsy and inaccurate, because of the wearing of the pinhole and the error of trans- ferring the shape of the follower to the tracing cloth. It is readily seen by reference to Figs. 77 and 78, that the same result will be attained in a much easier and more accurate manner if we artificially rotate the follower about the cam on the drawing-board by means of a pair of compasses, laying off equal angles to complete one revo- lution of the cam and show- ing the follower in position at each step. This is shown in Fig. 81, and is the method usu- ally followed in cam design. This does not mean that the tracing-cloth method should be discarded, for it is useful in studying complicated cam move- ments; and also in testing the cam development when it is completed, to make sure that no error has been made. CENTER OF CAM Fig. 77. Layout for Posi tions of Cam Follower Fig. 78. Layout for Cam MACHINE DRAWING 85 PRACTICAL EXAMPLES IN LAYING OUT CAMS Statement of Problems. From the principles just stated, the uniform course of procedure in laying out a cam is as follows: 1. Draw the follower in several positions in its path. 2. Draw cam radii corresponding to these positions. 3. Rotate the follower about the cam. 4. Draw tangent line. 5. Test the cam. 6. Draw the line of pressure for each position. Plate Cams with Uniform Motion In Figs. 79 to 86 inclusive, it is required to move the follower F with uniform motion from position to 6, w T hile the cam rotates through 150°; it is then to remain at rest during a cam movement of 30°; then to return to its original position, moving uniformly from position 6 to 0, while the cam turns through the remainder of the circle, or 180°. This is briefly expressed as follows: Uniform rise 150°; rest, 30°; uniform fall, 180°. Example 1. Pointed Follower with Path Intersecting Cam Center. 1. Folloiver Positions. The length of travel 06, Fig. 79, is supposed to be known, being fixed by some requirement of the machine to which the cam is to be applied. This distance, for a uniform motion, should be divided into any convenient number of equal parts; the more divisions, the more accurately can the cam be drawn. In this case six spaces are chosen. 2. Cam Radii. The diameter of base circle D is arbitrary; and its center having been chosen, draw the original radius CO; then the radii CX and CB, limiting the arcs of rise, rest, and fall,, res- pectively, should be drawn. As the follower must rise J of its travel while the cam rotates J of its arc, there must be as many equal divisions of the cam arc as there are of the follower travel. Hence the arc of rise OX is divided into six equal parts and the radii are drawn. Similarly, the arc of fall OB is divided into six equal parts and the radii produced. 3. Follower Rotation. The rotation of the follower about the cam is accomplished by setting the point of the compasses at C, and, with radius Cl , striking an arc intercepting the radius corresponding to position of the follower at R v Similarly, points R 2 , R 3 , R v R & , 86 MACHINE DRAWING and jRg are found. As the follower rests from X to B, the arc of intersection for R a is continued to F R . For the period of fall, arcs 6' are swung from the same points of follower travel as before, making the intersections F 5 , F v F 3 , F 2 , F v 4. Tangent Line. A smooth curve is now drawn through the points of intersection, thus forming the outline of the cam. For other forms of follower than a sharp point, this line would be strictly Fig. 79. Diagram for Cam with Pointed Follower Whose Path Intersects Cam Center a tangent line to the face of the follower. A pointed follower, as shown in the figure, is not a very practical form, as the point is subjected to severe wear. It is chosen for the present illustration, to afford the simplest possible cam development. 5. Testing. The cam may be tested by laying over it a piece of tracing cloth, and tracing roughly the outline of the cam, also marking the radii and the center of rotation. A pin is now placed at the center of rotation of the cam, and the tracing cloth swung MACHINE DRAWING 87 until the several radii CR V CR 2 , CR 3 , etc., fall into the line of travel CT. If the cam is correctly developed, it will just touch the several positions of the follower in its path when the proper radius is coin- cident with the line of travel C T. It is very easy to make a mistake in laying out cams, especially the more complicated ones; and this rough method of proving the work should always be applied. 6. Pressure Line. The face of the follower in this case is a point, and the pressure line, being the common normal between the cam and follower at point of contact, is always theoretically normal to the cam at that point. During motion, however, the force of friction between the cam and follower would modify somewhat the direction of the pressure line, turning it so as to produce a side thrust against the follower, causing consequent chattering and possible binding in its guides. This can be minimized by ample lubrication and hardened faces; but for cams which have any considerable load to work against, a follower carrying a roll against the cam is a necessity. The line work in cam design should be fine and accurate. A hard pencil, kept well sharpened, is necessary, and special care must be taken to get definite intersections. In order to keep the center of the cam in as good condition as possible, it is well not to continue the radii to the center, but to stop when a short distance from the center, as shown. When penciling and inking in, use a fine, continuous line, not dotted; the continuous line is more quickly made and is apt to be more accurate than the dotted line. More- over, the cam is strictly layout work, not finished in detail, and the subsequent detail drawing of the cam should not be confused with the layout of the cam outline. Example 2. Pointed Follower with Path Not Intersecting Cam Center. 1. Follower Positions. The follower positions, Fig. 80, are chosen and drawn precisely as in Fig. 79; in this case, however, the path of the follower does not intersect the center of the cam, but, if produced, would pass at some distance to one side of it. This changes materially the development of the cam, as will subsequently be noted. 2. Cam Radii. The diameter of base circle and center of cam being chosen as before, draw the original radius CO. This original radius is the one to which all subsequent radii are related. Treating 88 MACHINE DRAWING this radius the same as the original radius CO in Fig. 79, the radius CX is drawn, making the arc of rise 150° as before. The radius CB is then drawn, giving the 30° arc of rest, and leaving the arc of fall between CB and CO 180° as before. Since the cam is to have uniform motion, the subdivisions of the arcs are equal, and are made in exactly the same manner as in Fig. 79. 3. Follower Rotation. The follower is now rotated about the cam by the compasses, in similar manner to that in Fig. 79, pro- Fig. 80. Diagram of Cam with Pointed Follower Off Center ducing the intersections R v R 2 , R 3 , R v etc. Now, however, the introduction of a new step should be noted. The original radius CO, not being coincident with the path of the follower OT, the inter- sections jRj, R 2 , R 3 , etc., do not represent the actual positions of the point of the follower when rotated. During the arc of rise, the follower is gaining on the radius, and the increasing distances R 1 L V R L*, jR 3 X 3 , etc., must be set off ahead of the radii, equal to the L 2^2> distances Hi, K2, J3, etc. In similar fashion, during the arc of MACHINE DRAWING 89 fall, the decreasing distances F G N Q , F 5 N 5 , F A N v F 3 N 3 , must be set off ahead of the radii, equal to Q6, P5, M4, J3, etc. 4. Tangent Line. A smooth curve is now drawn, not through the original points of intersection with the cam radii, as in Fig. 79, but through the points set off as above from these intersections. In other words, the cam curve is drawn through points L v L 2 , L 3 , L 4 , etc., and iV 6 , N s , N 4 , N 3 , etc. 5. Testing. A piece of tracing cloth should be laid over the cam, the outline traced upon it, the radii marked, and then the tracing cloth rotated about the pin point, as in Fig. 79, to see if the cam in its suc- cessive positions just touches the follower in each of its positions. 6. Pressure Line. The pressure line at each position of the follower is, as in Fig. 79, normal at the point of contact. Example 3. Roll Follower with Path Intersecting Cam Center. 1. Follower Positions. In Fig. 81, the case is identical with that of Fig. 79, except that the shape of the follower has been changed to the more practical form of a roll, which can turn about a pin, thus relieving the crowding, grinding action characteristic of the pointed follower hitherto discussed. The path of follower roll F is divided as before into six equal parts. 2. Cam Radii. The original radius CO, the radius CX, limiting the arc of rise, the radius CB, limiting the arcs of rest and fall, are all drawn precisely as before, and the subdivisions of the arcs are in nowise changed from the preceding cases. 3. Follower Rotation. The follower is now rotated about the cam, giving the intersections R lf R 2 , R 3 , R v R 5 , and jR 6 for the period of rise; the corresponding intersections for the period of fall are F 6 , F 5 , F v F 3 , F 2 , and F v With each of these intersections as a center, and a radius equal to the radius of the follower roll, an arc is struck, which represents the follower in its rotated position. 4. Tangent Line. A common tangent line is now drawn to the several positions of the rotated follower, giving the outline of the cam as a smooth curve. In order to give the follower its full period of rest from i? 6 to F 6 , the portion of the cam lying between the radii CX and CB must be a true arc of a circle struck from center C. Special attention must be paid to this point, because, if the true arc is not maintained between these radii, the full period of rest will not be secured. 90 MACHINE DRAWING 5. Testing. The testing of the cam is accomplished in the same way as previously described, by the tracing-cloth method. The several positions of the follower in its path should be drawn; and as the cam is rotated into its several positions, if the work has been accurately done, the cam will be perfectly tangent to each position of the follower. 6. Pressure Line. By a well-known principle of mechanics, when two bodies are in contact, the line of pressure between them is Fig. 81. Diagram of Cam with Roll Follower on Center Line always perpendicular to the surfaces at their point of contact; in other words, the line of pressure is the common normal at the point of contact. The follower being a true circle, the perpendicular at any point of its surface must pass through the center of the roll; therefore, if we draw a line from the center of each position of the roll to the point of contact between it and the cam, this line will MACHINE DRAWING 91 be the line of pressure between the cam and the roll. This has been done in Fig. 81, and the arrows indicate the direction of the pressure of the cam against the roll. In order to group these lines of pres- sure so that the action may be clear as the follower moves over its path, the lines of pressure as drawn are rotated back to the corres- ponding points in the path of the follower. By this it is readily seen that during the period of rise the lines of pressure are all slightly inclined towards the left of the line of travel, while during the period of fall the lines of pressure are all slightly inclined towards the right. The cam as shown in Fig. 81 is a very good cam, so far as the lines of pressure are concerned. The ideal condition would be to have the lines of pressure all coincident with the line of travel. This is impos- sible, because the only shapes which would give a common normal along the line of travel would be two circles, revolving about their centers, and such a cam could give no travel to the follower. The fact that the lines of pressure are at such a slight angle to the line of travel indicates that there is very little side pressure on the follower and that, therefore, the cam will be an easy working cam. Example 4. Roll Follower with Path Not Intersecting Cam Center. 1. Follower Positions. The follower positions in Fig. 82 are chosen precisely as in Fig. 81, and the subdivisions of the path of the follower similarly made. This case corresponds with that of Fig. 80, the line of travel not intersecting the center of the cam. The shape of the follower, however, is a roll similar to that just discussed in Fig. 81. 2. Cam Radii. The original radius CO is drawn as before. Then the radius CX, limiting the arc of rise, the radius CB, limiting the arcs of rest and fall, and the subdivisions of the arcs of rise and fall, are made exactly as in Fig. 81. 3. Folloiver Rotation. The treatment of follower rotation is the same as that in Fig. 80. The intersections R v R 2 , R 3 , etc., being found, the distances R. 1 L V R 2 L 2 , R 3 L 3 , which the follower gets ahead of the radii, are set off exactly as in Fig. 80. In this case, however, the points L v L 2 , and L 3 are the centers of the rotated follower roll; and from these centers are struck the arcs representing the follower roll in its several rotated positions. 4. Tangent Line. A smooth tangent line is now drawn to the several positions of the rotated follower, thus giving the outline of 92 MACHINE DRAWING the cam. In this case the outline of the cam giving the period of rest lies between the radii CN 6 and CL 6 . In order that the full period of rest may be accomplished, it is necessary that the portion of the cam between these two radii be a true arc, struck from center C. Special attention should be given this point. 5. Testing. The cam should be tested by the tracing-cloth method, as before. 6. Pressure Line. The pressure lines are drawn as in Fig. 81 Fig. 82. Diagram of Cam with Roll Follower off Center by joining the center of the follower roll in its rotated positions to the point of contact between the cam and the roll. Arrows, as before, indicate the direction of the pressure. These pressure lines may be rotated until they are collected along the line of travel, indicating the change in direction of the pressure between the cam and the roll as the roll passes over its path. A convenient MACHINE DRAWING 93 method of laying off these pressure lines is to join the center of the cam C with the center of each roll ; measure the angle which the line of pressure makes with this radius; and then transfer the angle to the proper point on the line of travel. This method is clearly indicated in the figure. As before, it will be seen that the line of pressure lies quite close to the line of travel, and therefore the cam will be an easy working cam. Example 5. Roll Follower Mounted on Oscillating Arm. 1. Follower Positions. In Fig. 83 the follower is a roll, as before; but Fig. 83. Diagram of Cam with Roll Follower on Oscillating Arm instead of traveling in a straight line, it is made to travel along the arc of a circle, being carried on the end of an arm OC, C being a fixed point about which the arm oscillates. The length of travel 06 is the same as before, and is likewise divided into six equal parts. This method of carrying the follower roll is, perhaps, the most com- mon of all, and is a very effective plan for giving the follower roll easy movement along its path. 94 MACHINE DRAWING 2. Cam Radii. The original radius CO is drawn in this case, as in all the others, through the original center of the follower roll. The radii CX and CB, limiting the arcs of rise, rest, and fall, are likewise drawn in the given relation to the original radius CO, and the arcs subdivided precisely as before. 3. Folloiver Rotation. For the purpose of follower rotation, arcs are now struck through the points 1,2,3, 4, 5, and 6, these arcs being prolonged until they meet the original radius in the points H, K, J, M, P, and Q. Then the rotation of the points H, J, K, etc., produces the intersections R v R 2 , R s , etc.; but it should be noted in this case that the follower roll, instead of getting ahead of the radius, as in Figs. 80 and 82, is lagging behind it at each position. The distances R 1 L V R 2 L 2 , R 3 L 3 , R±L V i? 5 L 5 , while being laid off equal to El, K2, J3, M4, P5, Q6, etc., as in Figs. 80 and 82, are laid off behind the radius in each position on the arcs of rise and fall. These distances are constantly increasing up to point 6, where the roll remains stationary during the period of rest, and then con- stantly decrease to zero, until the roll reaches the original position at point 0. From the points just found, arcs are struck as before, the radius being equal to the radius of the follower roll. 4. Tangent Line. The tangent line is drawn as a smooth curve to these arcs, and the arc of rest is struck as before, thus developing the outline of the cam. 5. Testing. The cams should be tested by the tracing-cloth method as before. 6. Pressure Line. The pressure lines are drawn precisely as in Figs. 81 and 82; but it is a little more difficult to rotate these pressure lines back to the points in the path of the follower, and the tracing-cloth method is suggested as best for this purpose. This is done by taking a scrap piece of tracing cloth, fixing a pin through it to the center of the cam, tracing upon it, from the paper below, the pressure lines and the centers of the follower. These centers being rotated back until coincident with the corresponding points of the travel, a second point in each pressure line is pricked through on the paper below. Upon the removal of the tracing cloth, each pressure line can then be quickly drawn through these pricked points and the corresponding centers of the follower, thus enabling the action of the cam to be properly judged. MACHINE DRAWING 95 Example 6. Pointed Follower Mounted on Oscillating Arm. In Fig. 84 the follower roll has been abandoned, and the original , pointed follower substituted. The motion of the follower point, however, instead of being in a straight line, is in the arc of a circle precisely as in Fig. 83, except that the follower, being a point instead of a roll, the points L v L 2 , L 3 , etc., have the outline of the cam drawn directly through them. This case is introduced merely for the Fig. 84. Diagram of Cam with Pointed Follower on Oscillating Arm purpose of making the set of cams complete, and it is so closely a counterpart of Fig. 83 that the detail study of it is considered un- necessary. Example 7. Flat Follower with Path Perpendicular to Working Face. 1. Follower Positions. In this example, Fig. 85, is introduced a follower with a flat surface, its path being perpendicular to its working face. The length of its path 06 is the same as before, and is divided into six equal divisions. 96 MACHINE DRAWING 2. Cam Radii. The point of original contact being chosen, the original radius OC is drawn perpendicular to it; the radii CX and CB, limiting the arcs of rise, rest, and fall, are then drawn in their proper relation to CO, and the arcs of rise and fall subdivided as before. 3. Follower Rotation. The intersections R v R 2 , R 3 , R v etc., Fig. 85. Diagram of Cam with Flat Follower Perpendicular to Working Face of the rotating arcs with the several positions of the radii, are found as before. The rotated positions of the follower in this case are obviously represented by drawing perpendiculars to the several radii through the points R v R 2 , R 3 , R 4 , etc. 4. Tangent Lines. The outline of the cam is produced by MACHINE DRAWING 97 drawing a tangent line to the several lines representing the rotated positions of the follower, the arc of rest being struck as before. 5. Testing. The cam should be tested by the tracing-cloth method. 6. Pressure Line. Pressure lines are drawn at the points of contact between the cam and the follower, by erecting perpendiculars to the face of the follower at these points. As in the case of the pointed follower, there is considerable friction due to the sliding of the cam along the follower face. This friction produces a side thrust perpendicular to the path of the follower, and modifies the pressure lines slightly. If it were not for this friction, the pressure line obviously would always be perpendicular to the follower face, acting at a point on the follower face some distance to one side of the original point of contact 0. By taking the distances R 1 U v R 2 U 2 , R 3 U 3 , etc., to the several contact points, and rotating them back, the manner in which the point of contact between the cam and the follower moves along the face of the follower during its travel can be conveniently studied; it is seen that the point of contact during the arc of rise moves to the right of the original radius, and gradually swings back again until, at the point 6, it is on the line of the original radius. During the arc of rest, the point of contact remains at point 6; during the arc of fall, it moves to the left of the original radius, finally coming back again to the original point of contact 0. Example 8. Flat Follower Mounted on Oscillating Arm. 1. follower Positions. In this example, Fig. 86, a flat-faced follower is carried by an oscillating arm similar to the roll in Fig. 83. The length of travel 06 is divided into six equal parts, as in the previous cases, the positions of the follower being indicated by the radial lines C'l, C% C'3, etc. 2. Cam Radii. The original radius CO is drawn through the assumed point of contact, and perpendicular to the face of the follower in its original position. [The radii CX and CB are then drawn limiting the arcs of rise, rest, and fall, and the subdivisions of the arcs of rise and fall properly made. 3. Follower Rotation. The intersections R v R 2 , R 3 , etc., of the rotating arcs are found as in the previous cases. The rotation of the follower is accomplished by drawing through the points R v R 2 , R 3 , etc., straight lines making the same angle with these radii as 98 MACHINE DRAWING the follower in its corresponding positions makes with the original radius CO. For example, the angle a x is equal to a; the angle b 1 is equal to b ; and the angle c 2 is equal to c. 4. Tangent Line. The tangent line is now drawn to the several positions of the rotated follower, and the arc of rest is struck, thus giving the outline of the cam. 5. Testing. The cam should be tested by the tracing-cloth method. 6. Pressure Line. The pressure lines are drawn the same Fig. 86. Diagram of Cam with Flat Follower on Oscillating Arm as in Fig. 85, and it is suggested that the rotation of them back to the positions of the follower in its path be accomplished by the tracing- cloth method, as in Fig. 83. Design of Complicated Cams. It should be especially noted, that in all the cases of cams thus far studied, the methods of pro- cedure are absolutely identical. In the more complicated cases of cams which follow, and others which may arise in the designing of MACHINE DRAWING 99 special machines, the same principles apply, however much they may apparently be disguised by the conditions of the problem. A good method to follow in designing a complicated cam is first to study the cam by the tracing-cloth method, as described on page 84. After an approximate outline of the cam has been determined as being possible, and giving about the motion of the follower desired, then the more formal method of rotating the follower about the cam can be applied, to give the exact outline. It should be remembered that it is not possible to reproduce by cam movements all combinations of length of travel, angle of rest, rise, and fall, as fixed by the con- ditions of the problem. In such cases . the cam is designed to give the nearest possible approach to the motion desired, or some of the working conditions are changed. In each of the cases considered, it has been assumed that the follower is always held against the surface of the cam, either by its own weight or by a spring. Another method of accomplishing this is to make a cam with two surfaces, the follower running between them in the groove thus formed. Plate Cams with Complex Motions Uniform Motion. All cams thus far considered are of the uni- form-motion variety, that is, having equal rise in equal time. This means that each fraction of the travel of the follower is made in the same time as each other similar fraction; and likewise, that each fraction of the rotation of the cam is made in the same time as that of any other fraction of its movement. In further explanation of the term "uniform motion", suppose, a railway train to travel ten miles in twenty minutes, the speed of the train being the same during each minute; it would travel J mile in each minute, and would have a uniform speed or velocity of \ mile per minute. Under such con- ditions the train would be moving at the full speed of \ mile per minute, both at the beginning and at the end of the ten miles. If, however, it had exactly ten miles to travel and exactly twenty minutes to do it in, and must be at rest at the beginning and at the end of the given time, it could not gain its full speed in an instant or lose it in an instant, but must start and stop gradually. There- fore, during the first part and the last part of the time, it would be moving at a speed slower than \ mile per minute, and must go faster than \ mile per minute during the middle part of the run, to make 100 MACHINE DRAWING up for the time lost in starting and stopping. Such motion would not be uniform. The more suddenly the train starts and stops, the more nearly uniform the main part of the travel may be, but the greater the shock when starting and stopping. Suppose we have a piece to be moved one foot in ten seconds; if the motion is to be uniform, the piece would have a velocity of T 1 o foot per second. If the piece is light and the mechanism which does the moving is sufficiently powerful, the piece may be made to start and stop almost instantly without serious shock, and consequently may have practically uniform motion. Variable Motion. If the mechanism which moves the piece be so designed as to start and stop it gradually, the shock will be avoided. We may have a gradual increase of speed at the start, until full speed is attained; then a uniform full speed during the main part of the stroke; and finally a gradual decrease of speed to a full stop at the end of the stroke; or the speed may increase during the entire first half of the stroke, and decrease during the entire last half, the motion at no time being uniform. The first condition is used where the piece is doing work during the stroke, as, for instance, the cutting stroke of a tool; and the second condi- tion, wherever quick motion is desired without regard to its Fig. 87. Harmonic Motion Diagram" character, SO long as it is without shock. Harmonic Motion. In Fig. 87, let the semicircle ABD repre- sent the path along which a piece moves with a uniform velocity. Now, if we have another piece moving along the diameter AD, starting from A at the same time as the first piece, and moving at such speed that a perpendicular let fall from any position of the first piece to the line AD will locate the second piece — that is, when the first piece is at C, the second piece is at E; when the first piece is at B, the second is at 0; and so on — then the piece which travels along the line AD has harmonic motion. It moves slowly at first, increases to a maximum speed at the center, and decreases to rest at the end. This motion is quite common for shaper rams, slotters, and feed- mechanisms. Cams can readily be designed to give such a motion. O E MACHINE DRAWING 101 Uniformly Accelerated and Retarded Motion. A piece which has uniformly accelerated and uniformly retarded motion (see article on Mechanism) moves through one unit of space in the first unit of time, three the second, five the third, seven the fourth, nine the fifth, etc., to the middle of its stroke, then decreases at the same rate to the end of the stroke. For example, if a piece is to move with uniformly accelerated and retarded motion one foot in ten seconds, it will move -§-V foot the first second, •§%- the second, /$ the third, j\ the fourth, 5V the fifth, when it will have traveled jV+so +ro + tt+ttV ( = If)j or \ the whole foot in one-half the whole time, the speed increasing all the time; at the end of the fifth second, when half the distance has been traveled, it begins to slow down, and travels 5V the sixth second, T \ the seventh, yV the eighth, -gV the ninth, and •o the tenth. The rate at which the velocity increases during the first half of the time is often made the same as that at which the velocity of a weight increases when dropped from a height; and the rate at which the velocity decreases during the last half of the time, the same as that at which the velocity of a weight decreases if thrown straight up into the air. This particular form of uniformly accelerated and uni- formly retarded motion is, therefore, known as gravity motion. It is commonly produced by cams, although not often used for motions greater than a few inches. If in Fig. 79 it had been required to raise and lower the follower with harmonic instead of uniform motion, the only difference in procedure would have been in dividing up the path 06. The divi- sions of 06, instead of being equal, would be found as shown in Fig. 88. Suppose the line Ae to be the same length as 06; on this line as a diameter, draw a semicircle, and divide this semicircle into as many equal parts as the arc of rise is divided. In this case, suppose the arc of rise to be divided into 8 equal parts; then the semicircle is like- wise divided as shown in the figure. From the points B, C, D, etc., drop perpendiculars to the line Ae, cutting it at points 1, 2, 3, etc. For the first eighth of the arc of rise of the cam, let the follower rise Fig. 88. Semicircle Show- ing Harmonic Steps 102 MACHINE DRAWING the distance A-l, for the second eighth the distance 1-2, for the third eighth the distance 2-3, and so on. Such motion of the follower is harmonic motion. If it is required that the follower shall rise and fall with uniformly accelerated and retarded motion, the method of dividing the line of travel Ae is shown in Fig. 89. As in the case of harmonic motion, suppose the arcs of rise and fall each to be divided into 8 equal parts. Now, the line Ae must be divided into 8 parts, but these parts must be such that, beginning with the point A, the distances A-l, 1-2, 2-3, and 3-4 shall be in the ratio of 1, 3, 5, and 7; and the distances 4-5, 5-6, 6-7, and 7-e shall be in the ratio of 7, 5, 3, and 1 ; in other words A-l is 3V of the whole line Ae; 1-2 is s 3 j of Ae, 2-3 is -$j of Ae, and so on. To divide up the given length Ae so that the divisions may bear the above relation to one another, draw the line Ar at any con- , venient angle, and, choosing /r H any convenient distance as a unit, mark it off on this line 32 times, beginning at A. From I, the last of these dividing points, draw a line to e; next find the point B, the first division from A; C the third from B, D the fifth from C, E the seventh from D, F the seventh from E, G the fifth from F, H the third from G; and through the points H, G, F, E, etc., draw lines parallel to Ie, cutting the line Ae at 7, 6, 5, 4, etc. It is obvious that Ae is then divided in the same proportion as A I, and if the follower were of g bividin g Line made to travel along the line Ae according to these of Travel . . . divisions, it would have uniformly accelerated and retarded motion. Practical Example of Complex Motion Cam. For the purpose of illustrating these principles, suppose it is required to design a plate cam, Fig. 90, such that the follower rises from point A to e, with harmonic motion, while the cam rotates through 120°; it is then to remain at rest during the cam movement of 60° ; it is then to fall to its original position with a uniformly accelerated and retarded motion, while the cam turns through 150°; it is then to remain at rest while the cam rotates through the remaining 30°, when the same MACHINE DRAWING 103 cycle of movement is to be repeated as long as desired. This is briefly expressed as follows: Harmonic rise 120° Rest 60° Uniformly accelerated and retarded fall 150° Rest 30° 1. Follower Positions. The length of travel Ae being known, it is divided for purposes of the rise, by the principles of Fig. 88, into Fig. 90. Diagram of Complex Motion Plate Cam distances giving harmonic motion of the follower; and for purposes of the fall, by the principles of Fig. 89, into distances giving uniformly accelerated and retarded motion. Eight spaces are chosen, so that the process of making these divisions is an exact repetition of the method in Figs 88 and 89. 104 MACHINE DRAWING 2. Cam Radii. The diameter of the base circle being chosen, and, for the purpose of this problem, the center being assumed in line with the path of the follower, draw the original radius CA, then the radii CX, CZ, and CW, limiting the arcs of rise, rest, and fall respectively. As 8 divisions of the follower path have been chosen, the arcs of rise and rest must each be divided into 8 equal divisions. It should be observed that while the divisions are equal throughout each arc, the arc of fall being different from the arc of rise, the divisions of the arc of fall are not equal to the divisions of the arc of rise, measured on the base circle. 3. Follower Rotation. The rotation of the follower about the cam, for the period of rise, is accomplished by striking arcs through the points 1,2,3, 4, 5, 6, 7, and e, making the intersections R lf R 2 , R 3 , R 4 , R 5 , R Q , R 7 , and R 8 , with the cam radii. The rotation of the fol- lower about the cam, for the period of fall, is accomplished by striking arcs through points V, 2', 3', 4', 5', 6', 7', and e, making the inter- sections F v F 2 , F 3 , F 4 , F h , F Q , F 7 , and F 8 , with the cam radii. These points of intersection represent the centers of the follower roll in its rotated positions, and from these centers should be struck arcs with a radius equal to the radius of the follower roll. 4. Tangent Line. A smooth curve is now drawn tangent to these small arcs, thus forming the outline of the cam. 5. Testing. The cam may be tested by the tracing-cloth method, precisely as in the cases already developed. 6. Pressure Lines. The pressure lines are found in exactly the same manner as in Fig. 81, and can be rotated back to the points in the path of the follower, in order to conveniently study the change in direction of the pressure lines as the follower moves along its path. It should be noted that in Fig. 90 the same method of procedure is followed as in Figs. 79 to 86, except that the determined points in the path of the follower do not make equal divisions of the path, as in the case of uniform motion. Translation Cams Rotating plate cams, like those thus far considered, are most commonly met with in practice. A straight-line, reciprocating motion of a plate, however, may be made to produce similar follower movements, in which case the cam is known ^s a translation cam. A straight-line movement is equivalent to movement along an arc MACHINE DRAWING 105 with infinite radius. With this understanding, the same principles may be made to apply to translation cams as to rotating cams. Development of Translation Cam. Suppose it is required to produce the same movement of the follower as in Fig. 90, by means of moving a plate in a straight line instead of rotating it. This case is shown in Fig. 91. 1. Follower Positions. The same follower motion being required as in Fig. 90, the path is laid out exactly in the same way, the follower positions for the rise along path D8 fulfilling the require- ment of harmonic motion, and for the fall along path IF 8 , fulfilling the requirements of uniformly accelerated and retarded motion. This is shown in the figure, and it is observed that no change from the method of Fig. 90 is employed. 2. Cam Radii. The base circle does not exist in this case as a circle, but has become a straight line, and may be chosen of any length, say Dx. The cam radii, being always perpendicular to the /' m' it p' r' S' t' u' v' Fig. 91. Diagram Showing Development o f Translation Cam cam arc (in this case the straight line Dx), become parallel lines, perpendicular to Dx. The cam arc of rise in Fig. 90 is now repre- sented in Fig. 91 by the distance D8, which should fulfill the relation ^ft~ = ttwx ; in order to make the same relative movement of cam dur- Dx 350 ing rise as in Fig. 90, Dk should likewise be divided into 8 equal parts. The arc of rest in Fig. 90, being \ the arc of rise, the distance hi in Fig. 91 is made \ the distance Dk. The arc of fall in Fig. 90 being 1J the arc of rise, the distance h in Fig. 91 is made \\ the distance Dk. The final arc of rest in Fig. 90 being \ the first arc of rest, the distance v x in Fig. 91 is made J the distance hi. This completes the cycle; and the parallel lines aa' ', W, cc' ', etc., drawn through the 106 MACHINE DRAWING several points of division as noted, represent the several positions of the cam radii. 3. Follower Rotation. Since the lines of follower rotation arc all perpendicular to the cam radii — which in this case are all parallel — the rotation, or translation, of the follower is accomplished by draw- ing parallel lines through the determined points of the path, pro- ducing the intersections R v R 2 , R 3 , R 4 , etc. Between points R 8 and F 8 , the follower rests; and for the period of fall, the intersections F 8 , F 7) F Q , F 5f etc., are determined as for the rise, by producing the parallel lines through the points in the path of fall. From point v to x the follower again rests. These intersections represent the centers of the follower in its translated positions. Now, with a radius equal to the radius of the follower roll, arcs are struck to represent the outline of the follower in each of its trans- lated positions. 4. Tangent Line. A smooth curve is now drawn tangent to the several translated positions of the follower roll. In this cam a new feature is introduced by drawing these tangent lines on both sides of the roll, thus making a groove which holds the follower firmly in position at all times. This gives an absolutely positive fall to the follower roll. The same grooved construction might have been made on any of the cams heretofore studied, instead of allowing the fol- lower to come down by gravity or by the force of a spring. 5. Testing. The cam may be tested by the tracing-cloth method as before, the procedure in this case, however, being one of translation instead of rotation. The original radius, with the fol- lower in its several positions being traced upon the cloth, is set upon each of its translated positions, and, by careful inspection, it is noted whether the roll, in this position, just touches the faces of the cam groove as drawn. 6. Pressure Line. The pressure lines are drawn precisely as in all cases thus far considered, and may be translated back to the path of the follower in order to study their direction as the follower moves along its path. Although the same cycle of follower movement has been accom- plished in this case as in the rotating cam, Fig. 90, the translation cam is not in position to begin a repetition of the cycle by further movement. If we reversed the motion of the cam, the cycle also MACHINE DRAWING 107 would be reversed; and in the cam under discussion we should have a rest, then a uniformly accelerated and retarded rise, then a rest, then a harmonic fall, the periods of time being reversed as well as the motion. We could, of course, by choosing the motion for rise and fall exactly the same, secure the same motion for the reversed as for the forward movement of the cam. Cylindrical Cams Development of Cylinder Cams. Suppose that the outline of the translation cam as developed in Fig. 91 be wrapped around a cylinder whose circumference is exactly equal to Dx, and that the lines represent a spiral groove cut into the surface of the cylinder. If, then, a follower roll be allowed to remain in this groove while the WIDTH OF PLATE=LEHGTH OFCYL Fig. 92. Development of Cylindrical Cam cylinder is rotated on its axis, the cycle of follower movement will be repeated as long as we choose to rotate the cylinder. Such a grooved cylinder is known as a cylindrical cam. Fig. 92 shows a cylindrical cam in two projections. Attention is called to the tapering follower roll used. This is because it is necessary that points on the sides of the groove and the surface of the roll have the same velocity about the center C. The roll, there- fore, must be the frustum of a cone whose apex is at C. The top of this groove is produced by wrapping Fig. 91 around the surface of the cylinder as previously described. The bottom of the groove is produced by making a translation cam whose base line is equal in length to the circumference of the cylinder at the bottom 108 MACHINE DRAWING of the groove, and then wrapping it around that cylinder. This base line for this smaller cylinder is divided into the same number of parts as the line Dx, the divisions, however, all being proportionally smaller. The length of the follower path, and its divisions, are in nowise different from those shown in Fig. 91; and the method of developing the outline of the cam is precisely the same. The wrapping of these translation cams, for purposes of the drawing, is accomplished by means of dividers and compasses, according to the principles for the development of cylinders, as explained in Mechanical Drawing, Part III. The limitations of construction of cylindrical cams are consider- ably greater than those of the simpler rotating cams; and it is more frequently a question of experiment and trial to get the proper sur- faces, than it is of exact theoretical layout on the drawing board. BELTING Cams and gears transmit positive motion from the driver to the follower by direct contact of the surfaces. As the distance between ± X i CENT RAY- PLANE i ! Y ; [ ck A B Fig. 93. Diagram of Simple Open Belt Drive centers of shafts increases, the driver and follower for such methods of transmission become large, unwieldy, and costly, and rigid links may be used to connect the rotating pieces, as in the case of parallel MACHINE DRAWING 109 rods of a locomotive. For a further increase of distance, the trans- mission is attained by means of belts and pulleys, and, if the distance is very great, by wire ropes and sheaves. As there is always some slipping of the belt (from 1 to 2 per cent), the velocity ratio is not exact; but this is not essential in many classes of machinery. The slip and stretch of the belt reduce the shock when heavy machinery is set in motion — an important feature in many cases. Open and Crossed Belts. The simplest forms of belt drives are the open belt (Fig. 93) and the crossed belt (Fig. 94). In each Fig. 94. Diagram of Simple Crossed Belt Drive case the shafts are parallel, and the pulleys fastened to the shaft with set screws or keys. The central planes of the pulleys must obviously be coincident. The belt is then tightly stretched over the pulleys, and, assuming B, the driver, to turn in the direction of the arrow, motion will be transmitted to A, on account of the friction set up between the belt and pulley surfaces. The fibers of the belt, in running on or off the pulley, bend over one another, so that those next the pulley, on the inside of the belt, are compressed, while those on the outside are stretched. Assuming the compression and stretch to be equal, then the central fiber does not change in length. This central fiber is shown in the figure by a "dash-and-dot" line. Con- sidering that there is no slip of the belt on the pulley, the face of each 110 MACHINE DRAWING pulley will move exactly with the belt, and the turns of each pulley will depend on its circumference; or, Speed of belt S Turns of A = Turns of B = Velocity ratio = Circumference of A 7TX Diameter of A Speed of belt S Circumference of B ~~ tt X Diameter of B Turns of A Diameter of B Turns of B Diameter of A Thus the velocity of the shafts is inversely proportional to the ratio of the diameters of the pulleys. The action of the belt in bending about its central fiber has the effect of increasing the diameter of the pulley by an amount equal to the thickness of the belt, and an exact calculation for velocity ratio must take this fact into consideration. For example, suppose that the diameters of A and B are 8" and 24" respectively, and that the belt is \" thick. Then the velocity ratio 24 . 24.25 is -77- = 3 for the usual approximate calculation; but Q ' =2.939 for the exact value. The direction of shaft rotation depends on the method of apply- ing the belt. In the case of the open belt, the top surfaces of each pulley being connected, each shaft rotates in the same direction; while in the case of the crossed belt, the top surface of A being connected to the bottom surface of B, the shafts rotate in opposite directions. Thus the directions of rotation are the same when the center line of belt lies wholly on one side of the line connecting the centers of pulleys; and different when it intersects the line of centers. Crowning Pulleys. Suppose that a flat belt is placed on the side of a double cone, Fig. 95, and that w T e start to rotate the cone in the direction of the arrow. The edge E, which is stretched more tightly than F, has a greater grip on the surface of the cone, and will climb up the incline as shown by the dotted lines. With continued rotation of the cone, the belt, if not prevented, will move farther up the incline, will finally pass the crest, and start down on the other side until the two edges E and F have equal tension, or the pull to the right is balanced by an equal pull to the left. The center line of the belt will now run in the central plane X Y of the pulley. As long as this condition is maintained, the belt will run true and will stay on the pulley. Also, if the pulley faces were perfectly MACHINE DRAWING 111 flat, the belt a perfectly homogeneous piece of leather, and the shafts perfectly parallel, the belt would stay in the pulley. Such perfect conditions, however, cannot be produced or maintained, and it is therefore necessary in practice to imitate the conditions of Fig. 95, and "crown" either one or both pulleys, so that the belt will not develop any tendency to run off. On the contrary, it will constantly seek to keep its center line in the central plane of the pulleys, any tendency of one edge to slacken and run off being instantly counter- acted by the tightening up of the other as it starts to climb, thus pulling the belt back until the balance is secured. A very slight amount of crowning will accomplish this result, and as little crown as possible, consistent with good running, should be provided, that too great inequality of tension in the belt may not be intro- duced. In Fig. 93, if the shafting be not parallel, the center line of the belt will not run in the central plane of the pulley, and the belt will climb towards the high part of the pulley, as in the above case of the cone, and we may expect the belt to run off. The above discussion reduces to one funda- mental working condition for belt transmission, viz, The center line of the belt leaving a pulley must lie in the central plane of the pulley to which the belt is delivered. This principle is applicable to all cases of belt transmission, however complicated, whether the shafts be parallel or at an angle. The use of guide pulleys is merely a means of controlling the delivery of the belt according to the principle. The student should commit this principle to memory, and go over its application until he is sure that he understands it; for without it he cannot solve complicated belt problems, and he cannot feel sure of his solution of even the simplest ones. In the pages of discussion and illustration which follow, the student should constantly note the recurrence and application of this principle, as it is really all there is to the solution of belt problems, except familiar knowledge of how to make the drawing projections, which he already is supposed to possess. Fig 95. Theory of Crowning a Pulley 112 MACHINE DRAWING Tight and Loose Pulleys. Tight and loose pulleys are provided for cases in which a machine is to be thrown in and out of service without stopping the driving shaft. A common arrangement is shown in Fig. 96, where a pulley with a straight face is located on the line shaft, and two pulleys with crowned faces are on the countershaft. Pulley B is loose on the shaft, and C is fast to the shaft. A collar D is placed on left of B, to prevent its end motion. Shifting the belt is accomplished by pushing on the advancing side of belt, close to the receiving pulley. Fig. 96. Diagram of Tight and Loose Pulley Drive The shifter F has two iron pegs, one on each side of the belt, and is operated by hand. The belt is readily guided by pressure on the advancing side, for the motion of the receiving pulley aids the motion of the belt; but if pressure were applied to the retreating side it would be necessary to use enough force to shift the belt bodily sidewise on the face of the pulley. As excessive tension on the belt decreases its life, the diameter of the loose pulley is often slightly de- creased, thus permitting the belt, when doing no useful work, to be under less tension than when driving. MACHINE DRAWING 113 ^^~ Another arrangement is to provide a clutch to throw into a loose pulley on the line shaft, the belt standing idle when not in service. Shafts Not Parallel. Suppose an open belt to connect pulleys A and B v on parallel shafts, Fig. 97. Draw a tangent XY to the pitch circles of the pulleys at the points L 1 and L 2 , where the belt leaves the pulleys. Now rotate the central plane of the pulley B v about X Y as an axis, through any angle C, to position shown by pul- ley B. The central planes (shaded) of pulleys A and B intersect on the line X Y, called the trace of the planes. The axes are now not parallel, but the belt may be made to run in one direction, for it still obeys the general principle of the guiding of belts; i.e., the center line of the belt, on leaving the driving pulley, is delivered into the cen- tral plane of the receiving pulley. Examining the figure, we find that the center line of the belt moves in direc- tion of arrow from L 1 to R, and around pulley B to L 2 , from L 2 on the surface of B to R 2 , thence on surface of A to L v the starting point. From the point L v where the belt leaves A, until it reaches R, the center line of the belt is in the central plane of j the receiving pulley B, and the Fig. 97. Diagram of Pulley Drive where Shafts Are not Parallel 114 MACHINE DRAWING belt twists about this line, presenting a flat side to the face of pulley B at R. From L 2 , where the belt leaves B, until it reaches i? 2 , the center line of the belt is continually in the central plane of the receiving pulley A, and a similar twist in the belt takes place. If now we attempt to reverse the direction of motion of the belt, the top of pulley A, moving in the direction of the dotted arrow, would carry point D of the center line of belt to the left-hand edge of A, as indi- cated by the dotted line DE, where it would drop off. Therefore, this belt drive for shafts not parallel is suitable only for motion in one direction. Quarter=Twist Belt. By rotating the cen- tral plane of B, Fig. 97, until the angle C be- comes 90°, a quarter-twist, or half-crossed belt, Fig. 98, is obtained; and if angle C becomes 180°, the crossed belt of Fig. 94 is the result. If the thickness of belt is neglected, it will be noted that the central plane of B (Fig. 98), which is represented by the trace XY, is tangent to the surface of pulley A; and similarly on the side view, the trace ST oi the central plane of A is tangent to the surface of B. Now follow the center line of belt in the direc- tion of the arrows on the front and side views, starting at point A, where the belt leaves the upper pulley. From A to J), and around to the back of pulley B, the center line is shown in the trace XY of the front view. From B, where the belt leaves the lower pulley, to c, and around to the front and starting point A, the center line is shown in the trace ST oi side view. Therefore the center line of the belt is always delivered into the central plane of the receiving pulley, and it will drive satisfactorily in the direction of the arrows. Reversing Fig. 98. Diagram for Quarter-Twist Belt MACHINE DRAWING 115 the motion will cause the belt to run off the pulleys, as in the pre- vious case. The belt should always be put on so that the same side of the belt touches both pulleys when it is possible to do so. In making the drawing of the belt we shall call the side of the belt which touches the pulleys the inside, and the other side the outside. Now, referring first to the left-hand elevation in Fig. 98, where the belt lies around the circumference of the upper pulley, from the point c, where the upward-moving part of the belt strikes the pulley, around to A, where the downward-moving part leaves the pulley, only the edge of the belt is visible, and is represented by drawing an arc of a circle from line oc around to oA, with a radius equal to the radius of the pulley plus the thickness of the belt. The location of c may be found closely enough for all practical purposes, by drawing a line from B tangent to the upper pulley, c being the point of tangency, and oc the radius drawn through c. In drawing the arc of the circle from oc to oA, it is well to let it run by these lines a little way in the pencil drawing, and that part which is not used may be erased after the drawing is inked. The descending part of the belt leaves the pulley at A; and from that point to the place where it strikes the lower pulley, it twists through an angle of 90°, coming out over the front of the lower pulley. The edge of the belt, which we see in its full thickness where it leaves the upper pulley at A, twists toward the left, less and less of it being seen as the belt descends, until at d, where it strikes the other pulley, the two corners of this edge coin- cide, and from there to the bottom of the pulley we see this edge of the belt as a line. At the same time that the thickness of the belt has been disappearing from view, the outside of the belt has been coming into view, until at dd' we see the full width of the belt, the outside corner being the one which is visible. The inside corner is behind the rest of the belt, and while it may be shown dotted in the drawing, it is usually omitted entirely. From d' to the bottom of the pulley the two right-hand corners coincide. Points d and d' are found by drawing the horizontal dotted line through D (side view), and laying off on this line a distance equal to one-half the width of the belt each side of line XY. From ee' the belt goes around the back side of the pulley to W, where it begins to be drawn off to the left, W being on the center line drawn through 116 MACHINE DRAWING the shaft, since, by glancing at the right-hand view, we can see that the upward-moving part of the belt leaves the lower pulley at B, which is on a level with the center of the shaft. After leaving bb' ', the belt remains behind the pulley for a short distance, and is shown dotted. It is projected at its full width at bb' y but as soon as it leaves the pulley it begins to twist toward the right, the left-hand edge gradually coming into view until it is seen at its full thickness where it strikes the pulley at C. At the same time, the inside face of the belt, which is toward the front when the belt leaves the pulley, gradually turns toward the right, and appears narrower until it disappears from view — that is, projected as a line. This completes the front view, and the side view is drawn according to the same principles, as is also the plan view. To be strictly correct, the sides of the belt should be shown curved at A and B, for the belt is pliable and starts to curl and slip sidewise a short distance above these points. In order not to have an exces- sive side slip, the angles c B A and DAB should not be more than 25°. Figs. 99 and 100 show what changes are made in the location of the pulleys and the appearance of the belt by changing the direction of rotation of the shafts. In Fig. 99 the lower shaft turns in the same direction as in Fig. 98, but the upper shaft turns in the opposite direction. In Fig. 100 the upper shaft turns in the same direction as in Fig. 98, and the lower shaft turns in the opposite direction. Reversible Quarter=Twist. Two Guide- Pulleys. In order to reverse a quarter-twist belt, it will be necessary to introduce one or two guide-pulleys to bring the center line of the belt at all times into the central plane of the receiving pulley. Fig. 101 shows an Fig. 99. First Variation from Fig. 93 for Quarter- Twist Belt MACHINE DRAWING 117 arrangement where two guide-pulleys are used. Let the driving pulley R and the driven pulley P be located as in the case of the quarter-twist belt of Fig. 99. Suppose that the direction of rotation is but seldom reversed, and that the usual motion of the driver is in the direction of the arrow. The part of the belt which has the greater load should have a direct connection between R and P, leaving the slack side to run over the guide-pulleys, thereby decreas- ing the stress on the belt and lessening the fric- tion in the journals of the guide-pulleys. Receiving point A is then connected to B, the point of departure from the back of the driven pulley, instead of over to the front face, as in case of Fig. 99; and the belt twists about this line as an axis through an angle of 90°, so as to present flat sides to both pulleys. The plan view of the center line of the belt is the line of intersection AB of the traces of the cen- tral planes of R and P. Evi- dently the belt will run in either direction along the trace of either plane. From the point of departure D of the driving pulley, the belt must be led to the receiving point E of the driven pulley, by means of guide-pulleys. Draw BE for the plan view of the central plane of the guide-pulleys. This plane is perpendicular to the paper, and its traces or intersections with the central planes of R and P are shown in X Y and DH of the front view. The guide-pulleys are idlers introduced only to form a path for the belt, and do not in any way affect the velocity ratio. They may, therefore, be made of any convenient size to suit the existing conditions. We may then assume on the plan view, that J and K are points on the axes of the pulleys M and N, and draw the guide- pulleys so that the face of M bisects the front face of P at E, and Fig. 100. Second Variation from Fig. 98 for Quarter- Twist Belt 118 MACHINE DRAWING one face of N bisects the right-hand face of R at D. On the front and side views, the location of the axes has been assumed as GG and FF, and the corresponding views of the pulleys are drawn according to the principles of projection. Examining the belt in passing from D to E, we find its center line goes from D in the central plane of R, to H in central plane of N, around N and M, which Fig. 101. Reversible Quarter-Twist — Two-Guide Pulleys have one common central plane, arriving at C, a point in the trace of the central planes of M and P, and from leaving point C to receiving point E. It will be noted that the center line of belt connecting both leaving and receiving points* is always in the cen- tral planes of both pulleys, and, therefore, the direction of motion may be reversed at will. If the belt be followed around the pul- MACHINE DRAWING 119 leys, we find both sides of the belt come, successively, in contact with the pulleys. Therefore, the belt must be given a single twist before uniting the ends together. It is usually desirable to have only one side the working side; but if such were the case in this arrangement of pulleys, it would bring a sharp twist in the belt, between M and N, which might be a greater objection. One Guide- Pulley.* Fig. 102 shows the arrangement of the pulleys for the belt to run in either direction, using only one guide- pulley. The ordinary direction of rotation is that shown by the arrows. The upper pulley is the driver, and, as in the case where two guide-pulleys are used, the tight part of the belt goes directly from one main pulley to the other, the slack part of the belt returning over the guide-pulley. The shaft of the guide-pulley must be set at an angle with both main shafts in order to guide the belt properly. The method of locating the main pulleys is exactly the same as in the case where the two guide-pulleys are used, so that the explanation given for that case will apply here, and all we need to consider in this case is the location and drawing of the guide-pulley. We shall first consider the two elevations. The plumb line X Y, as well as being the center line of the tight part of the belt, is the line of intersection of the central planes of the two main pulleys. Choose a point in the line X Y, which may be anywhere along the line, depending on how far the guide-pulley is to be from one or the other of the main shafts, but preferably about half-way between them. The point is marked M h in the left-hand elevation, and M v in the right-hand elevation. From M h draw a line tangent to the upper pulley at D h , and from Ji| draw a tangent to the lower pulley at E\ The other projection of the line 2I h D h will be M V B\ coinciding with XY in the right-hand elevation; and the other pro- jection of M V E° will be M h E h , coinciding with X Y in the left-hand elevation. We now have two lines, M D and ME (shown respectively by their two projections, M v D v —M h D h and M v E v —M h E h ) l which determine the plane of the guide-pulley and which are practically the center lines of that part of the belt which passes over the guide- pulley, and our problem is one of projections. The problem is to *This section is optional. 120 MACHINE DRAWING find on the drawing paper the traces of the plane which contains the two lines, which is the central plane of the guide-pulley, and revolve Fig. 102] Reversible Quarter-Twist — One Guide Pulley this plane about one of its traces until it is parallel to the plane of the paper, so that the true angle between the lines will be shown; MACHINE DRAWING 121 then draw the guide-pulley tangent to the lines in their revolved position, and revolve the lines back to their former position, revolv- ing the guide-pulley back at the same time. To carry out this construction, proceed as follows: Draw a ground line anywhere between the two elevations, parallel to X Y ; and, for the time being, consider one of the elevations as a horizontal projection and the other as a vertical projection, remembering that our drawing is made as if projected on two planes located as in Fig. 2, Machine Drawing, Part I, or, as it is commonly expressed, "in the third quadrant". We shall treat the left-hand elevation as if it were the horizontal projection, and the right-hand elevation as if it were the vertical projection. Extend line M h D h until it meets the ground line at d h ; and at d h draw a perpendicular to the ground line, meeting XY (which is the same as M V D V extended) at d v . Through d v draw a line parallel to M V E V ; and this line, which is marked VP, is the vertical trace of the plane which contains the lines MD and ME. In like manner find the horizontal trace by extending M V E° to meet the ground line at e v , erecting a perpendicular at e v to meet M h E h at e h , and drawing HP through e h parallel to M h D h . If the work is cor- rectly done, HP, VP, and the ground line will intersect in a common point. Now through M h draw a line perpendicular to HP, meeting HP at p. Construct the right triangle tm h P (Fig. 103), making m h P equal to M h p on Fig. 102, and making m h t equal to the perpendicular distance of M v from the ground line in Fig. 102 (that is, equal to cM v J. Then take the distance Pt (Fig. 103) and lay it off on the line pM h (Fig. 102) from p, thus obtaining point N. ' Join N and e h , and through N draw Ng parallel to M h D h . The lines Ne h and Ng are the projections on the horizontal plane of lines ME and MD, respectively, when the plane P, which contains these two lines, is revolved so that it is parallel to the horizontal plane. Therefore the angle g Ne h is the true size of the- angle between lines ME and MD. Now, with a radius equal to the radius of the guide-pulley which is to be used, draw a circle which shall be tangent to the lines Ne h and Ng. This circle is the central circle of the guide-pulley revolved parallel to the horizontal plane, and its center S is the revolved position of the center point of the guide-pulley, and, of course, lies in the plane P. To revolve the central circle of the guide- pulley back so as to get its two projections when it is in the position 122 MACHINE DRAWING which it actually occupies with relation to the two main pulleys, we shall first revolve the point S back to h . To do this, draw SK perpendicular to HP. Then in Fig. 103, lay off from P along the line Pt the distance PV, equal to SK in Fig. 102. Care must be taken to lay off this distance from P rather than from t; and in order to remember from which point to measure, the student can bear in mind that distances measured along the hypotenuse from P (Fig. 103) represent distances measured from HP (Fig. 102). Having thus found point V, draw a line perpendicular to m h P, meeting it in o h ; take distance o h P in the dividers, and lay it off from K along KS (Fig. 102), thus getting h . Then point h will be the center of the ellipse which repre- sents the center circle of the guide-pulley in its actual position. Point 2, where KS cuts M h D h , will be one end of the the minor axis, and point 1, found by laying off h l equal to h 2, will be the other end of the minor axis. The major axis is . found by drawing a line through h parallel to M h D h , and laying off along this line ^airLKr/of from h the distances h 3 and 0% each equal to the radius of the guide-pulley. Having now found the two axes of the center ellipse, it can be drawn by any geometric method for constructing an ellipse. We shall next find V by prolonging the major axis of the ellipse just found until it meets the ground line at o 2 , then erecting a per- pendicular to the ground line at o 2 to meet VP at o 3 , drawing a line through o 3 , parallel to the ground line, and from h drawing a line perpendicular to the ground line which will meet the parallel through o 3 at V . This point will be the vertical projection of the center of the middle circle of the guide-pulley. The ellipse, which is the vertical projection of this middle circle, is found from V in a way exactly similar to that in which the ellipse for the horizontal pro- jection was found from h . The next step is to draw the guide-pulley and its shaft, and to do this we shall revolve the central ellipse over in each view in such a way that we shall have it projected as a line. We shall take the horizontal projection first. Extend the major axis of the ellipse from h to o 4 , making O h o 4 equal to the perpendicular distance of MACHINE DRAWING 123 O v from the ground line. Draw 6 1 through point 1 parallel to O^o 4 . With o 4 as a center, and with a radius equal to the radius of the guide-pulley, cut o Q l at o 6 , and cut D h M h extended at o 5 . Points o 6 , o 4 , and o 5 will be in a straight line, and the line joining them will be the edge view of the central circle of the guide-pulley. About this line o 6 o 5 draw a rectangle as shown, the width of the rectangle being made equal to the width of the face of the guide-pulley. Through o 4 draw a line perpendicular to o 6 o 5 , which will be the revolved posi- tion of the center line of the guide-pulley shaft. The method of revolving back to get the axes of the ellipses, which are the projec- tions of the edges of the pulley in its actual position, and to get the projection of the shaft, will be clear from a careful study of the figure. The vertical projection of the guide-pulley is found by revolv- ing over in exactly the same way, the distance (To 1 being equal to the perpendicular distance of h from the ground line. It is well to assume a definite length for the shaft, whether this be the actual length which the shaft would have or not. The length assumed in the figure is T X T 2 (same as T 3 T 4 ), and half of this is laid off each side of o 4 in the revolved horizontal projection. This completes the two elevations of the guide-pulley. The plan is drawn as follows: Find the projection LL of the two ends of the shaft as shown by the construction lines; then revolve over by drawing line KK 1 at any convenient place parallel to LL, draw- ing perpendiculars through the points LL, meeting the parallel line at K and K 1 , and laying off on these perpendiculars the distances K^L 1 and KL 2 , equal respectively to L D P D and L E P E in the ele- vation. The line L 1 L 2 , joining the points L 1 and L 2 thus found, is the revolved position of the shaft, and should be equal in length to TT and ff in the elevations. We can now draw the rectangle which represents the revolved position of the guide-pulley at the middle of the line L 1 L 2 , and find the ellipses from this rectangle in the same way as we found the ellipses from the rectangle in the other two views. The belt is drawn in accordance with the same kind of reasoning as was used in determining the way the belt would look in the other kinds of quarter-twist belts which we have studied. 124 MACHINE DRAWING fJ- R Belts Connecting Shafts in Same Plane But Not Parallel. It very often happens that a belt must connect two shafts which are on the same level, but which are not parallel. The connection can be made, whatever the angle between the shafts, by the use of two guide-pulleys. If the two main-shaft pulleys are of the same diameter, the belt may be made to run in either direction by putting both guide-pulleys — or mule pulleys, as they are often called — on the same shaft, which will be perpendicular to the plane containing the axes of the main shafts. That is, if the main shafts are horizontal, the shaft for the guide-pulleys will be vertical. If the main pulleys are of different diameters, the guide-pulleys may still be placed on the same vertical shaft, but in this case the belt can run in only one direction. If the belt is to run in either direction, the guide-pulleys are placed on sepa- rate shafts, which are usu- ally adjustable in position, so that they may be tipped at the proper angle to re- ceive and deliver the belt. We shall first take the case where the two main pulleys are of the same size. Fig. 104 shows the arrangement, the upper view being the plan, and the lower view, the elevation. R and S are the two main pulleys, and C and D are the two guide-pulleys. The line X Y is the line of inter- section of the planes of the main pulleys. The location of the guide-pulleys is sufficiently clear from the drawing, without further explanation. Fig. 105 shows the arrangement when the main pulleys are of different diameters. Here the pulleys can turn only in the direction shown by the arrows; for if the direction were reversed, the belt would leave the pulleys. The pulleys in plan appear the same as Fig. 104. Belt Drive for Same Sized Pulleys, Shafts not Parallel but in Same Plane. MACHINE DRAWING 125 M*» in Fig. 104. In the elevation, the upper guide-pulley, which receives the belt from S, has its central plane tangent to the pulley S at the point where the belt leaves S, as shown by the line A V B V . The lower guide-pulley, which receives the belt from R, has its center plane tangent to R, as shown by C V D V . If the pulleys were to turn in the opposite direction, the upper guide-pulley would have its plane tangent to R, and the lower one, its plane tangent to S. Cone Pulleys. It is often necessary to provide a range of speed variation in a shaft belted from a line shaft running at a constant rate. A familiar case of this kind is the ordinary lathe spindle. This may be done by shifting the belt from end to end of either a pair of cones or conoids, Fig. 106, depending on whether the belt is crossed or open. To work satisfactorily, a shipper must be located at each cone or conoid to guide the belt ; otherwise it may climb. As these ship- pers give trouble and wear the belt, and the belt itself is unequally stretched, it is usual to approximate the conoids by stepped cones, or cone pulleys. In order to have the belt equally tight for each pair of steps, the diameters of the steps must be so proportioned that the length of belt re- mains constant. It can be shown, geometrically, that for a crossed belt this condition is obtained when the sum of the diameters of each pair of steps is constant. In Fig. 106, a three-step cone with crossed belt is shown; and, adding together the diameters of the pair of steps connected by the belt, we have 11+6=17 for the constant of this cone pulley. For an open belt, an extended calculation is necessary for diameters giving a constant belt length, and a simple graphic method for laying out the cones has been published by Mr. C. A. Fig. 105. Belt Drive with Main Pulleys of Different Diameters . 126 MACHINE DRAWING Smith in "Transactions of the American Society of Mechanical Engineers" (Vol. 10, p. 269). Here the distance between shafts and diameters for one cone pulley is assumed, or is known from the conditions of the drive. In Fig. 107, lay off AB equal to the distance between centers of shafts; and with these points as centers, draw circles C and D equal, respectively, to the maximum and minimum diameters of the -o Fig. 106. Cone Pulleys for Spindle and Countershaft given cone pulleys. Draw the belt line EF. From a point G, half- way between A and B, erect GH perpendicular to AB, and make it equal to 0.314 AB (for the sake of space, it is not drawn to this scale in the cut) . With H as a center, draw a circle tangent to EF; then the belt line of any other pair of pulleys must be tangent to this latter circle. Assume B l the diameter of one of the pulleys, and draw a common tangent to circles D x and H, producing it past the center B< From B draw a perpendicular BF t to the common tangent; and with BF X as a radius, draw in the circle C v which will give MACHINE DRAWING 127 the pulley required to work with D v and having approximately the same length of belt as on pulleys D and C. Continue the process until the required number of steps have been obtained. It must be noted that the limit for which this construction can be used is reached when the belt angle K is equal to 18°. When the angle K is between 18° and 30°, proceed as follows: Locate another point J on the line GH so that the distance HJ is equal to .298^45; draw a tangent to circle H, making an angle of 18° with the line of cen- ters ABy and from point J draw an arc tangent to this tangent. Make all belt lines which are greater than 18° tangent to this arc. Belt Holes. Very often a belt has to pass through a floor or partition. The holes through which the belt runs should be large enough to be sure that the belt shall never strike the sides, but it is desirable that they should be ho larger than is nec- essary to accomplish that result. Accordingly, the holes should be laid out so that they may be cut in the right place and at the proper angle. Figs. 108 to 110 show the method of locating ., ... » , i n ii /. Fig. 107. Diagrammatic Layout for Cone Pulleys the position or the floor holes lor the various kinds of belts, the top only of the floor being shown. In Fig. 108 we have a common open belt. The circles repre- senting the pulleys are drawn, and the belt drawn around them. A short pitch line should be also drawn in each part of the belt where it passes through the floor. These parts of the pitch line are simply lines parallel to, and halfway between, the lines which repre- 128 MACHINE DRAWING sent the outer and inner faces of the belt. Next draw the two rectangles which represent the plan view of the pulleys, and draw through them the center line RS. From the points E and H, where the pitch line intersects the line representing the top of the floor, draw perpendiculars to RS, meeting it in points F and G. F and G are the center points of the rectangles 12 3 4 and 5 6 7 8, which form the outline of the belt holes on the surface of the floor. The long dimension of the rectangles will be parallel to the shafts on which the pulleys are located. After the belt holes are so found, the distances of their center lines to the right or left of the lines T and X, respectively (which are the center lines of the shafts), can be measured on the drawing, and the workman can mark them out on the floor by plumbing down (or up) from the shafts, getting the lines T and X on the floor di- rectly under or over the center of the shafts, and thus locating on the floor the points F and G, and conse- quently the belt holes, from the dimensions taken from the drawing. Fig. 109 shows how to draw the holes for a crossed belt. Draw the two views of the pulleys and the center lines AC and DB of the belt in the elevation; also the center line RS in the plan. It is well, also, to draw the belt complete in the elevation, as it makes it easier to determine which way the belt holes will slant. From points E and 11, where the center lines of the belt intersect the floor line, draw EL and HK perpendicular to RS, and meeting RS in F and G. The points F and G are the center points of the belt holes, and it only remains to determine the angles which the center lines of the holes make with T and X, respectively. These will be the same as the angles made with HK and EL. When the belt is leaving the pulley at A, a line drawn perpendicularly across to its inner face would occupy the position indicated by the dotted line aa! in plan; Fig. 108. Diagram Showing Method of Locating Belt Holes MACHINE DRAWING 129 and the belt, in passing from A to C, twists through an angle of 180°, and the line which was at aa f will occupy the position cc'. There- fore, when the belt has passed from A to H, it will have twisted Fig. 109. Diagram Showing Location of Holes for Crossed Belt through an angle which will bear the same relation to 180° that the distance AH bears to the distance AC. That is, if AH = l of AC, the angle JGK is \ of 180°, or 45°. Whether the angle JGK shall be laid off to the right or to the left of line H K, must be reasoned out by considering which way the belt twists in passing A to C. The angle of the other belt hole (LFM) is determined in the same way. 130 MACHINE DRAWING Fig. 110 shows the method of finding the belt holes of a plain quarter-twist belt, similar to Fig. 98. The centers G and F in plan are found by projecting from the elevation, as shown by the con- struction lines. The angle which the center line of hole at G makes with the center line of the shaft, is found by dividing 90° in the ratio of the distances P and N. The angle of the center line of the belt Fig. 110. Locating Belt Holes for Quarter-Twist Drive hole at F with the center line of the shaft, is found in a similar manner, by dividing 90° in the ratio of the distance AE to EC. It is usually sufficiently accurate, however, after having found the angle at G, to draw the center line of the other hole parallel to it. MACHINE DRAWING 131 General Practice. Working Conditions. A belt drive is work- ing under the most favorable conditions when, though not pulled up excessively, the belt "hugs" the pulleys tightly and wraps a large proportion of their circumference. Slipping. In the case of two pulleys of different diameters, made of the same material, connected by a belt, the belt will slip first on the smaller pulley, partly because the wrap of the belt is less upon that one, partly because the belt does not "hug" so tightly, owing to the smaller radius of curvature to which the belt must be bent. Sometimes the smaller pulley is lagged with rubber or leather so as to give it increased grip on the belt, thus making up for the tendency to slip, due to its small diameter. Location of Slack in Belt. On an inclined or horizontal drive the slack side should be on top, and the tight or pulling side under- neath, as the weight and slackness of the belt will act together to cause it to sag and increase the wrap. It is a well known fact that the greater the arc of conl^ct, the greater the driving force which may be obtained from the belt. Vertical Drives. Vertical drives should be avoided as much as possible, as here the weight of the belt is always tending to decrease the "hug" on the lower pulley. Diameters of Pulleys. Increasing the diameter of pulleys, the same linear speed of belt being maintained, does not increase the power transmitted, except by permitting the belt to "hug" the pul- leys more tightly; and the larger the pulleys, the better this condition becomes, providing we do not exceed a certain economic speed for the belt. Flexible link belting, made of small leather links joined together by steel wire, gives excellent results, especially when used on horizontal drives, but it is rather expensive to install. A pulley rim perforated with small holes, to prevent any air cushion beneath the belt, is another means of increasing the "hug." Belt Tighteners. Belt-adjusting devices are often provided for changing the distances between the pulleys, thus enabling the proper tightness to be always maintained. Motor and dynamo bases are provided with slides and set screws for such adjustment. A tightener pulley is often used to increase the wrap of the belt or maintain the proper tightness. This is an idler pulley, which is weighted, or adjusted by screws against the belt. While such a 132 MACHINE DRAWING pulley is a very ready and simple means of accomplishing the purpose, yet it should be remembered that the shaft carrying it is subjected to heavy pressure in its bearings, due to the belt tension; and the friction of the drive is considerably increased thereby. Tightener pulleys are used only when specific conditions prevent the results from being otherwise secured. Stiffness of Belt. It is generally preferable to use belts of two or more thicknesses for the sake of side stiffness, and also in order that any local imperfections of the leather in one layer may be taken care of by the other. Where the belts are to be shifted laterally, stiffness is an important item. If too pliable a belt is used on cone pulleys, the edges are apt to curl up, and the belt tends to climb and chafe against the side of the step, twisting like a corkscrew, and sometimes jumping from one step to another. Distance Between Pulley Centers. A good distance between the centers of shafting for ordinary belt drives is from 20 to 25 feet. With greater distances, the belt is apt to flop and run in waves; while at a less distance, the necessary tightness of the belt results in undue stretching. In crossed belts, the above distances should be especially adhered to; for, with a wide, stiff belt and a short distance between centers, there is an excessive amount of rubbing on the sides of the belt, as well as strain caused by the twisting. Crossing and Quarter- Twisting. It is well to use as few crossed and quarter-twist belts as conditions will permit. In quarter-twist belts, the side angle, where the belt leaves the pulley, should be kept under 25°, as considerable power is lost in side slipping. For the least distance between the shafts a safe value is obtained if the distance is made not less than 2J times the diameter of the larger pulley. A narrow belt gives better results than a wide one, on twisted belting. GEARS General Theory of Gears. Fig. Ill represents a pair of disks fastened to shafts A and B, respectively, and touching at the point P. If these disks be pressed tightly against each other, sufficient friction will be produced between them to cause one to drive the other. The number of revolutions B would make in a given time, would be to the number of revolutions made by A as A P is to BP ; or, Revolutions B _AP Revolutions A BP MACHINE DRAWING 133 Such friction disks will transmit but very little power without slip- ping; and even when required to transmit small power, cannot be depended upon to drive positively, as the least wear or loss of adjust- ment is liable to make them slip. Hence teeth are provided on each disk, such that they will lock to- gether and make it sure that when one disk is rotated the other must move also, without regard to whether the disks are pressed tightly F i g . in. Diagram of sh^iToear Prin- together or not. In fact, it is desir- Clp e able that this side pressure be avoided, in order to prevent excessive friction in the bearings of shafts A and B. Any shapes whatsoever of teeth would answer, provided they interlocked, so far as positive driving is concerned. But in order that the revolutions of the shafts shall always be inversely as the contact radii, or Revolutions B _AP Revolutions A BP it can be shown by geometry that the common normal drawn through the point of contact of any pair of teeth must always pass through the point P. A pair of gears, therefore, may be considered to be based on two disks, touching as in Fig. Ill, and provided with teeth such that these two conditions are fulfilled : 1. Positive driving at all times. 2. The common normal through the point of contact of any pair of teeth always passing through the pitch point. Pitch Circles. The circles corresponding to the disks are known as pitch circles, their diameters pitch diameters, and the point of contact P the pitch point (see Fig. 112). The distance, measured radially, from the pitch circle to the top of the tooth is called the addendum; and the circle through the top of the tooth, the adden- dum circle. The distance, measured radially, from the pitch circle to the beginning of the fillet at the bottom of the tooth, is called the dedendum; and the circle through this point the dedendum circle. In order that the top of the tooth on one gear shall not strike the surface between the bottoms of the teeth on the other, a further 134 MACHINE DRAWING distance is allowed between the dedendum circle and the root circle, known as the clearance. The distance from the center of one tooth to the center of the next, measured on the pitch circle, is called the circular pitch, and is evidently equal to the circumference of the pitch circle divided by the number of teeth. In order to run together, two gears must have the same circular pitch. The number of teeth in a pair of gears is proportional to the circumference of the pitch circles, and therefore to the pitch diameters, or pitch radii. The speeds of the shafts carrying the gears, being inversely proportional to the diameters of the pitch circles, are also inversely proportional to the numbers of teeth. / CENTER DISTANCE or "V r0< GEAR -B. DRIVEN Fig. 112. Layout for Pair of Gears, Showing Construction Features Circular and Diametral Pitches. Since the circular pitch is equal to the circumference of the pitch circle divided by the number of teeth, there is a fixed relation, for any given gear, between the pitch diameter and the number of teeth. This relation is known as diametral pitch. Diametral pitch is not a distance, like circular pitch, but is the number of teeth per inch of pitch diameter of the gear. For example, if the diameter of the pitch circle of a gear of 60 teeth were 20", the number of teeth per inch of diameter would be 60 9?; = 3, and the gear would be described as a "60-tooth, 3 diametral- MACHINE DRAWING 135 pitch gear". The product of the circular pitch times the diametral pitch, is always equal to the constant, 3.1416; that is, if we have one kind of pitch, and wish to change to the other, we divide 3.1416 by the given pitch. For example, 4 diametral pitch is equal to 3 1416 ~^-r — = .7854' / circular pitch. Again, 2" circular pitch is equal to 3 1416 —^ — - = 1.57 diametral pitch. Note carefully that diametral pitch is not "inches", but number of teeth per inch of diameter. Diametral pitch is very convenient to use, as the calculation is simpler than with circular pitch, and the pitch diameters of the gears come in even figures, or in even fractions of the pitch. For machine- cut gears it is universal practice to use diametral pitch in the speci- fication. For cast gears, w T here the teeth are fashioned by the pattern maker, it is common to use circular pitch. The thickness of the tooth LM, Fig. 112, is practically the same as the space TL for machine-cut gears. For cast teeth, however, the tooth must be thinner than the space, to allow for the inaccuracies of the pattern and casting. This allowance measured on the pitch circle is called backlash. Discussion of Terms. These terms are illustrated in Fig. 112; also the common normal KP to a pair of teeth in contact. Gear A, being the driver in the direction shown, a pair of teeth are in contact at point K. The curves of the teeth being of the correct shape, if a common tangent be drawn, and a perpendicular erected at the point of tangency K, it will pass through the pitch point P. Now, as the gears move in the direction of the arrows, the teeth slide upon each other, and the point of contact changes, coming closer and closer to point P, then passing through P, and, going on, reaches some point as J, which, in the present example, represents the second pair of teeth in contact. During all this motion of the teeth, the common normal at every point of contact will pass through the pitch point P, thus fulfilling the condition of uniform velocity. Pressure Line. It will be remembered that the pressure line between tw r o surfaces, as illustrated in the discussion of cams, is the common normal at the point of contact. Now, a pair of gear teeth is like a cam and its follower; and if we wish to find the direction of the pressure between them, we simply draw the common normal. 136 MACHINE DRAWING Hence, knowing that with the teeth of proper outline the common normal will pass through the pitch point, we merely find the point of contact of any pair of teeth and connect it by a straight line to the pitch point, thus giving the direction of pressure between the teeth at the given position. CYCLOIDAL GEARS Two kinds of curves fulfill the requirement for gear teeth, that the common normal shall pass through the pitch point. These are the cycloidal and involute curves * The latter curve, for many reasons, has almost entirely displaced the former. The cycloidal curve is useful in special cases, and is still adhered to by its few advocates, as having peculiar merit, even for standard work. The general and best standard practice, however, is unalterably committed to the involute sys- tem, and experience has shown the reasons therefor to be sound ones. Formation of Cycloidal Curves. The student can best approach the subject of the design of gear teeth through a study of the Fig. 113. Methods of Drawing Cycloidal Curves Cycloidal System, the principles being capable of clearer illustra- tion. Hence this system will be first presented. The method of drawing the cycloidal curves by the use of rolling circles is illustrated in Fig. 113. The accurate curve, having been developed, may be transferred by the tracing-cloth method, as in cams, to each individual tooth; or arcs may be found by trial which approximate to the true curve, or templets of stiff cardboard used. Design of Epicycloidal Gears. Fig. 114 shows a pair of epi- cycloidal gears designed to run together. The centers of the gears are at B and A; the pitch circles are shown in dot-and-dash, and are in contact at the pitch point P. The circle whose center is C, ♦Review the discussion of these curves in Mechanical Drawing, Part II. MACHINE DRAWING 137 shown dotted, by rolling on the inside of the pitch circle of the gear B, generates the hypocycloid PE, which forms the flanks of the teeth on gear B; and by rolling on the outside of pitch circle of gear A, generates the epicycloid PF, which forms the faces of the teeth on gear A. In like manner the circle whose center is D, by rolling on the inside of the pitch circle of gear A> generates the hypocycloid PG, which forms the flanks of the teeth on A ; and by rolling on the outside of the pitch circle of B, generates the epicycloid PH, which forms the faces of the teeth on B. The circles C and D are called the describing circles. If the gear B is the driver and is turning in Fig. 114. Construction of Ep'.cycloidal Gears the direction shown by the arrow, the flanks of its teeth act on the faces of the teeth on A from the point where they first come in contact until the point of contact reaches the pitch point; and from the pitch point on until the contact ceases, the faces of the teeth on B act on the flanks of the teeth on A. In other words, the hypo- cycloidal part of the tooth curve on one gear is generated by the same describing circle that generates the epicycloidal part of the tooth on the other gear with which it is in contact. This must always hold true, in order to have the gears run properly. The arc IP of the describing circle C, together with the arc JP of the describ- ing circle D, forms what is called the path of contact; that is, the point of contact between the teeth is always somewhere on the 138 MACHINE DRAWING line IP J. If the gear A were the driver, the direction of rotation remaining the same, the path of contact would be LPK. To design a pair of epicycloidal spur gears, we must have given the pitch (either diametral or circular), the diameters of the pitch circles, or the number of teeth, and something to determine the size of the describing circles. Manufacturers have found by experience what are the best ratios of describing circles to pitch circles, and gears are designed according to those ratios. It is not well to have the diameter of the describing circle greater than | the diameter of the pitch circle, and it is better to have it smaller. If a set of gears is to be made, any one of which is likely to run with any other one, the same size describing circle must be used for the faces and flanks of all the gears; and this describing circle is often taken | the diam- eter of the smallest gear of the set. Sometimes when two gears are not part of an interchangeable set, but are designed to run with each other only, the diameter for the describing circle for the flanks of each gear is made equal to the radius of that gear; and when this is the case, the flanks are radial straight lines; or, as it is usually stated, the gears have radial flanks. In Fig. 114, the two describing circles are of the same size and equal to the radius of the smaller gear, thus giving radial flanks on this gear. Let us proceed with the design of this pair of gears, given dimensions as follows: Gears to be 4 pitch (that is, as explained previously, 4 teeth per inch of pitch diameter); gear A to have 12 teeth; gear B 16 teeth; addendum equal to the diametral pitch; clearance equal to J the addendum; describing circles each equal to radius of gear A. Method of Drawing Gears. The steps in the process of drawing the gears are as follows : 1. Calculate the diameters of the pitch circles. 2. Draw the center line X Y on the paper; and on this center line locate the centers A and B a distance apart equal to \ the sum of the two pitch diameters. About these centers draw the pitch circles, of diameters as calculated. This will make the pitch circles tangent at the pitch point P. 3. Calculate the addendum and dedendum, adding this amount to and subtracting from the radii of the pitch circles. Then draw the addendum and dedendum circles with the radii thus found. MACHINE DRAWING 139 4. Draw the root circles with radii equal to the radii of the pitch circles minus an amount equal to the dedendum plus the clearance. 5. Draw the describing circles tangent to each other and to the pitch circles at the point P. 6. With the describing circle C rolling on the outside of the pitch circle of A, generate the epicycloid PF, continuing it until it meets the addendum circle of A. With the describing circle D rolling on the inside of the pitch circle of A, on the opposite side of line of centers from which the circle C rolled, generate the hypocy- cloid PG. Since the diameter of D is equal to the radius of the pitch circle of A, the hypocycloid PG will be a radial line; and conse- quently, after the student has become familiar with this fact, it will not be necessary actually to roll the circle to generate such a hypo- cycloid. The epicycloid PF and the hypocycloid PG together form one side of the tooth of gear A. 7. Divide the circumference of the pitch circle into as many equal parts as the gear has teeth, and through these points draw curves like the curve GPF. This may be done by making a templet of stiff paper that will just fit the curve GPF, and by means of this templet, transferring the curve to the points 1, 2, 3, etc. Next find the points a, b, d, etc., half-way between 1 and 2, 2 and 3, etc., since there is to be no backlash, and through these points draw curves similar to GPF, but turned so as to curve the other way. Now, by filling in with full lines that part of the addendum circle between the points F and N, R and S, etc., and filling in the root circle between T and V, etc., we have the outline of the teeth on the gear A. In practice, instead of making sharp corners at T and V, as shown by the dotted lines, fillets are put in with arcs of circles, these fillets being made as large as possible and still allowing space so that the corner of the teeth on the other gear shall not strike. 8. Construct the teeth on the gear B in the same way as the teeth on A were constructed, the describing circle D generating the epicycloid PH by rolling on the outside of the pitch circle of B, and the describing circle C generating the hypocycloid PE by rolling on the inside of the pitch circle of B. The hypocycloid is not a straight line in this case, as the diameter of C is not equal to the radius of the pitch circle of B. 140 MACHINE DRAWING The calculations for the above case are as follows: 4 pitch means 4 teeth per inch of diameter; and as there are 16 teeth in B, 1 A 19 its diameter will be -jv=4"; 12 teeth in A will give — = 3" diameter. The addendum for a standard machine-cut gear is usually made equal to the dedendum, and is equal to the reciprocal of the pitch. M-"' Fig. 115. Layout for Annular Gears Hence, to find the addendum and dedendum in the present case, take the reciprocal of 4, which is \ ". The clearance, being J the addendum, is equal to J- of \ = 3V" • If the student tries to follow the above description by actually drawing these gears, it will be found necessary to draw them to about 3 times their actual size in order to bring out the points clearly. That is to say, the pitch circles should be made 9" and 12"; the MACHINE DRAWING 141 addendum and dedendum f"; the clearance 3V; the numbers of teeth, of course, remaining 12 and 16. ANNULAR GEARS An annular gear is a ring with teeth on the inside of it. Fig. 115 shows such a gear, with center at A, meshing with its pinion. The Pig. 116. Construction for Epicycloidal Rack and Pinion method of drawing such a pair of gears is similar to that just de- scribed for two spur gears. Here the circle C, by rolling on the inside of the pitch circle of A, generates the faces of the teeth on A; and the circle D, by rolling on the outside of the pitch circle of A, generates 142 MACHINE DRAWING the flanks of the teeth on. A. The shape of the teeth of the pinion in the figure is found with the same describing circles placed at C and D' to avoid confusing the lines. In designing an annular gear and pinion, the diameter of the gear must never be so small that the distance from center A to center B shall be less than the sum of the radii of the two describing circles. If this should be the case, the teeth would interfere with each other. RACK AND PINION A rack is a gear whose pitch line is a straight line instead of a circle. Fig. 116 shows an epicycloidal rack in gear with a 16-tooth pinion. The describing circles are of the same size in the figure, although they might be of different sizes. The teeth on the pinion are drawn as described for Fig. 114, the construction lines for drawing them not being shown. The curves which form the faces and flanks of the rack are cycloids. The describing circle C, rolling on the pitch line of the rack, generates the cycloid PF, which forms the flanks of the rack teeth; and the describing circle D, rolling on the pitch line of the rack, generates the cycloid PH, which forms the faces of the rack teeth. The addendum and root lines are drawn parallel to the pitch line, and at a distance from it equal, respectively, to the distances A and R of the pinion. The teeth are spaced off on the pitch line of the rack by laying off the distances PK, KL, etc., equal to the circular pitch of the pinion. INVOLUTE GEARS Involute Compared with Cycloidal Gears. We have seen in the preceding pages how the outlines of cycloidal gear teeth are gener- ated by a point in a circle rolling on the pitch line. We have noted that the point of contact between the teeth is always somewhere on the describing circles, drawn tangent at the pitch point. The outlines of involute gear teeth, which are far more common than cycloidal teeth, are generated by a somewhat similar process. In the case of the involute, however, the describing point is located on a straight line, rolling, not on the pitch circle, but on another circle inside the pitch line, known as the base circle. The result of rolling a straight line, as noted above, is the same as if we stand up on the drawing board a small cylinder of diameter equal to the base circle, fasten one end of a string to some point in its circumference, and then MACHINE DRAWING 143 allow the string to unwrap from the cylinder, a pencil point at the free end of the string marking on the paper below it the involute curve. Design of Involute Gears. The method of drawing the involute curve is shown in Fig. 117; and it is obvious from this figure that the curve can never extend inside the base circle, although it may go any distance above it. Fig. 118 shows a pair of gears with involute teeth, drawn accord- ing to the principles stated below. The circular pitch and diameters of pitch circles are calculated in the same way as described for cycloidal gears. The centers A and B are chosen, and the pitch circles drawn tangent at the pitch point P, as before. In involute gears, the point of contact be- 8 tween the teeth is always some- where on an inclined line, CD, passing through the pitch point. The angle which this line makes with the tangent XY, is called the angle of obliquity (equal also to PBD). Its size has an im- portant bearing on the action of gear teeth; and there are special conditions which, for the best tooth action, would call for widely different angles. It is not well, however, tO have the angle Of Fi ^ 117 - Method of Drawing Involute Curves obliquity of different values, as it would then be impossible for any two gears to run together, except those based on the same angle. The angle of obliquity which has been quite generally adopted and which seems to fulfill the average conditions best, is 15°. In the present case, therefore, draw the line CD at an angle of 15° with the tangent XY; with A and B as centers, draw circles tangent to CD; these circles are called the base circles. The addendum, dedendum, and root circles are then drawn at the same relative distance from the pitch circles as in the case of cycloidal gears. The spacing of the teeth is now accomplished by stepping the dividers, set to the circular pitch, around the pitch circle. At any convenient points on the base circle, as G and E, generate the involutes in 144 MACHINE DRAWING accordance with the method of Fig. 117, or as explained in Mech- anical Drawing, Part II. Then, by the tracing-cloth method, or by the use of a templet fitted to this curve, draw in the tooth curves at points R, S, T, etc., on the pitch circles. This gives us the work- ing part of the teeth, and the remainder of the tooth to the root circle consists of a radial line. Fillets are put in at the bottom of the teeth, as in the case, of cycloidal gears. As has been stated above, the point of contact between the teeth is always somewhere on the line CD; it is therefore obvious that, if the circle struck through the top of the tooth on one gear cuts the base circle of the other gear at a point outside of point C, there can .err--— . - ~~"7PT|i ~ I" I *-..---,.. DRIVER I ,/ ■ DRIVEN » aSj Fig. 118. Diagram Showing Pair of Involute Gears in Mesh be no true contact at the top of the tooth. Instead of there being true contact, the top of the tooth will actually dig into the lower portion of the tooth of the other gear. This is known as inter- ference, and is overcome by slightly rounding off the top of the tooth down to the circle through point 0, so that it will clear. Since the path of the point of contact is along the line CD, this line also repre- sents the common normal to any pair of teeth in contact, and there- fore is the line of pressure between the teeth. The obliquity of this line of pressure to the line of centers AB causes a thrust between these centers, tending to force the gears apart; and this has been MACHINE DRAWING 145 considered an objection to the use of involute gears. With the standard 15° involute, however, experience has shown that this thrust is ordinarily of small importance. A similar thrust exists in cycloidal gears, but is constantly changing in value, being a maxi- mum at the beginning and end of contact of a pair of teeth, and zero when the pair of teeth are in contact at the pitch point. It will be noted that the involute tooth is of simpler outline than the cycloidal, being a single curve instead of a reverse curve. If the exact distance between the centers A and B of a pair of involute gears be not maintained, owing to wear or to some other cause, the gears w T ill still continue to run perfectly together; whereas in the case of cycloidal gears the action is seriously impaired by such a condition. BEVEL GEARS Bevel gears are used to connect shafts whose axes intersect. The angle between the shafts is not necessarily a right angle, but this is the most common angle used. Fig. 119 shows a pair of bevel gears connecting two shafts whose axes intersect at a right angle. The cones OP A and OPB are called pitch cones; the cones CPB and DP A, normal cones, and it is on these normal cones that the outlines of the teeth are laid out; BP and AP are the pitch diameters of the gears, and are found from the pitch and number of teeth just as the pitch diameters of spur gears are found. Design of Bevel Gears. To draw such a pair of gears, we must have given the angle between the shafts, the pitch and number of teeth in each gear, and the face of the tooth PE. The outlines of the teeth may be either involute or cycloidal ; the addendum, deden- dum, and clearance are determined by the same empirical rules as were applied to the other gears which have been discussed. Referring to Fig. 119, the gears shown are 2-pitch, 16 and 20 teeth, respectively, with face PE equal to 2 inches. According to previous understanding, the addendum or the dedendum for a standard tooth is the reciprocal of the diametral pitch — or, in this case, \" . Making the clearance \ of the addendum, would give \ of J" = tV'- The teeth are of the involute form, with an angle of obliquity of 15°. Choosing point 0, draw the lines OC and OB, making an angle of 90° with each other; calculate the pitch diameters of the gears; lay off on OC the distance OH, equal to \ 146 MACHINE DRAWING the pitch diameter of the smaller gear; and through // draw a line perpendicular to OC. In like manner lay off on OD the distance OJ, equal to J the pitch diameter of the larger gear; through J draw a line perpendicular to OD, meeting the perpendicular which is '^PITCH C/RCLE fig. 119. Construction Diagram for Pair of Bevel Gears drawn through H at P; and make HB equal to HP, and J A equal to J P. From A, P, and B, draw lines to 0, producing the pitch cones; through P draw CD perpendicular to OP, meeting OC and OD in C and D, respectively. Join CB and DA, and we have the normal cones. Through C, P, and D, draw perpendiculars. Draw MACHINE DRAWING 147 LMK parallel to CPD at any convenient distance. Draw arcs of circles tangent at the point M. These arcs are now to be treated as pitch circles on which to design the tooth curves, in exactly similar fashion to the method already outlined for spur gears. Through point M draw the line of obliquity SR, and draw the base circles tangent to this line. With the addendum chosen as above, equal to \" , it will be found that the addendum circle of the larger gear will cut the line of obliquity beyond the point R, where SR is tangent to the base circle of the pinion. This means that true contact cannot occur at the top of the gear tooth, so the tooth should be slightly rounded off, to prevent interference with the flank of the pinion. The limit of this rounding-off of the point of Fig. 120. Skeleton Diagram for Bevel Gears not at Right Angles the tooth is determined by striking a circle with center L through the point R, as it is obvious that below this point on the tooth of the gear there will be true involute contact. The root circles are drawn by setting off the clearance, as in the preceding cases. One tooth on each gear is drawn on the development of the pitch circle, and the completion of the drawing of the teeth in the several views of the gears is merely a problem in projection. With L as a center, draw a series of arcs (shown dotted) cutting the tooth which was drawn on the pitch circle, and the line LMK, at 2, 3, 4, etc.; from 2, 3, 4, etc., draw lines perpendicular to CD, cutting CD at 5, 6, 7, etc. ; from these points draw lines to 0; along P0 lay off PE; through E draw a line perpendicular to PO, cutting 148 MACHINE DRAWING 50, GO, etc.; and from the points of intersection draw other lines parallel to PB. With center 0' , taken at any convenient place on CO prolonged, and with radii equal in turn to a5, b6, etc., draw circles as shown. On the circle which is drawn with HP as a radius (marked "pitch circle"), space off the circular pitch; and on each of the circles in turn, lay off the teeth of the same width as they are on the corresponding circles drawn through 1,2,3, J+, etc. The rest of the construction can be understood by a careful study of the figure. The other gear is drawn in the same way. Intersecting Angles Other than 90°. The drawing of the teeth for bevel gears whose shafts intersect at another angle than a right angle, is accomplished by following out the same principles as noted in the case at hand. The skeleton outline of such a pair of gears is shown in Fig. 120, the angle between the axes being 60°. These gears are 2-pitch, 16 and 20 teeth, respectively, the same as in the previous case; and their construction affords an interesting comparison therewith. General Manufacturing Practice. To draw the teeth on a pair of bevel gears as described in Fig. 119, is a tedious process and requires considerable patience and drafting skill. It is really little more than an exercise in advanced projection drawing, but, as such, is valuable to the student. It must not be thought, however, that to detail a pair of bevel gears for manufacture, such a drawing is necessary. Usually, standard proportions of teeth are specified, and the detail of the gears is comparatively simple. An illustration of a pair of bevel gears of standard proportions of teeth, detailed ready for the workman's use, is shown in Fig. 39, Machine Drawing, Part I, and it is seldom necessary to show more. General Remarks on Gear Teeth. The foregoing study of the outlines of gear teeth is given in brief and elementary form. The student cannot hope to gain a familiar comprehension of the action going on between the teeth of gears, without going more deeply into the subject than is possible in these pages. The action of gear teeth is one of the most complicated subjects to investigate and under- stand, as with each new condition of number and type of teeth, new points of action are developed. A good practical article on gear teeth is "A Treatise on Gear Wheels" by George B. Grant; and the student is referred to this book for a further study of the subject. MACHINE DRAWING 149 There are many special points to be observed in designing the outlines of gear teeth, in order to insure the best operation of the gears. These points cannot be well explained without the actual undertaking of the design of the teeth. If the student wishes to familiarize himself with tooth action, he cannot do better than to choose a variety of cases, and lay out each one, studying the several points as they come up. It should be remembered that the action of a small pinion, meshing into a large gear is considerably different from that of two large gears meshing into each other. With certain relative numbers of teeth of gear and pinion, as many as three pair of teeth may be in contact at all times; while, in certain other combinations, but two are in contact at all times, and in certain others only one. Changes in the tooth dimensions, diameters of describing circles, angles of obliquity, etc., alter all these conditions, so that there is an endless variety of combinations, each of which presents some new feature only to be understood by actual layout of the particular case. In gear-tooth work, the student will often find it an advantage to make the layouts to double the actual size, and sometimes larger. A fine, hard pencil must be used, and extreme accuracy in deter- mining the points must be adhered to. The layout of gear teeth is one of the severest tests of the draftsman's ability in line work.^ PLATES Plates V to X, inclusive, are to be drawn by the student for practice in applying the principles of screws, springs, cams, belts, and gears. These plates are to be made the same size as those of the preceding Instruction Papers of the course; viz, 11" by 15", outside, with a margin of J", making the clear space for the drawing 10" by 14". PLATE V Fig. 1. Make a theoretical drawing of a right-hand, single, sharp V thread screw, 4" in diameter, 6" long, 1" pitch. Construct the true helix as shown in Fig. 62 of the Instruction Paper. Show dotted construction lines for one complete turn of the helix. Fig. 2. Make a conventional representation of a single right- hand, square-thread screw, 2" in diameter, 3V long, \" pitch (2 threads per inch). 150 MACHINE DRAWING Fig. 3. Make a conventional representation of a single, right- hand, U. S. standard V thread screw, 2" in diameter, 3J" long, 4| threads per inch. Use form shown in Fig. 74. Fig. 4- Make a conventional representation of a single, right- hand, sharp V thread screw, 1" in diameter, 3f " long, 8 threads per inch. Use form shown in Fig. 73. Fig. 5. Same as preceding figure except make left-hand, and' double thread. Fig. 6. Draw a right-hand helical spring, j% -inch round wire, inside diameter of spring If", length 3|", pitch §", using form shown in Fig. 58. All the figures on this plate are to be made and inked in on the drawing paper. PLATE VI Fig. 1. Draw a plate cam, the top turning to the right, to raise a slide (having a roll at its lower end) 1|" with harmonic motion, while the cam turns through 135°, then to allow a fall with uniform motion while the cam turns through 180°, and rest for the remaining 45°. Make the center line of motion of the slide pass through the axis of the cam, the roll 1" in diameter, and at its lowest position \y above the axis of the cam. Show one view only, and do not show the shaft or hub of the cam, these being merely explanatory on the plate as shown. Use a hard pencil, with a fine point, and show pressure lines. Fig. 2. Draw a plate cam, the top turning to the left, to raise a roll, similar to that of the preceding figure, 1 \" with uniform motion, while the cam turns through 150°, then to rest for 30°, then to fall for the remaining 180° with a uniformly accelerated and retarded motion. Make the center line of motion 1" to the right of the axis of the cam, and at its lowest position the center of the roll 1J" (meas- ured radially) from the center of the cam. Show pressure lines. As inking will impair the accuracy of both of the figures on this plate, it should be handed in just as the pencil work leaves it. Special care must be taken to have the lines fine, sharp, accurate, and clear. Accuracy is of first importance in this case, and though the plate should be cleaned up as much as possible without destroying the con- struction lines, yet it cannot be expected that the plate will be as clean MACHINE DRAWING 151 when finished as though it were inked, thus giving opportunity to rub over the whole drawing. PLATE VII This shows plan and one elevation of two pulleys located on two shafts at right angles to each other. Draw these two views and another elevation, showing the belt on the pulleys in all three views, and place arrows to show the direction of motion of the pulleys in order that the belt may stay on. The dimensions are given in feet and inches, but the drawing cannot be made full size. As stated in the title, the scale may be 1" per foot, that is, the distance between the shafts being 8', it is made on the drawing 8". Other dimensions are to be reduced in the same proportion, or to one-twelfth size. This plate should be inked in on the drawing paper. PLATE VIII Fig. 1. With center 3" from the extreme left of the sheet, and on a horizontal line through its middle, strike the arc of a pitch circle with 6" radius. Take describing circles of 4" diameter, and roll them upon both sides of this pitch circle, producing at least three epicycloidal teeth, diametral pitch 1J, addendum §", dedendum §", clearance J", thickness of tooth equal to one-half the circular pitch. Note that the diametral pitch, \\ as given, is not "inches", but num- ber of teeth per inch of diameter of pitch circle. In order to lay out the teeth, the circular pitch must be calculated as explained in the Instruction Paper. Fig. 2. W T ith center 5 J" from the extreme right of the sheet, and on the same horizontal line as before, strike the arc of a pitch circle with 6" radius. Take angle of obliquity equal to 15°, and draw the base circle for involute teeth. Draw at least three full involute teeth, diametral pitch 1J, addendum § ", dedendum §", clearance J", thickness of tooth equal to one-half the circular pitch. As before, the circular pitch must be calculated, and when' the teeth are finished it should be noted how different is the shape of the involute tooth from the epicycloidal, yet both are correct working teeth for the same diameter of pitch circle. Both figures of this plate should be handed in just as the pencil work leaves it, for the same reasons as for Plate VI. 152 MACHINE DRAWING PLATE IX Draw a horizontal line through the middle of the sheet, and, choosing a center 1" from the left-hand side of the sheet for the pinion, draw an 18-tooth pinion meshing with a 30-tooth gear of the involute, spur-gear type. Make teeth 2 diametral pitch, angle of obliquity 20°, addendum J", dedendum J", clearance T V', thickness of tooth one-half the circular pitch. Draw as many teeth as there is room for across the plate, show the length of the path of contact, and state the greatest number of teeth which can be in action at any one time. This plate should be inked in with as fine lines as possible, in order not to greatly impair the accuracy of the work. PLATE X Draw a horizontal line 5f" from the bottom of the sheet and a vertical line 4" from the left-hand side as axes for a 27-tooth bevel gear and a 16-tooth pinion respectively. Make the teeth 4 diametral pitch, addendum \", dedendum J", clearance ¥ V, length of face 1J". Make an outline like Fig. 120, indicating the pitch diameters, pitch cones, and normal cones. This plate should be inked in, fine lines being used for the con- struction lines, and heavy ones for the body of the gears, which may be made any proportions to suit the student's conception of what they should be. This may be treated as a case for development of the student's mechanical judgment and sense of proportion, based, of course, on the exact skeleton outline made from the data as given. EXAMINATION PLATES Drawing Plates V to X, inclusive, constitute the Examination for this Instruction Paper. The student should draw these plates and send them to the School for correction and criticism. Reproduced plates of Nos. VIII, IX, and X, are not sent to the student; he should work out the problems for himself, following the directions given. The date, student's name and address, and the plate number, should be lettered on each plate in inclined Gothic capitals. 0. _i < r O CO 1= § CO CO g c UJ z or < RING > CONV SENTA O CO CO < £ , LJ o 3 UJ i I i / / / L L_ _J Uie- PLA TE HI QUARTER- TURN BELT SCALE I"-!' TOP OF FLOOR SEP'T /4J9/3 HERBERT CHANDLER, CHICAGO, ILL. 0- >« « W O ►J On \ MACHINE DRAWING PART III A— MECHANICAL WORKING SHOP DRAWINGS In Mechanical Drawing, Parts I to III, inclusive, the funda- mental principles were explained and illustrated. In Machine Drawing, Parts I and II, the production of working drawings has also been discussed to some extent, and the usual characters and symbols explained and applied. The elementary work already out- lined has been treated chiefly from the standpoint of correctness of line representation considered by itself, without a detailed study of the use to which the drawings so produced are to be applied. Evidently this is the proper method, for the student should gain a thorough understanding of the principles which underlie line representation before attempting to apply them to any extended practical use. In all of this preceding work it was intended that the theoretical principles should overshadow any incidental refer- ences made to practical application, however true and pertinent the latter may have been for purposes of illustration. Hence, before taking up any advanced work, the student should fully realize the importance, in fact, the absolute necessity, of thoroughly under- standing the fundamental principles which have been outlined in the preceding books. At this point the student must realize that a lack of proper elementary and fundamental training will make him "go lame" at every point of his course, and probably prevent the attainment of proficiency which otherwise would naturally and almost instinc- tively come with advanced study. It is thorough and ready knowl- edge, always at his fingers' ends, of all the principles of Mechanical Drawing, which makes the expert draftsman. Plan and Scope of Advanced Work. Utility the Guide. It is now intended to throw an entirely different light on the matter, and 158 MACHINE DRAWING view the subject of Machine Drawing from a purely practical stand- point, that of utility. It is assumed that the student understands and can use the principles which have been previously discussed. If in a working shop drawing we choose to modify any of these theoretical principles, it will be because of increased value in the utility of the drawing. For example, we may desire to omit some portions of an elevation or plan or side view of a complicated cast- ing, because certain details will thus be more clearly brought out. We may make a "zigzag" section to show construction which,- by absolute fidelity to theoretical principle, would be confused, or hid- den in a maze of dotted lines. We may find it convenient to place in some unoccupied corner of a drawing a layout which could not be in the least justified by any rule of projection. • A multitude of transgressions like these occur on good drawings, and they are certainly justifiable from the standpoint of utility, which is the true ultimate end sought for in a practical shop drawing. These variations from the theoretical are not strictly conven- tionalities, because they are not classified or established, so far as we know, but are the spontaneous outgrowth, as the occasion de- mands, of the draftsman's purpose to make his drawing one of greatest utility. He can, however, safely transgress a principle only when he thoroughly knows the principle; otherwise a blind deviation from the theoretical path will inevitably lead to difficulty. All of the above is intended to impress the student with the idea that theoretical principles are his best, in fact, his only tools to work with; but they are not "self-hardening," like "mushet" steel; they are like the finest grade of tool steel, which must be tempered and ground and used with the best judgment of the oper- ator, to secure the most satisfactory results. Student Drawings. A student's early drawings are usually unsatisfactory, even to himself. Somehow they do not look like those seen in shops, and as a rule he is unable to see why this is so. Of course the difference is to some extent due to the experi- ence of the professional draftsman. However, the superior results of the latter's work are attained largely through his systematic and workmanlike habits of execution. It should encourage the student in his early attempts to know that these essentials to the infusion of life and shop spirit into a drawing can be analyzed, out- MACHINE DRAWING 159 lined, and grasped at the outset by earnest, intelligent effort, and really good workmanlike results obtained. To discuss and, if possi- ble, to impart these essentials of a working shop drawing to the student, is the purpose of the present book. Essential Requirements. The two chief essentials of a shop drawing, under which general heads a multitude of detail require- ments can be summed up, are : (1) Absolutely complete and definite instructions from de- signer to workman. (2) Least possible cost in dollars and cents of production of the drawing measured by the draftsman's time. It makes no difference how much we may attempt to disguise these two elements, the fact will still be apparent that "complete instructions furnished for the least money" is what the manufac- turing shop is after,. and what will be assumed as a basis for judg- ment as to highest commercial utility. Completeness of Drawings. As to the first point, that of com- pleteness and definiteness of instruction, there must be no question of degree. If the information which the drawing furnishes is posi- tive and complete, the drawing is good. If doubt arises in the workman's mind as to what the designer intended by a certain line or' dimension, or if the dimension be omitted, the drawing is bad. There is no middle ground. The instructions are either present or absent, and the drawing good or bad accordingly. The workman of today is not permitted to assume dimensions or shape. It is his business to execute the draftsman's orders; it is, however, often his privilege to choose his own way of doing it, but further than this modern practice does not allow him to go. He is held as rigidly to the orders specified by the drawing as the loco- motive engineer is held to his bit of tissue telegraphic order to pro- ceed, without which he dare not enter the next block. The drawing is supreme; it is official; it must be plain, direct, and all-sufficient. It is the draftsman's business to make it thus, and he is not a drafts- man until he does. This idea uf positiveness must be thoroughly absorbed by the student. Positive action must be a habit which controls his every move, % which marks every dimension he prints, which directs every line he draws. Every line must mean something, must have a 160 MACHINE DRAWING definite reason for existence, must be necessary to illustrate the idea which he wishes to convey to the workman, and every line must be a definite measurable distance from every other line, so that its location is fixed beyond a doubt. Lines which mean nothing, and cannot be measured, have no place on the drawing; they only confuse it. A good picture of a machine could scarcely be called to the same service as a good drawing of it. The picture might give us an excellent idea of the machine, but for the purpose of the actual construction the picture is useless, while the drawing is of positive value. This value exists simply because of, and in proportion to, the completeness of detail which it shows. Hence in making a shop drawing the picture idea is entirely subordinate to the idea of utility, the latter, in fact, being the measure of its value. There are certain classes of drawings — of which the Patent Office drawing is a good example — in the making of which the picture idea is predominant. Here the purpose is to illustrate mechanisms, not construct them; hence the function of the drawing is in no wise that of the working shop drawing, and as such does not fall within our discussion. Cost of Producing Drawings. The second general element involved in producing shop drawings is their cost, as measured by the draftsman's time. It is somewhat subordinate to the first element, for the drawing must be a good one, judged by an absolute standard, whatever the time or cost necessary to produce it. Cost, however, is an important item, and cannot well be overlooked. It is inevitable that in any enterprise economy will ultimately be sought, whatever extravagance an imperative original demand may have permitted. This is as true in the production of drawings as in the case of manufactured articles of trade. Drafting-room labor is a relatively high-priced service, and the salary list easily assumes considerable proportions, so that wasteful excesses count up rapidly. One of the qualifications of proficiency invariably required for this department of shop organization is rapidity of execution. This is not as dependent upon personal traits as at first might be supposed. A man may so husband his time and direct his efforts that he will easily distance his neighbor of more rapid motion. The latter may have less ability to make his energies count, and lack of judgment MACHINE DRAWING 161 as to when just enough, and no more than enough, energy has been expended on his drawings. From the standpoint of utility, the function of a drawing is fulfilled when it has reached the stage that it completely instructs; more time spent in elaboration is wasted, and is an unnecessary and therefore extravagant expenditure. The student must fully realize this. In his earnestness to produce fin- ished and complete work he must constantly strive to accomplish results in the least possible time. This does not mean careless haste; far from it. A complete shop drawing cannot be made by short cuts, but through a systematic building of line on line, dimen- sion on dimension. This is in sharp contrast to a haphazard habit of developing a drawing, first a line here and then a figure there, with no definite purpose in mind, and no hint as to when the drawing is actually completed. The one method constitutes the efficient draftsman who works easily, receives a high salary, and is worth it, because he wastes no time in unnecessary labor. The other marks his unfortunate brother, plodding laboriously far behind, receiving a small pittance per hour, and worth less, because he does uncalled-for labor, and loses his definiteness of purpose in a maze of unexplainable lines and figures. A working shop drawing, commercially considered, may well be defined as being "Complete instruction from designer to workman issued at minimum expense." This definition should be memorized by the student, and con- stantly kept in mind while making a drawing. The preceding pages should be re-read with this in view until the full spirit is appreciated. The maxim as given above, if faithfully adhered to without modification, answers nearly every question that can be raised as to the excellence of a drawing. It can be used as a standard of judgment, whatever system of lines or symbols may be in vogue. It permits a draftsman to adjust himself to the rules of any shop or drawing room, and yet produce a good drawing and satisfy his employer. A drawing which is cheaply produced yet at the same time does perfectly that for which it was made, viz, conveys complete instruction, is beyond commercial criticism. 162 MACHINE DRAWING Method of Procedure. As the general objects to be attained in a working shop drawing have now been presented, it is necessary to indicate in detail how the work may be properly accomplished. In order to do this, it is proposed to produce systematically a full set of working drawings of a familiar and comparatively simple machine. The methods used will be those of a designing detail draftsman, producing commercial work fit for shop use. In the progress of the work, from its beginning in the rough, though accur- ate, pencil layout, to the completion of the tracings and the order sheets, the same bold style, clearness, directness, and businesslike spirit which the shop atmosphere and surroundings would naturally supply will be emphasized, and so far as possible imparted to the student. It is expected that the student will follow the text closely and study the plates carefully, endeavoring to familiarize himself with every detail illustrated. The more closely he is able to apply himself in this respect the better will he be able to partake of the life and spirit which is intended to be conveyed, and without which the true character of the work can be but poorly developed. Incidentally, several purposes will be fulfilled by this treatment. Practice in Reading Drawings. Ability to read drawings quickly and intelligently is almost as important as making them, and it is expected that the study of the plates, with a view to thor- oughly understanding every line, will develop proficiency in the art of reading drawings. Discussion of Tools and Machine Parts. The discussion in the text of not only the form of the machine parts themselves, but also the tools and shop processes to produce them, affords considerable insight into the influences affecting good machine design. Without introducing any mathematical analysis or investigation, which is beyond the province of this book, much practical consideration as to the restrictions imposed by existing shop methods upon theoretical construction will be suggested, and the student encouraged to use his judgment thereon. Imitation of Pencil Sketches. In the preliminary layouts the actual "sketchy" appearance of the pencil drawing will be imitated as far as possible, so that the student himself may imitate and catch the bold dash, yet fine accuracy, of the linework, which is characteristic of the expert draftsman. MACHINE DRAWING 163 Making of Complete Bra icings. The completeness of a set of drawings is as important a lesson as the completeness of each draw- ing itself. In this is involved the proper arrangement and classi- fication of details, the foundation layout, and the system of order sheets for getting work into and through the shops. This is a feature which very strongly affects some of the finishing touches to a drawing, for it is so easy to omit a "few last things" and turn in an uncompleted sheet. Every draftsman knows how many little things come up toward the close of a job involving complete draw- ings of a machine, and how strong the tendency is to omit them, and relieve himself of somewhat tedious details. The result is irritation and delay when the drawings get into the shop, and they return to the drawing room to be fixed up at a time probably incon- venient for all parties concerned. A good draftsman will turn in a complete set of complete drawings. It is highly important that the student grasp this idea, and study his work accordingly. DUPLEX PUMP PLATES Reasons for Choice of Pump Specifications. The typical set of plates chosen for this book in fulfillment of the above purposes, takes up the study of a simple, duplex steam pump. This particular type of machine represents the simplest and most elementary form of the steam engine in modern use in respect to valve gear and con- trolling devices. It is not an economical machine, yet its principles lie at the foundation of the economical high-speed engine, the latter being produced through a modification of the uneconomical valve gear such as is found on a pump of the type chosen, rather than through any radical change of construction as to the body of the machine. Hence the study of a steam pump may well precede that of higher forms of the steam engine. It is hoped that the study will so interest the student that he will be led to further investigation and development not only of the steam engine itself, but of that highly important division of modern engineering — pumping machinery. Thus we note another point of advantage in the study as out- lined. The power end of the machine introduces us to the steam engine; the load end is the beginning of the engineering of pump- ing machinery. 0- > 3 o u- _J u X o r. -j _J u 0- z. o 3 r o- o P o MACHINE DRAWING 165 Rating of Pump. A steam pump is rated by the bore of its cylinders and length of stroke, all being given in inches. A "16X8|X12 pump" means that the steam cylinder is 16 inches in diameter, the water plunger 8| inches in diameter, and the nom- inal length of stroke 12 inches. These sizes are always given in the same order, beginning with the diameter of the smallest cylinder (in case there is more than one), then the diameter of water plunger, the common stroke of both being placed last. This expresses to the mechanic the rating of the pump in the clearest style and briefest language. The pump illustrated here is designed for standard service, operating under a steam pressure not to exceed 100 pounds per square inch, water pressure not to exceed 150 pounds per square inch, and the rated capacity based on an average piston speed of 100 feet per minute being about 550 gallons. This requires that each side of the pump shall handle 275 gallons and, being double acting, shall make 100 reversals or 50 double strokes per minute. PLATE A. STEAM END LAYOUT This plate illustrates, as nearly as reproduction can accomplish, the pencil layout of the steam end. It is the first work of the design- ing draftsman. The drawing as shown is exactly the type of layout which he would turn over to a detail draftsman, whose duty it would be to work up detail shop drawings therefrom. Characteristics of a Layout. The character of this drawing should be carefully studied. Remember that it is a layout, nothing more; also bear in mind that it is an exact, measurable working sketch. Attention is called to the sharpness of the lines, especially to the clean-cut intersections. Note the boldness, dash, and business- like style, the freehand cross-section lines roughly put in. There is no hesitation or worry as to where the end of a line shall be, or whether it crosses other lines which it theoretically should not. The intersections are allowed to indicate the termination of lines, and the rough section lines pick out the parts and separate them clearly to the eye. There is, in this layout, the spirit of confident, definite, and rapid action, with no thought for absolute finish in linework, but with every thought for absolute results as to measur- able dimensions. 166 MACHINE DRAWING Relations of Different Drawings. The data for the production of Plate A by the student are rather more complete than he would usually find in practice. Plates B, C, and D show many details fully. The steam cylinder and head, however, as shown in Plate B, are not dimensioned, and the student's problem is to produce this plate complete, with finish marks, dimensions, and necessary data for a working drawing. In order to do this it is first necessary to work up Plate A with exactness, in pencil, and see that all parts go together properly. Then the detail of cylinder and head may be made separately by measurement of the layout drawing, and Plate B produced. For this work the ordinary brown detail paper is very satis- factory. A hard lead pencil is necessary, as hard as 6H, and the point must be kept well sharpened. Rules of Action. There are two general rules of action an pro- ducing a drawing which give the answer to the question which fre- quently confronts the beginner: "What is to be done first?" or "What is to be done next?" These rules are : (1) Draw everything that is positively known; and (2) work from the inside to the outside. Every problem has some positive data, assumed or calculated, to start with. The first thing to do in every case is to get this data represented by lines on the paper. An expert designer has been heard to say that until he had spoiled the blankness of his sheet of paper by some lines, he could not design. There is some- thing in this; and almost invariably the first line to draw is a hori- zontal center line somewhere near the middle of the sheet; draw it! Draw it at once without hesitation, and the layout is begun. We now have something about which to build. Development of Layout — In this case the designer would first calculate the size of the piston rod, and determine the fastening to the piston. He would then draw the rod and build a hub around it. He would next calculate the width or thickness of piston and size of packing rings, and draw the two vertical lines 5 inches apart, to indi- cate the piston faces. These lines would be limited by the cylinder bore, which he knows to be 16 inches; hence horizontal lines 16 inches apart, parallel to and symmetrical with the center line, are the next to be drawn. Short vertical lines indicate the location of MACHINE DRAWING 167 the packing rings. As the nominal travel of the piston is to be 12 inches, the location of the piston and rings can be shown on both sides of the central vertical line at the limits of travel. A clearance must exist between the heads and the piston (in this case J inch is allowed), hence the lines of the heads can be drawn, and the general inside outline of the cylinder barrel is complete. This is all in direct application of the foregoing rules, and is so simple, natural, and direct that it hardly requires such explicit statement. We have simply taken such data as we had and put it on paper, placing it where it can be seen from all sides, and where the mind is relieved of the labor of carrying it. If the student will only appreciate this one rule and draw all he knows about the problem, he is well on his way to its solution. Draw everything you know, and icork for ichat you don't know is what these two rules say, and the first question to arise should be: "Have I drawn everything that is known about the problem?" before he asks himself or any one else: "What shall I do next?" Dimensions in Even Figures. One other rule might be added to these two: Keep dimensions in even figures, if possible. This means that small fractions should be avoided. It is just as easy to bear this point in mind, and save the workman much annoyance and chance of error, as it is to disregard this matter. Even figures constitute one of the trade-marks of an expert draftsman. Of course a few small fractions, and sometimes decimals, will be necessary. Remember, however, that fractions must in every case be according to the common scale; that is, in sixteenths, thirty-seconds, sixty- fourths, etc. ; never in thirds, fifths, sevenths, or such as do not occur on the common machinist's scale. A systematic, definite mode of treatment on these lines must become a habit, so that all problems, however complicated, can be approached with confidence in the same way. It is the drawing of one line which makes clear the drawing of the next and subsequent lines ; and the most serious obstacle which the student is likely to set for himself is trying to see the whole problem through from the beginning. Even an expert cannot do this, but allows the layout to develop results as he proceeds. Cylinder Details. The details of the piston and rod being given in Plate C, the foregoing work is very easy for the student. The 168 MACHINE DRAWING thickness of the barrel and heads being determined (J inch in this case), the exterior outline may be partially drawn. The fixed head at the yoke end must be thicker than this, in order to receive the yoke and stuffing-box bolts without breaking through. The recesses or counterbores at either end of the cylinder should be so located that the packing rings run over the edge a little at the end of the stroke, thus preventing the wearing of a shoulder by the piston stopping in the same place every time. The counterbore should be deep enough to allow reboring the cylinder without the counter- bore being touched by the tool. In this way the counterbore is retained to center the cylinder at its original location. Port Details. The size of steam ports having been calculated, they may be drawn in, the turns being made easy and as direct as possible. The height to valve seat must be kept at the lowest limit consistent with sufficient metal between and outside of the ports. As the detail of the ports might be somewhat troublesome, it is shown in an enlarged sketch for the student's benefit, Fig. 121. Chipping or filing strips | inch high are left on the port edges, which must be true, in order to finish them up easily. The three inner ports are for exhaust, the outer ones for admis- sion of steam. This five-ported cylinder is peculiar to the direct acting steam pump, it being a device to effect the cushioning of the piston at the end of the stroke, thus preventing the piston from striking the heads. This is necessary, since no positive limit of motion exists, as is the case in machines with crank and connecting rod. When the edge of the piston has passed the outer edge of the exhaust port, as shown in Fig. 121, the steam, which has been ex- hausting through port A, is confined in space B and port C, and, being compressed by the piston, acts like a spring to retard its motion. If the point P is properly determined for a given speed, the piston will always compress the steam just enough to cause it Fig. 121. Enlarged Details of Steam Port MACHINE DRAWING 169 to stop at the end of the nominal stroke; in this case, \ inch from the head. It is evident, however, that at different speeds the piston will have more or less power to compress the steam, and will not stop at the point desired. This causes the trouble of "short stroke," and consequent inability to make the pump work to its full capacity. Now if we connect ports A and C by a small opening shown dotted at D, and control this opening by a plug valve operated by hand from the outside, we can let a little steam leak by into port A, thus reducing the cushion and allowing full stroke. In order to avoid complicating the drawing, no cushion valves are shown or required to be put on by the student. They are not customary in small pumps, but might advantageously be put on the present illustration. The valve seat must be a scraped surface, while the chest face need not be; hence the latter is finished § inch lower. This also gives a ledge against which the steam chest fits, thus securing posi- tive location. Cylinder Heads and Steam Chest. The bolting of the heads and the steam chest should allow a width of packing inside of the bolts of | to f inch, otherwise there is danger of the steam blowing out the packing and causing leakage around the bolts. The bolts do not fill the holes, the latter being drilled large, from rg to J inch. The spacing, if wider than 5 or 6 inches, is likely to permit springing of the flanges between the bolts, and consequent leakage. Bolts less than f-inch diameter are not desirable, as they can be easily twisted off with an ordinary wrench. In this case the cylinder head takes 8 _mcn bolts, the yoke, stuffing-box, and gland, f-inch. The flanges of heads and cylinders are usually from 25 per cent to 50 per cent thicker than the body of the casting. Drips, J-inch pipe tap, to be fitted with cocks, are necessary at both ends of the cylinder to readily drain the cylinder of water. Molding Steam Cylinder. The design is often influenced by the way in which the piece is to be cast. It often takes but a slight change of design to save many dollars in pattern making and foun- dry work. Hence the habit should be formed of always judging the design of a piece from the foundry standpoint. In this case it is evident that the ports and cylinder bore must be cored out, and the most obvious position of molding is to lay the cylinder on its 170 MACHINE DRAWING side, the parting line of the flask being along a vertical plane running lengthwise through the middle of the cylinder. This permits the chest flanges to draw nicely, likewise the ribs on the foot, and allows the thin curving port cores to stand edgewise in the mold. Another method of molding would be with the valve seat down. This would involve loose pieces for the chest flanges, and setting of cores for the cylinder foot. It would, however, assure sound metal beyond question at the valve seat. Spongy metal at the important wearing surfaces, the valve seat and cylinder bore, is not permissible in any case, and care in molding and good design are necessary for good results. All corners must be carefully filleted, and chunks of metal must be avoided, especially where several w T alls or ribs join. The metal must be kept of average uniform thickness, so that the whole casting will cool uniformly. Machining Steam Cylinder. The boring may be done on a vertical boring mill, the heavy arm carrying the tool being thrust down unsupported into the cylinder, the latter being rotated by the table to which it is clamped. If the horizontal boring machine is used, the hole through the inside head for the stuffing box must be large enough to permit a stiff boring bar to be passed through. This allows a support at each end of the bar, to take the strain of the cut. The plane surfaces may be finished on a reciprocating planer or a rotary planer. In the latter case it is desirable to keep all lugs or projections back from finished surfaces, in order to permit the large round head which carries the cutters to pass over them without interference. The drilling of standard machine parts of this character is usually done through jigs, or plates carrying hardened steel bush- ings laid out to correspond w T ith the holes required, and through which the drill is guided. These plates are located by some fixed line or lug on the casting, and then clamped fast, thus assuring exact duplication and rapid drilling, and avoiding the tedious laying out of the holes. In order to save changing the drill, it is desirable, if possible, to maintain the same size of hole on any given surface. Of course it is not always admissible to do this. MACHINE DRAWING 171 PLATE B. STEAM CYLINDER After the exact and complete development of the steam-end layout, the student should be pretty thoroughly acquainted with the details of the cylinder. All the work thus far has been entirely for his own information, to get his ideas in visible shape, so that he himself can have a permanent record of them. This layout, how- ever, is not in suitable form to finish up into a detail drawing. Its sketchy nature and the confusion of parts, especially if attempt were made to add dimensions, would render it somewhat difficult to be read by a workman taking it up as an unfamiliar subject. Hence it is now necessary to separately detail the parts, with the object in view of transferring, in the simplest and most direct manner, specific information to the workman which will enable him to construct the several parts. It is not enough now that the drawing be clear to the man who makes it; it must be absolutely clear to the shop mechanic, who has no means of knowing the designer's plans except through the information which the drawing gives on its face. This requires that the draftsman should put himself in the workman's place, and forestall, by the explicit nature of his draw- ing, all possible questions which may arise in the shop. In this way only can he hope to avoid errors of construction and the con- tinual annoyance of endless explanation of his orders. Size of Plate. Plate B is to be a finished drawing, and the first thing to do is to lay out the sheet. The standard sheet for details which has been adopted is 18X24 inches trimming size, with J-inch margin all round, so that the working space is 17x23 inches. The rectangle for the title is to be laid off 2§ X4 inches in the lower right- hand corner, and must never be altered, either in size or position. This does not mean that other sizes are wrong, but once a standard system is adopted it must be strictly adhered to, both for artistic and commercial reasons. The scale to which the drawing is to be made is indicated in the title corner on every plate. Scales to be Used. The scales permissible for shop drawings in the United States are those readily derived from the common foot rule, such as full size, 6 inches = 1 foot, 3 inches = 1 foot, 1 J inches = 1 foot. These are the most common, most easily read from an ordinary scale, and one of these can usually be adopted. The student should learn to read these from an ordinary scale without MACHINE DRAWING 173 being confined to a special graduation. To do this it is not neces- sary to divide each dimension by 2, 4, and 8 to get half size, quarter size, or eighth size, and then lay down the result. For half size, or 6 inches = 1 foot, ^ inch on an ordinary rule represents 1 inch. Hence, each half inch may be read as 1 inch, and its subdivisions | 2 accordingly, thus : , I , For 3 inches = 1 foot, or q uarter ■ i i lMtl.hl.nl o , p , « For i l i 1 1 1 1 ' o size, | inch represents 1 inch, and looks thus : 1| inches = 1 foot, or eighth size, § inch represents 1 inch, and looks thus: o It is very easy to get accustomed to this, and it saves much time and trouble hunting up a special scale every time. The other allowable scales, less common, but sometimes neces- sary on large work, are 1 inch = 1 foot, f inch = 1 foot, \ inch = 1 foot, f inch = 1 foot, \ inch = 1 foot, and \ inch = 1 foot. To use these scales conveniently, special graduation is desirable. Blocking Out Plate. The general arrangement of the sheet, number of views, and approximate space occupied, should be blocked out first. This can easily be done from the original layout. In general, several cross sections are preferable to a single view, which involves many dotted lines. Dotted lines are very convenient for showing invisible parts of an object, but they are often abused, and the drawing of a complicated piece made indefinite and confused thereby. As already stated, a working shop drawing is solely to convey information to the workman at the least possible cost. A careful consideration of this will settle the question of the number of views necessary, their character, and the amount of dotted line work desirable. Never let the drawing become the master; always be master of the drawing. Do not draw an extra view if no use can be seen for it. Do not put in dotted lines if the detail is completely shown without them. Full lines, or lines which show visible portions, must, of course, be shown completely. Practice of Checking Dimensions by Measurements. The nature of the pencil work on Plate B should be the same as on the original layout; viz, sharp, definite lines and positive intersections. Above all things learn the habit of accurate workmanship, for it 174 MACHINE DRAWING will save many errors and a vast amount of time. The draftsman must check himself at every line he draws. Slight errors in scaling will often throw parts out of proper relation to each other, and inter- ferences, which the drawing does not show, will become apparent only when the parts get into the machinist's hands. It is dangerous practice to project across from one view to the other. It only takes a slight irregularity or spring in the T=square to vary the location of lines very perceptibly from wiiere they should be, and once out of scale from this reason it is almost impossible to work a view with any certainty. Rather than project across from view to view, the principal lines, at least, should be scaled off on each view, and it will be found that in the end time will be saved and greater accuracy secured. Complete Development of Different Sections. It is not econ- omy of time to finish one view before beginning another. It is better to take some single detail of the drawing and develop it in all views, in order to study it from. all sides. What is completed in one view may be found to be totally wrong when developed from another side, and the time spent on the first view will be wholly wasted. For example, in the present case the steam ports should be drawn in side elevation, end elevation, and plan, and when thus completed the mind can leave them and in a similar fashion take up the study of the flanges, then the cylinder foot, and so on. Thus again the draftsman is master of his drawing, for he is continually making it tell him whether he is right or wrong. If, on the contrary, he allows himself to look at but one side at a time, and works from that stand- point alone, it may lead him into many difficulties from which he cannot readily extricate himself. Do not be afraid to use the eraser. The draftsman who hesi- tates to draw until he is positive that no change will be necessary, is likely to spend the greater portion of his time in unprofitable dreams, for he is attempting the impossible. A drawing is a means, not an end; and, as has been already pointed out, it greatly assists the draftsman in clearing up many doubtful questions which the imagination alone cannot do. A bold attack of a problem shows the quickest path to its solution, even if lines must be erased again and again. It is a sign of serious lack of ability to hesitate in the use of pencil and eraser. MACHINE DRAWING 175 Clearness of Drawings an Important Point. Attention is called to the simple, straightforward character of Plate B. Notice the almost entire absence of dotted lines; the enlarged section through the ports, giving ample opportunity for dimensions without con- fusion; the use of a half end elevation and a half cross section — the one to make clear the flange and bolt layout; the other to show the -exhaust opening, the small auxiliary view T s (drawn at convenient points) of the exhaust flange layout, the cylinder foot, and the drip boss. A steam cylinder is a fairly complicated casting; and it would be an easy matter, by the use of elaborate views, the dotting in of parts already completely shown, and careless linework, to rob this drawing almost entirely of its clearness and directness of illustration. Just ichat is necessary (for clearness' sake) and no more (for cheap- ness' sake), is the whole matter in a nutshell, and is what determines its shop and commercial value. Dimensions and Letters. A good line drawing can be spoiled by poorly arranged dimensions and hasty lettering. The five prin- cipal points to be kept in mind to develop excellence in this respect are: (1) system; (2) accuracy; (3) clearness; (4) completeness; (5) character. System. The habit of system in placing figures and letters on a drawing is the one element which, to a large extent, controls all the others. If the systematic habit is established early, the other requirements will be fulfilled more easily. A haphazard method will, on the contrary, just as surely prevent the successful cultivation of the ability to figure a drawing. In fact, if the haphazard habit is continued it will itself, by the dissatisfaction which it causes, soon compel the draftsman to change his occupation. In the first place, whatever part of a machine detail is to be dimensioned, that particular part should receive attention until it has been completely figured. Do not jump from one point to an- other, putting in a figure here and another there. Stick to one thing until it is done. For example, take Plate D and the simple detail of the steam pipe. Suppose we start with one of the square flanges. The first question is: "Where is this flange located?" This is answered by the dimensions 5-inch and 21-inch centers, which refer the face of the flange to the center of the pipe and the flanges to each other. 176 MACHINE DRAWING The next question is: "What are the three dimensions of the flange — length, breadth, and thickness?" This is readily answered as shown on the drawing. The next question is: "What further de- scription is necessary to completely specify the shape of the flange?" This is answered by the radius of the corners, J inch R. Next, "What drilling or special feature exists in the flange?" This is answered by \ J-inch drill, 3 J-inch centers, and the letter / to denote that the face is to be finished. The round flange of this pipe is approached and figured in the same way, except that the location of the face is preferably referred to the face of the square flange by the figure 8J inches, instead of to the center of the pipe, because the planer hand will more naturally use this figure. These flanges are now to be connected by a pipe involving two sizes. The main pipe is 3 inches diameter inside, 4 inches outside, and \ inch thick, running into the two branches by fillets and radii, as figured. The two branches are really one pipe, 2\ inches inside, 3J inches outside, J inch thick, and sweeping down into the square flanges by 4-inch radii. This systematic method takes longer to explain than to actually execute, but it is typical of the train of thought which must be followed on all pieces, simple or complicated, in order to properly place dimensions. In general, it may be stated that all parts of a piece must be referred either to each other, or to some common reference line, or to both. Each part so referred must then be figured as a piece by itself, and then its connections to the principal structure. Thus, figuring a machine detail involves three things: (1) relative location of its parts; (2) proportions of these parts; (3) proportions of con- necting members. As in the original design of a piece, so in the figuring of it the draftsman must as far as possible put himself in the place of the workman, judging the methods and processes of construction and available tools. This will largely influence the arrangement of the dimensions. Of course it implies considerable experience in shop work, which some students do not possess. He can begin none too early, however, to learn to look at his work from the shop stand- point, and surely make it some better on that account. MACHINE DRAWING 177 Pieces must not only be systematically dimensioned, but regularly specified and called for by suitable titles. A title should specify at least three things: (1) name of piece; (2) number wanted for one machine; (3) material. To these might be added a fourth; viz, pattern or piece number. The latter is not specified on the drawings under discussion, because systems of pattern and piece numbering are so varied that little would be gained by developing one for this special study. These titles should always be put on in the same way, as the workmen become used to a certain system and are likely to mis- understand directions if a regular plan is not followed. A good way to arrange titles is suggested on the plates, although there are others which might be used. Bolts are usually specified by diameter and length under the head, the length of thread being determined by some standard system in use by the shop, unless otherwise called for. Bolts are specified on the sheet containing the piece into which they are tapped. In the case of through bolts, tapped into neither piece, they are preferably called for in connection with the principal member. Accuracy. Of course the dimensions on a drawing must be accurate. It is, however, a very easy matter to make errors. To insure accuracy a figure must never be put down carelessly, and a constant watch must be kept that scaled figures add up to over-all dimensions. It will not do to rely upon scaling alone, as a very slight variation from exact scale may throw two dimensions out with each other. In spite of all the care that can be exercised errors will creep in, and a final thorough checking must be given a drawing before it is pronounced complete. A good rule to follow in checking up is to ' 'assume everything wrong until it is proved to be right." Clearness. As in the line drawing itself, there must be abso- lute clearness of instruction by the dimensions. Any doubt as to what a figure is, or what it means, rules out that figure as part of the drawing. If a piece is made wrong because doubt of this char- acter is transmitted to the workman, the draftsman is always held responsible for the error. Figures should, in all cases, be placed where they can be most clearly read. They should be bunched on a single view as far as possible, but not when greater clearness demands that another view 178 MACHINE DRAWING be used. It hinders the reading of a drawing materially if the eye is forced to jump over large spaces of the sheet from view to view, to catch the several dimensions of a small detail. Usually it is easy to so group figures as to avoid this. It is a good plan to keep dimensions off the body of the draw- ing, when it can be done so conveniently. It is not worth while, however, to go out of one's way to do this, as figures in the open spaces of a detail do not at all destroy its clearness. Extended notes on a drawing to make it clear should not be required, but they should be used without hesitation if any doubt exists. An explicit note of instruction is the final resource for clearness when the art of drawing fails of its purpose, as it some- times does. Completeness. A detail is completely dimensioned when it shows all the figures necessary for the workman. Anything short of this is incompleteness. As modern shops hold the draftsman solely responsible for the design, the mechanic is not allowed to modify it by filling in any omitted dimensions. The only way to be sure that all the dimensions are on is to systematically go all around a piece inside and out, according to the method suggested under the paragraph on "System". It is a good plan to always bear in mind that not only the machinist is to use the drawing, but also the pattern maker. For the benefit of the latter, special attention is desirable in figuring the cores. This saves him some addition and subtraction. In general, it has been found that less chance of error exists if mathe- matical work is not required of the shopman, all necessary data being furnished on the face of the drawing. Character. By character in figures and letters is meant uni- form style, height, and slope, and a certain boldness peculiar to the work of the expert draftsman. The last is difficult for the novice to acquire. The student should not be discouraged because his efforts do not look like impressions from printers' type. Artistic excellence is the result of long experience, but is based on character. If the student can once get character into his work, the artistic feature will, with careful and constant practice, gradually develop. It is safe to say that there is no one element of a drawing which more positively stamps it as the work of an amateur than the char- MACHINE DRAWING 179 acter of the lettering, and every attention should be paid to getting out of the apprenticeship stage in this respect. Freehand lettering only is permitted in the drawings illustrated herewith. Ruled letters are seldom found on any working drawings, as the element of time involved is so great that few shops are willing to pay for it. Uniform style requires that if capitals only are used in titles, they only must be used in notes and elsewhere on the drawing. If lower-case letters are used, they must be used in every part of the drawing. One style should not be mixed with another. The height of the letters should be limited by two horizontal lines, and though practice may render the upper line unnecessary, it takes but an instant to draw it, and uniform height is then assured. A good height for titles of details such as are illustrated is & inch. The height once chosen should be adhered to throughout the whole set. A medium, not a hard, grade of pencil (3H) will give the hand greater freedom. A great temptation exists to omit titles from the pencil drawing, simply inking them on the tracing. This is false economy of time, for in the end it will be found that enough time will be saved by the certainty with which the tracing can be made to more than pay for the labor on the pencil drawing. Again, it permits the tracing, in regular shop practice, to be made by cheaper labor than that which produced the pencil drawing. Uniform slope is most easily acquired by the use of guide lines put in at frequent intervals. A small wooden triangle can be made, giving the required angle. The angle of the letters shown on the plates is 9 degrees, or about 1-inch slope in 6 inches. The question as to whether letters should incline backwards, forwards, or stand vertical, does not enter this discussion. Character is not affected by the slope. The student may choose whatever comes most natural to him, but having chosen, the character of his work will be spoiled if he varies it. The most difficult of the three is the vertical style; hence most draftsmen incline their letters. The backward slope is used on the plates of this shop drawing paper, thus giving the student opportunity to compare with plates in the earlier books, and follow his preference. The effect of change of style, height, and slope is shown in Fig. 122. Attention is called to Fig. 123, which is a sample title, in which these points are corrected. 180 MACHINE DRAWING Principal Titles. The principle title of a drawing should con- tain at least seven items: (1) name of principal details shown; (2) name of machine; (3) firm name Sir AM OYUNDLK \K-j&-\V. UvipVax Vum^ STL AM CYl.lNPEB. " \6-«V-\g PUPlhX PiUsAVl Fig. 122. Sample Titles Showing Effect of Non-Uniformity of Lettering and location; (4) scale of draw- ing; (5) date of completion; (6) draftsman's signature; (7) filing number. To these are often added others, but for purposes of filing and reference the above at least must be put on. The filing num- ber may or may not be put in the title frame, but it is really a part of it. It is often put in the margin below the title. An arrangement of title should be established and then followed exactly, without variation either as to location on sheet or detail make-up. Abbreviated words are always permissible in titles, provided the meaning is clear. Special care must be taken in punctuation, however, as a title, whether abbreviated or not, has an unfinished appearance if the periods, commas, and other necessary punctuation marks are not included. The sample title illustrated in Fig. 123 indicates the arrange- ment chosen for the drawings of Part I. Note that in this special Fig. 123. Sample Plate Title Properly Drawn case the residence of the student draftsman has been substituted for the file number of the drawing. This style of title must be put with care on every drawing, MACHINE DRAWING 181 even on the rough pencil layouts. In the latter case it may of course be left in pencil, as the rough layouts are not to be inked. Inking and Tracing. Both bond paper and tracing cloth are used in business practice for finished drawings. It is desirable to keep a stock of both in any drawing office, so that either may be used as occasion requires. Bond paper stretched on the board gives a beautiful surface to take the ink, and very handsome and effective detail or assembled drawings can thus be produced. Changes are not quite as readily made on bond paper as on tracing cloth, and it takes a little longer to make the blue print. In other ways the bond paper is not quite as flexible to use as the tracing cloth. However, one must be guided entirely by shop con- ditions to settle the question of preference. As the tracing cloth is generally used, and suits the purpose of the student better, it will be required in this work. Preliminaries. The inking should be done on the rough side of the cloth. One reason for choosing this side is that as the cloth tends to curl under toward the glazed side, the drawing as it lies right side up will tend to straighten itself. This seems to be a small point, but it is a very important advantage for filing and for the convenience of those who are to handle the drawings. Also the rough side takes colors and inks better than the glazed side. To trace on the glazed side is not wrong, for it is often done, but it possesses no advantages of its own, and has the disadvantage men- tioned above. Chalk dust scattered over the surface of the cloth after it is tacked down will remove the slightly greasy coating which prevents the ink from flowing well from the pen. This is always necessary if the glazed side be used, and usually for the rough side. The chalk must be carefully removed from the cloth before inking. Rules for Inking. The first step in inking is to draw the center lines. Remember that accurate intersections are of the utmost importance. No circle is complete without two intersecting lines, preferably at 90 degrees, to determine its center, and these lines should be inked before the circle. When this is done, a definite point exists for the needle point of the compasses. If the circle is drawn first, the needle point may not be placed accurately at the center on the pencil drawing beneath, thus throwing the location out. 182 MACHINE DRAWING Likewise the principal center lines of pieces, the lines around which the pencil drawing was built up, should be at once put in. The main body of the drawing, the full lines, should be taken next. In general, circles and arcs should be inked first, but there are cases where it is easier to run the arcs into the straight lines than to match the straight lines to the arcs. These are exceptions, however, and can be judged only as the case arises. Straight lines, horizontal and vertical, should be inked with the T-square and triangle in position. It is a common practice to dispense with the use of the T-square entirely in inking in, using the triangle to match the lines to the arcs already drawn. A neces- sity for this implies very poor work on the arcs, for with any reason- able care true horizontal and vertical lines will match the arcs all right. With regard to time required, the accuracy with which the T-square may be brought up to a line, or the triangle set on the T-square, more than makes up for the time gained in even an approxi- mate setting of the triangle without a guide. It is just as easy to cultivate the habit of holding the T-square and triangle with the left hand and the pen with the right, and draw an exact line, as to lapse into the other method, which is not workmanlike. The lines of the body of the drawing depend for their width upon the size of the detail. For a large piece they may be j% inch wide, and the shade lines & inch. For a small detail such widths would be too great. Remember that contrast is the principal aim, and to produce it is the only reason why we use different kinds of lines on a drawing. Hence the greatest care must be exercised to prevent body lines from becoming confused with center or dimen- sion lines, and vice versa. Also thick lines are desirable for the production of a bold blue print. Shade Lines. Shade lines certainly improve the drawing from an artistic standpoint, and the student has been shown in Machine Drawing, Part I, how to put them on when desired. Whether or not it is desirable to adopt them on all working drawings is not the purpose of this book to decide, or even discuss. Almost always drawings can be made perfectly clear without them, and are so made and satisfactorily used in probably the majority of shops. Some shops are willing to pay for the extra time necessary to put on shade lines; this, however, is purely their own investment. MACHINE DRAWING 183 Crosshatching. Cross-section lines are usually drawn at an angle of 45 degrees with the horizontal, and on sections which are adjacent to each other the slope should be in different directions. If three or more sections come together, the width between section lines can be so changed as to indicate clearly the different parts. An example of this is shown in Fig. 124. The spacing of section lines must not be too fine, rarely closer than Ye inch, more often from A to f inch, else the labor involved is too great and uniformity practically impossible. It is a waste of time to rule in section lines on the pencil drawing; they may be sketched in freehand, as shown on the original layout of the steam cylinder. Even spacing concerns the tracing alone, and the student should train his eye to regularity as he traces. The thick- ness of section lines may be intermediate between that of center lines and the body lines of the drawing. Inking Dimensions and Letters. Ex- tension lines may be dotted, as explained in Mechanical Drawing, Part III, or they may be fine, full lines, the latter method being illustrated in the series of pump plates in this paper. Dimension lines are also often made fine, full lines. If these lines are made full they should be made as fine as it is possible to draw them and still have them firm, clear lines. The same width should be used as for center lines. Character in inked figures and let- ters is more difficult to attain than in pencil work. In the first place a pen suitable to the style of drawing is necessary. A civil engineer's fine mapping pen, which gives character to his drawing, is not desirable in producing the bold character of a machine drawing. For the latter, choose a rather stiff, blunt pen which is not "scratchy," but runs smoothly, making a line of uniform width. A pen with a round, or ball-shaped nib, now on the market, answers the purpose well for ordinary details. A bold, free stroke should be made with the idea of producing a smooth, even line, finished at the first trial. The Fig. 124. Section Showing Varia- tions in Crosshatching 184 MACHINE DRAWING hesitating uncertainty of the beginner's hand produces a "shaky" letter, and going over a letter or figure twice or more to smooth it up usually makes it worse. Figures and letters which are broad in proportion to height are easier to make, and have more character. It should never for a moment be forgotten that uniform height and slope carefully followed will develop character and quickly lead to artistic excellence. Foot and inch marks are often put after figures according to the common usage. In cases where feet and inches are expressed, thus: 3'-6", or 4'-0", they are, of course, absolutely necessary, and the dash between the figures must be very positively indicated. In cases of inch dimensions alone the marks may be put on if desired, but where there can be no doubt that inches, and not feet, are meant, the inch marks are not necessary. Abbreviations. A list of the most common abbreviations in use on working drawings follows. This list has been adopted for the plates in Machine Drawing Part I : F. A. O finished all over. / finished surface. R radius. D diameter. R. H right hand. L. H left hand. P. R piston rod. P. TAP pipe tap. CTRS centers. C. I cast' iron. S. C steel casting. Bz bronze. C. R. S cold rolled steel. T. S tool steel. O. H. S open hearth steel. W. I wrought iron, PLATE C. PISTON ROD AND VALVE STEM Specifications. The piston is of the one-piece box type, with sprung-in rings. The width is reduced to 4J inches at the outside, so that if the piston strikes the cylinder heads it will not tend to spring and break off the narrow ridge of metal outside of the packing ring. The piston rod is fastened to the piston on a taper drawn in 186 MACHINE DRAWING by a nut, and the nut is checked by a J-irich split pin. The packing rings are prevented from slipping round the piston by lugs fitting loosely in chipped recesses in the groove. These being at opposite sides for each groove, the leakage of steam through the split in the ring is minimized, for it must pass halfway around the piston before it can pass through the split in the other ring. This is a simple, but fairly effective, device. The packing rings are usually cast in the form of a cylinder of some length, turned to a diameter a little larger than the cylin- der bore, cut off to the required width, and sufficient space cut out to permit being sprung in to the size of cylinder bore. The location of the spool on the piston rod is not positively known, as the setting of the valve bracket may be slightly differ- ent from what the drawing calls for. Hence, instead of a dimension, the words "measure for" are put on, to indicate that the spool be located during the erection of the pump. The hexagonal flanges of the spool are convenient to hold the rod from turning while screwing on the piston and plunger nuts. Molding and Machining. There are no special features con- nected with the molding and machining of parts on Plate C. The holes in the piston side walls are necessary to give supports for the core, the piston being cast on its side. These holes, after the core is cleaned out through them, are plugged as indicated. PLATE D. STEAM CHEST AND VALVE Specifications. The steam chest in this instance is located on the cylinder by fitting down over the ledge made by the valve seat. The side flanges also serve the purpose of guiding the valve. It will be noticed that the steam-chest cover is 15 J inches X llj inches, while the steam, chest is 15 inches X 11 inches. This allows a ledge of | inch, all around which the cover overhangs the walls of the chest. The steam cylinder flange in order to correspond must like- wise be 15 J inches X 11J inches. The reason this is done is because of the difficulty of making good matched joints between the cylinder flange, chest, and cover. The practice of thus leaving a little ledge all around is by no means universal, and often the irregularity in the joints is smoothed off by chipping. This is the case with the other flanges on this pump. The steam chest, however, was thought less —1 --*H ] ■ ■* 1 . .£ L 188 MACHINE DRAWING likely to match properly, and the slight overhang gives the finished appearance of a sort of beaded edge. The valve is what is known as a "square" slide valve. This means that when the valve is placed central on the ports its work- ing edges are "square" with the ports; that is, in exact line with them. If the valve be moved either way from this position, the slightest travel will admit steam to one end of the cylinder and exhaust it from the other. (See Plate A.) Another way of stating this is to say that a "square" slide valve is a slide valve without "lap". The valve is driven from the valve stem by the striking of the nuts against the lug on its top. Since the valve is already guided on its edges by the steam-chest flange, the valve stem, to avoid springing, must be perfectly free in the slot cast for it, as is shown by the f-inch radius of the bottom, the stem being 1 inch in diameter. The steam-pipe flange is made square to keep the height of the chest as low as possible. The radius of the bend should be ample; in this case 4 inches is considered sufficient. The exhaust tee must have its upper flange high enough so that the chest cover can be lifted and slipped off the studs without interfering with it. The lower flanges should be made wide enough to permit the tap bolts to be put in without striking the 4-inch vertical pipe, 5-inch centers being necessary. The J-inch drip-cock, as located, readily drains the steam chest and exhaust passage of both cylinders, as well as the exhaust tee. Molding. It is evident that the steam chest will be molded in the position shown on the drawing. The parting line of the mold will be through the centers of the steam-pipe opening and the stuffing-box. These holes must be cored out. The main body of the chest could be made to leave its own core, but it may not be made in this way. It may be cheaper to fashion the pattern solid, and make one large core-box for the inside. In this way the pattern will probably hold its shape better and require less repairs, than if it were made in green sand. The core-box will be an extra piece to make, but it probably will cost no more than to carve out the inside of the pattern, and is a rather more substantial job when done. The molding can be satisfactorily done by either MACHINE DRAWING 189 method, shop conditions being the controlling element. As far as the labor of molding alone is concerned, the first method is prob* ably easier, as it saves handling large cores. The other parts in Plate D are very simple in their molding, and require no special attention. Machining. Most of the surface work on this plate is adapted to the planer. The slide valve may, perhaps, if finished in lots of considerable number, be more satisfactorily handled on the milling machine. The final finish of the face of the valve must be a scraped fit to its seat. The drilling of the cover and pipe flanges is to actual layout on the casting, or preferably, through jig plates. A templet for laying out is at least desirable, even though the expense of a jig plate be not deemed necessary. < PLATES E AND F. VALVE MOTION LAYOUT General Specifications. These plates represent the layout of the valve motion, and are necessary in order to find the length of the levers and rocker arms. It will be noticed in Plate F that the valve stem of one side of the pump is controlled by the movement of the piston rod of the other side, the proper direction of motion being given to the valve by placing the rocker shaft above or below the valve stem as required. By reference to Plate A it will be further noticed that the nuts on the valve stem inside the chest, which abut against the faces of the lug on the valve, do not rest against the faces of the lug in the position shown, but have considerable lost motion. This lost motion is one of the essential features of the valve motion of a duplex pump, and permits the valve to remain at rest for a short period at the end of the stroke, though the valve stem may have reversed its motion and begun its return stroke. ^Yhen this lost motion is taken up by the movement of the stem and the nuts abut against the lug on the valve, the valve will move, and from this point to the end of the stroke be positively controlled by the motion of the stem. At the end of the stroke the stem will reverse, when the lost motion will again permit the valve to rest for the same period as at the other end, and then move on as before. The time of rest of the valve, and consequently the pistons and plungers, is approximately one-third the period of the stroke. This 192 MACHINE DRAWING means that the piston on one side travels one-third of its stroke before it picks up, through the valve levers, the valve on the other side. During the second third of its travel it is bringing the valve to the point of opening. During the last third of its travel it is opening the port, wider and wider, to steam. Thus the opposite piston will start when the first piston has covered two-thirds of its stroke, and there will be only one-third of the stroke when both pistons are moving at the same time. This relative period of rest to motion is not always made in this exact ratio, but is at least approximate to it. The period of rest at the end of the stroke is to allow the water end to adjust itself quietly to the reversal of motion about to take place at the end of the stroke. When the plunger stops, the water valves must be given time to seat themselves, and the flow of water through the passages checked. It is much easier to start the flow in the opposite direction if the reversal of plunger motion is not instan- taneous. Hence for handling long columns of water, which, once in motion, tend by considerable energy to remain in motion, the duplex pump by this peculiar delayed action has been found to be well suited. Travel of Valve Stem. It will be found that for complete uncovering of port, and motion divisible into thirds as described, the travel of the valve stem should be three times the width of port, or 3 X J = 2f inches. A little more than this is allowed, and the travel made 2| inches in this case. Referring to Plate E, this dis- tance is laid off as shown by the two limiting vertical lines across the line of the valve stem, the central vertical line of mid-position being drawn. The problem then is to find such centers for the rocker arms that the travel of the piston-rod spool will, through proper leverage, produce travel of the valve stem between these two vertical lines. This can readily be done by a few trials, the only requirement for this case being that the extremes of the arc of swing of both piston-rod lever and rocker arm shall be equally above and below the center of piston rod and valve stem, respec- tively. The greatest possible travel of the piston-rod spool, 12 \ inches, is usually laid out in this case, not the nominal 12 inches. Length of Levers and Arms. From this layout the lengths of the levers and arms may be scaled off for the detail drawing, also the MACHINE DRAWING 193 location of the rocker-arm centers. The student has the former given him on Plate G, but the latter, which is necessary for the development of Plate H, must be determined by his own layout. Plate F must also be laid out before developing the cross section of the valve bracket. Stuffing Boxes. The design of stuffing boxes for both steam and water ends, and the length of the yoke, should be determined next. A safe method of assuming clearance between the spool and the gland studs at the end of the stroke is to imagine that the gland stud nuts have accidentally worked off the studs, so that they are about to drop. They are thus shown by dotted lines on Plate E. A good clearance, say \ inch to \ inch, is then allowed, and the gland drawn in. The length of the gland is determined by the number of rings of packing necessary in the stuffing box; it is usually pro- vided that the gland may compress the packing to about one-half its original depth before bringing up against the face of the box. Packing f-inch square will do for this size of piston rod, hence the faces of the yoke are easily determined, and its detail, with the stuffing boxes, proceeded with as on Plate H. The length of yoke may be brought to an even figure; and proceeding on the above plan the length can be conveniently made in even inches without any fractions; viz, 28 inches. It will be noticed that the stuffing-box flanges serve to center the yoke in line with the steam and water cylinders. This is a desirable feature of construction, and forms a simple and easy method for lining up the steam and water ends. PLATE G. VALVE MOTION DETAILS Piston=Rod Levers. The piston-rod levers on this plate are specified to be steel forgings. Forgings of this kind are expensive, but are light, neat, and reliable for the important service which they have to perform. Castings, whether steel or iron, are much cheaper, and perhaps more commonly used for this detail. When sound they are equally serviceable, though of more clumsy proportions; but the danger in castings of this form is the existence of hidden flaws or pockets, which frequently occur at the points where the hub or the fork joins the arm. These flaws cannot be readily detected from the outside, and breakage may occur at some 0- c "3 u- z -1 Mi o o i i-j CJ *" h- j o £ o O 2 o >T 4. in 4. a ij fv K X ■? -; \ti o o j «.•' > <4 <£ ?> i MACHINE DRAWING 195 critical time, when the disability of the pump may be a serious matter. Dimensions "Out of Scale". It will be noticed that on the detail of the "link pin" two of the dimensions have a short "wavy" line beneath the figures. This is one of the several ways of indicat- ing that the dimension is "out of scale". Some draftsmen use a straight dash beneath the figure; some draw a circle about it; some print after the figure, "out of scale". Although workmen are not allowed to scale drawings, but are required to "work to figures only," yet for general safety's sake, and for the sake of the draftsmen who consult the drawings frequently, attention must be called to any variation of the figure from the measured distance on the drawing. Nothing makes a workman, or any one else who reads a shop draw- ing, lose confidence in it more quickly than to discover that it does not "scale"; but when no indication exists that the draftsman himself is aware of it, then every dimension is viewed with doubt and hesitation, and the drawing becomes practically worthless. Dimensions seldom should be out of scale; but if they are, through error or necessary change, a carefully worded note should be added. Molding and Machining. No special features of molding or machining are noteworthy on Plate G. PLATE H. YOKE, STUFFING BOXES, BRACKET, ETC. Having worked up the layouts of Plates E and F, the student has enough information to proceed with Plate H. This, like Plate B, is without dimensions, the student's work being to make the drawing and fill in the necessary shop data. Specifications. The valve-lever bracket is bolted down to its lug on the yoke through holes larger than the bolt, thus permitting slight adjustment. When the proper location is determined, the bracket is positively fixed in position by two dowels, \ inch in diam- eter. The holes in both bracket and yoke are drilled through both pieces at the same operation. This very common method of fixing bolted parts of machinery in absolute position not only assures firmness, but also in case of removal, permits the part to be readily and positively replaced in its exact original position. If possible, the steam cylinder cricket should be of such height that the stone or brick work upon which it rests shall be at the MACHINE DRAWING 197 same level as that beneath the water cylinder. The tapped holes in the top surface receive bolts from the cylinder foot. These bolts are often used only for shipping purposes, the cylinder foot when the pump is set up being allowed to slide freely on the cricket, thus permitting free expansion and contraction. In such cases the water end is rigidly fastened to the foundation by holding down bolts. Molding and Machining. The valve lever-bracket would most naturally be molded with the axes of the shafts vertical, the parting line of the mold being the center line of the middle web. This makes quite a long "draw" for the shaft bosses, but the ample taper on the outside overcomes this difficulty. The space between the side webs leaves its own core. The shaft cores stand on end in the mold, which is the best position for strength and stability. Another method is to have the parting line of the mold on the vertical center line of the bracket, as shown in the end view. In this case the bracket would be cast on its side, and cores must be set for each side of the middle web. The shaft cores are set as easily as before, but in this case lie flat. As with the steam chest, each method has its advantages, which depend largely upon existing conditions. As cored work is generally avoided whenever possible, the first method would probably be chosen. The shaft bosses are "chamber-cored," to save labor in boring, the bearing surface for the shaft being only a short distance at the ends. The chamber-core diameter should be enough larger than the shaft so that by no possibility can the cutter run into the rough scale, even if the hole be bored slightly out of line. If it should do this, the labor of caring for the cutters more than offsets the attempt- ed saving of labor. The yoke is simply a barrel open at each end, and with a piece cut out of its side. The inside evidently must be cored out, and the core is satisfactorily supported at the ends on its horizontal axis. The parting line of the mold may be either the vertical or horizontal axis of the end view, the only difference being that in one case the ledge for the valve bracket will "draw," and in the other case it must be loose on the pattern and "pulled in" after the main pattern is drawn. The cricket and stuffing boxes present no difficulties. The bore of the stuffing boxes and glands should be from ^ inch to rg inch MACHINE DRAWING 199 larger than the rod, to allow the fit to be entirely between the rod and the packing. The horizontal boring machine with a double facing head is adapted to boring and facing the yoke flanges. The drilling is accomplished as before by templet or jig. Attention is called to the tapped holes for oil or grease cups on the valve-lever bracket. The holes on the lower boss cannot be drilled strictly as shown, because the drill shank will not clear the upper boss. They should be swung around the boss at such an angle as will allow the drill to clear. This is a good instance of the common error of drawing details which cannot be made, and constant watch must be kept to avoid such mistakes. PLATE I. WATER END LAYOUT Specifications. In the preceding work, the completed plates were used to assist the student in developing the layout drawings for other parts of the pump. In this Section, Plates K and L„ being given in full detail, offer a good start for the development of the water cylinder, which is the purpose of. Plate I. As before, work should begin at the inside and progress outwards. Thus the piston rod with its nut should be drawn first, the hub of the plunger built around it, then the plunger barrel, the bushing, and ring to clamp the bushing. The limits of the plunger travel should be sketched in, and the valve outline shown, in order to determine clearances. The progress of Plate I is on exactly the same basis as that stated in detail for the steam cylinder layout; hence it need not be repeated. . Plunger and Bushing. The points controlling the design of the water end must, however, be studied to enable the student to work intelligently. The fit of the rod into the plunger hub is loose, te -inch play being allowed, in order to permit the plunger to be guided solely by its bushing, and thus be independent of any change of alignment of the piston rod. The relative length of plunger and bushing should allow the end of the plunger to overrun the edge of the bushing at the ter- mination of the stroke, to prevent the formation of a shoulder. The bushing is made of brass because of the better bearing of the two dissimilar metals, brass, and iron. Of course there is no lubri- cation except the, water, and the dissimilar metals tend to "cut" 200 MACHINE DRAWING less than if both were alike. The brass bushing also prevents the plunger from "rusting in" in case of long periods of disuse. The bushing being of expensive material is made as light as possible, hence it has no stiffness of its own. Therefore, it is reinforced by a deep cast-iron ring, which also takes the bolts and clamps the bush- ing tightly to its ground seat. These stud bolts are usually made of "tobin bronze," a rust-proof material, possessing strength almost as great as that of steel. This arrangement permits ready removal of the bushing when necessary. Hand Holes. As the parts of the common pump valve illus- trated in detail on Plate L must be often replaced during service of the pump, provision must be made for unscrewing the stem and substituting a new one. This must be done through the hand holes provided on the cylinder. The lower valve deck must be located so that the inner valves when unscrewed will not strike the clamp ring. As shown in Plate I, the clearance is pretty small, almost too small, but as it affects only two valves, it will probably cause no inconvenience. No hand holes are necessary for the end chambers, as access to the valves is had by removing the outer heads. Deck Details. The upper deck may be placed at a height giving sufficient clearance to allow the upper nuts of the clamp ring to be unscrewed with a socket wrench from the end of the pump. These decks are subjected to a severe pounding from the pulsations of the pump, and should be amply strong; If inches is deemed thick enough for this case. The middle transverse wall may be 1J inches thick and the middle longitudinal wall a little thinner, about 1J inches. With high pressures these walls, being flat surfaces and the valve decks likewise, are likely to fracture under the heavy pounding. To avoid making them excessively heavy they are often strongly ribbed, either on the inside or outside, usually the former. The curving side walls are of better form to withstand pres- sure, and need not be as thick, 1 inch being sufficient. This can be decreased to f inch in the suction passage below the deck, where little pressure exists. Outer Head. The outer head is also considered strong enough at 1 inch thickness, on account of its curved shape. It requires J -inch studs. Studs are preferred to tap bolts in this case, as in all MACHINE DRAWING 201 other similar cases, on account of the frequent unscrewing of the nuts for purpose of removal. One or two unscrewings of a tap bolt in cast iron will destroy the tightness of the thread, while the stud, being steel, stands the wear better. Valve Seats. The valve seats are taper screwed into the deck; they are sometimes forced in on a plain taper fit. They are located as closely as strength of the deck between the holes will permit. It is not well to place the edge of the valve closer than \ inch from the cylinder walls. The valve holes in the lower deck should be in line, or nearly so, with- the holes in the upper deck, in order to allow the shank of the mill to pass through when milling the lower holes. Miscellaneous Details. The suction opening is 7 inches in diameter, 12J-inch flange, 10|-inch bolt circle, f-inch tapped holes. By means of the hand hole at the end of the suction passage, any dirt which may have been brought in through the suction pipe may be removed. The water cylinder cap, discharge ell and air chamber may be laid out from the detail Plate K, and the student must do this to see that the parts actually go together properly. With the foregoing discussion the student should be able to produce Plate I, which is the preliminary step to the detail drawing of the water cylinder as shown on Plate J. PLATE J. WATER CYLINDER Complications in Design. The water cylinder is, perhaps, the most complicated detail that the student will meet in this set of plates. Fundamentally, it is simply a box with curved sides, divided by the several walls into five compartments, each of which communicates with the outside by a round nozzle or flange. If this basic idea be kept constantly in mind, the student will have no trouble in building up the detailed design. This fundamental conception of a complicated piece is a very important idea, and should be developed carefully by the student. It is one of the great secrets of good design, both from an artistic and a commercial standpoint. We often see a machine which seems to begin anywhere and end nowhere; it appears to be a miscellaneous collection of bosses, lugs, ribs, and flanges. There is no general MACHINE DRAWING 203 prevailing shape to the structure, no harmony of the lines. This is because the designer, if he may be so called, did not have the funda- mental notion of shape, to which all minor details should have been subordinated. He simply grouped parts together, without con- sidering the fundamental structure. In this water cylinder the box is the basic part of the structure, and its lines must be first developed; they should be designed to convey a smooth, regular, and consistent surface to the eye. Then the nozzles and flanges may be added as subordinate parts; they will merely interrupt, but not destroy, the prevailing outline of the box. The dotted lines in the cross-section views of Plate J show the general shape behind and beneath the nozzles. The hand holes are the same as on Plate K, and the detail of the cover should specify the number required for both places. Provision for draining the four chambers of the water cylinder is made by the f -inch pipe tap holes at the lower deck, and the cap, likewise, by the single hole at the upper deck. Drip cocks are screwed into these holes. The holding-down bolts should not be less than 1 inch diameter ; 1| inch would perhaps be better; and the holes in the foot should be drilled at least J inch large. Dimensions. It will be noticed that this plate has dimension lines, but no figures. This is because the cylinder is rather difficult to figure, and it is desired to guide the student in arrangement of the figures without lessening the benefit of his study of them. Special attention should be paid to this feature of the plate. Notice that although space for dimensions is restricted, a clear opening is always found for the figures; and when one view seems to offer no space for a figure, another view gives the desired opportunity. No finish marks or titles are shown on this plate, these being left entirely to the student for insertion. Molding. The centers of the curves for the sides being on the main horizontal axis of the nozzles, the cylinder, if molded to be cast vertically as shown, will draw readily both ways from this line. The exceptions to this easy draw are the foot, suction nozzle and flange, and hand-hole boss. On account of the inside of the cylinder being cored, these pieces if made loose on the pattern have ample space to be "pulled in" after the main pattern is withdrawn. 204 MACHINE DRAWING The suction passage below the deck communicates with the main core through the valve holes, hence it may be supported from the main core. This involves some difficulty, however. If a three-part flask be used, and another parting established at the center of the suction, flange, in addition to the previous one, the problem becomes much simplified. It is desirable to make the four chambers of the cylinder alike in general proportions. It is then possible to make a single core- box, and by the use of loose pieces change the length of the nozzle cores and transpose from right to left, thus saving labor on the pattern. This, however, multiplies the loose pieces on the pattern. The many pieces are likely to become lost and make frequent repair necessary. Hence it is not always wise to use a single core box too much, and good judgment is required to fix the limit. Machining. Special double horizontal boring machines are now in common use for such cases as this water cylinder. The centers are made adjustable, so that within limits any distance between piston-rod centers can be met. The advantages of double boring are, of course, most obvious for a considerable number of duplicate cylinders. It will be noticed that the face of the suction flange is carried out flush with the cylinder head face. This affords opportunity for finishing all the end surfaces at a single setting of the tool, whether the work be done on the rotary or reciprocating planer. This same point might have been observed on the small hand-hole boss at the other end of the cylinder, but the advantage gained did not seem to warrant extending the "reach' ' through the hand hole. PLATE K. WATER CYLINDER CAP AND AIR CHAMBER Specifications. For a water cylinder cap of this size, the most difficult problem is to find room for the hand-hole bosses. A hand hole 4 inches X 6 inches is about as small as can be used, and this calls for a flange at least 7 inches X 9 inches. These are the pro- portions shown on the plate, and since the boss overhangs the bolts in the* main-cap flange, it must be cut away underneath to clear the nuts. If three stud bolts are used on each side, this overhang also requires that the nut be "fed on"; that is, screwed on little by little CO &; 1 5 0- O -J ul (J PC X -J *** ex- X o o r o 2 J 5 p z O s 0- UJ DC K O o i o .{•< > o & CP ^ g j -^ — e uJ -3ottom i^r a ru.rns *r.My **""""*>»<"» WJ ,l6Ta.rns op./^"sUcl we ro F <*>/*' 7Tu.rr>sofl02 steel*,™ top Uyty IOtz"_ L 228 MACHINE DRAWING be drawn to a very large scale, such as twice the size, in order that all dimensions may be shown without sacrificing clearness. In this section it should be noted that several diametrical dimensions are given and that the dimensions of the slot are shown along with the corresponding dimensions of the coil. Side View of Assembly in Armature Core. A side view of the coil assembled in the armature core is next shown, Fig. 8. This view shows a number of details which are covered completely with very little labor. For instance, the binding wires are shown and described completely, although nothing more than a section is drawn. This illustrates very well the use of good explanatory notes and their value as labor savers. This view also shows the armature flanges and determines their general dimensions, as related to the coils. Another point in connection with this drawing which should be given attention is the method of calling for the various parts. It will be noted that a table is included in the lower right hand corner. This table gives on the right the name of each part, with a number which refers to a corresponding number in the body of the drawing. Note that these numbers on the drawing are made large and enclosed in circles, and that arrows are added where necessary to call attention to the proper part. The table contains, still farther to the left, the proper material to be used and the number of parts required. Such tables are used by some drafting rooms and undoubtedly prevent confusion due to placing too much data on the body of the drawing. Another point should be noted. The drawing is made pri- marily to show the armature coils, and to do this we have a plan, a side elevation, and a section. The plan and elevation do not bear the relation on the sheet that the laws of projection require, but nothing in clearness is sacrificed, space is saved, and the drawing is really made easier to read. In addition to showing all necessary details of the coils, suf- ficient data is given from which to make the next drawing. In other words, we have determined enough of the physical dimensions of the armature flanges to know how they must be built to support properly the ends of the coils, giving necessary clearances for insu- lation, etc. 230 MACHINE DRAWING PLATE D. ARMATURE FLANGES AND SPIDER We come logically then to the armature flanges and the spider. Difference Between Front and Back Flanges. The two flanges are quite similar in everything except as regards their mounting on the spider. The one for the back end of the armature, Fig. 2, merely slips back over the arms of the spider against a shoulder. The laminations are placed on the spider, and then the front flange, Fig. 1, must be arranged to press the laminations against the back one, and must be held solidly in place. Note that the inside diam- eter of the back flange is given in decimals to a thousandth of an inch and marked spider fit. Now note the corresponding dimen- sion on the front flange. While the dimension is an even eighteen and one-half inches it is given to three decimals, indicating that the machining must be done so that the given dimension is within one thousandth of an inch. This shows the workman at once where the fine work is to be done and, compared with other dimen- sions, shows the relative care which must be taken to make the size as shown. This drawing also shows, very clearly, how a whole piece may be covered in the drawing by showing only a part. Nothing what- ever could be added to the drawing by showing the whole of these two flanges, while more space would be required and more time would be needed to draw it. It will be noted that the sections are identified on the plans by lines drawn across them at the points where the sections are taken, these* lines being lettered, and a note added below the section giving the proper reference. Finish Notes for Shopman. Another thing should be noted as showing how the draftsman must consider the pattern maker. The pattern maker must make proper allowance for shrinkage and for machining, and wherever a part is marked "finish" by means of the usual /, he will add to the dimensions shown in making his pattern. Now note the arms of these flanges, shown in section on Figs. 1 and 2. Instead of putting the / across the surface to be finished, a note is given which tells the pattern maker that, while it is to be rough finished, no extra allowance is necessary. This simply illustrates the original point of the whole matter; the drawings are for the shopman, and every point, no matter how MACHINE DRAWING 231 small, must be covered so that there can be no doubt in his mind as to how to proceed. Armature Spider Details. Now, taking up the spider, Fig. 3, it will be seen that the outside dimensions are determined by those of the flanges. The shaft diameter must now be calculated, if not given by the designer, and we can proceed to complete this drawing. Note how the center of the spider is cored out to save metal, how fit dimensions are carefully marked in and given in decimals where close w T ork is desired. Note the keyways for laminations, front flange, and shaft, and note how the keys are called for in the table in the corner. Another point of interest is the way in which the draftsman has shown a section through one arm of the spider but has shown the other one full. By "bending" the section line A B C he has added clearness to the drawing and saved crosshatching consider- able space. As to this crosshatching, many drawing rooms save time by the method shown here. Instead of making the usual parallel lines, the space is filled in with, a pencil, giving a clouded appearance w T hen blue-printed. On the left end of the spider are shown the shoulder and tapped holes for the equalizer support. The equalizer support cannot be drawn until the equalizer rings have been laid out and the dimensions determined (See Plate E). PLATE E. EQUALIZER RINGS AND SUPPORT General Details. The equalizer rings just referred to may now be designed. First a diagram is drawn showing the general shape and the points at .which they are connected into the risers, Fig. 5. The details are next w r orked up, showing the exact form and all dimensions, Fig. 1. A note giving insulation data is added, the thickness being given as usual in mils or thousandths of an inch. Assembly Drawing. From the above an assembly is devel- oped, Fig. 6, showing the rings in place under the armature coils and supported by a ring attached to the armature spider. As in the case of the armature coils, the binding w T ires are shown and notes included giving number of turns, size of wire, stress on the bands, and tension on the wires. ■Insulate with 2 lauers of varnished cambric covered with bro linen drill. © Stress on bands - 18 IS lbs. Tension on P. B. Wire. JfO to 380 lbs. /Vote. Bars to be msu'ated with 2 lauers of 5 mil cotton tape £ach layer half lapped and varnished to 14 mils Peve. lop ed le noth app rox. 2bg +i, <£ of tfeuwau s-~ SECTION rlfl FLflTE £ 1 „ 4 i ? SOL T JTP. HEX. Ve -II X 4-16 I G 1 rin'fT. A 7 SUPPORT X ,. ASSEMBLY X - PI 11 GRAM FOR /ISSEMBL INC-PT. 1 X ' / PI AC RAM OF SUPPORT KIHS m ruitCHS r leap >a COf. TlMP I flL LLR .OS X J/!l -X Va " L a. IC-. Cofi.flN. EQUALIZER B1R. \\ E$ ^UALIZER RINGS & u it^tmi SUPPORT. •as m. C£N. M.f.C-6 -300 -6 00 -I -250 V, r uamtiKtt&gUBSSB-JteZbt £ runnel m*£u8MH--ML-MJl ■m/an *xJ.3fiU.±Q:lQ.lA naworm—ZZ-tftfezJa GENERAL ELECTRIC CO. SCHENECTUPY, IV, Y, N//SOSSO MACHINE DRAWING 233 Equalizer Ring Support. From the data already given in Fig. 6 and on Plate D, the support for the equalizer rings may now be drawn, Fig. 7. The principal dimensions are determined from the previous drawings and it only remains to work out the details, which need no explanation. PLATE F. COMMUTATOR DETAILS Commutator Drawing Requires Special Care. Now we come to the commutator, clamping rings, and spider or shell. Plate F is a splendid example of detail work where the draftsman must work out dimensions to the finest point, considering only not the foundry man, the machinist, and the assembler, but the ultimate result to be obtained and the use to which this part of the machine is to be put. Here we have a device which must consist of 216 copper bars insulated from each other, from the supporting shell, and from the clamping rings, having a given length and wearing depth and assembled in a cylinder having a diameter of about 23 inches. It is obvious that the only way these bars can be held in place is by clamping rings drawn up against beveled surfaces on the ends of the bars, with proper insulation between the indi- vidual bars and between the bars and the rings. Insulation must also be placed between the bars and the shell. Dimensions of Commutator Sections. It will be seen that the dimensions can only be expressed in decimals, if accurate re- sults are to be obtained. Note now the width of the top of each bar — .2963 inch shown in Fig. 5 — and, taking this dimension and the insulation thickness between each bar of .0382 inch, check back and find the circumferential length. Now compare this figure with the circumference of a circle whose diameter is 23 inches. It will be found that the thickness of the bars has been figured so closely that the total error in the length of the circum- ference will only be a matter of thousandths of an inch in a total length of some six feet. Such work is only possible by means of very fine gages. A reference will be found to a gage number, which means that the tool maker must make a gage accurate within one ten-thousandth of an inch, which will be used by the workman in making these bars. It should be noted that all dimensions between concentric surfaces are referred to radial or diametrical distances. This face. - 6 Holes iauallu spaced. 4 -10 Tap /^ deep 2 holes equally spaced in front end oh I, 7 PLATE F 1 0- A /6 /TSSEMBl'G PRESSURE. 49H88744C Z A PltKHG 46 SB 13 /J COMM. LEAP. 6 • i 414803 14 WASHER. 6 13 BOL T STP. HEX. HP. %Xiox/%L6. lA PUNM 4-31076 IZ W/tSHER. b STEEL II BOLT STP. HEX. HP.-IX8X5LG. 12 STEEL 10 NUT STP. HEX.-/"-S XfTH/CK 12 3 STOP 1 MOUL 0// •43/069 8 SHELL IHSULHT/ON 2 Hot/ LP £6 fgOSiO 7 CONE III MOUl/>£^ 48/068 6 SIDE INSUL /I TION m COPPER s SEGMENT i STEEL C. p/rrr. 1102743-8 4 CL ST MP R/hd. {/B/rcW i STEELC. FffTT. 1/02743-8 3 CL /f/iP KIN G CE/TOMTJ i i/nn cm r/trt. 3 Z SHELL K 1 /fSSEMBt- Y % COMMUTATOR. f^t M«EFaiv GEN.M .P. C.-6 -300-600-l-ZSOV \ P beoun tst./Ldd/M:/4--J&t [■MSHED BdU&lS/tjJAJiL-lL ■nv™ BtHM/UGJL-JA-lQlL INSPECTED J/-&-.IL. GENERAL. ELECTEE CO. •SCHE#ZC7flJ>r, N>Y. Ml 107403 MACHINE DRAWING 235 certainly shows that the draftsman understood his business. The whole construction is such that diameters or radii are the fixed dimensions, and any attempt to give these dimensions in any other way would cause the shopman to calculate the diameters with great chance for error. Complete Information for Shopman. It might be well at this point to emphasize the importance of giving information on the drawing in such a way and in such completeness that the shop man need ask no questions; in fact, modern shop practice requires that the workman work entirely from the drawing and the dimen- sions given there, and under no circumstances is it permitted the shopman to make any calculations. It should also be remembered that it costs much more to make additions to or changes on a drawing than the same work would have cost, if done when the drawing was made in the first place. And so we see that even so small a thing as one of these commutator bars is given closest attention, and each detail is worked out so that when the whole thing reaches the assembler it will be as easy to put together as if it were two pieces instead of several hundred. Assembly Drawing. This plate is another good example of how the draftsman may completely describe the whole by showing only a part. The assembled view, Fig. 1, loses nothing by showing a section of less than half the commutator; in fact, to spend time and money showing more would certainly be wasteful. The same may be said of the other parts shown on this plate. The assembly shown gives the general scheme of placing the parts of the commutator together so as to perform the proper func- tions. From this, the other details can be developed. Details of Armature Shell, First we must have a shell for supporting the bars and rings. This can be made in the form of two concentric cylinders with supporting arms between, Fig. 2. The size of the shaft has already been decided upon, so w T e can start with this dimension. It is not desirable to make this piece fit the shaft throughout its entire length since it would require a difficult job of boring in the shop and would add nothing to the finished piece. The casting is therefore cored out by the foundry man, so that there will be two bearing surfaces each 4^ inches long to be bored, but the central portion of the hub need not be finished. 236 MACHINE DRAWING This saves considerable time in the machine work. The thick- ness of the hub is only enough for mechanical strength to carry the commutator. The same is true of the arms and outer shell. In other words, as little material is used as possible to give the desired strength, with a proper factor of safety. Thus we have the arms 1 inch thick and, of course, the full length of the shell. The outer shell, having a number of holes through it for the studs for drawing up the rings, must be somewhat thicker than the hub. Also the rings must be considered and these holes spaced so that they will not come too close to the inner edge. The various holes, being rather hard to show clearly, are described in notes at one side of the drawing. These notes give size of hole, threading data when necessary, and any other information as to number, loca- tion, or depth that may be required. It should be noted that those dimensions which must be machined very closely are given, as in other plates, to three and four decimal places. The usual notes and marks as to finish and fits are included. Clamp Rings. The clamp rings, Figs. ? and 4, are fairly simple as to form, but accurate and careful work is shown in making the drawings, and the information must be quite as clear and complete as for the more complicated-looking pieces. Note how many dimensions are given and the reasons for them — for instance, the angles of the cone faces which must check with the cor- responding angle on the commutator bars, and the radius of the curve between the cone face and the vertical face which must be such as to turn the insulating cone without any tendency to break it. Since these rings are finished all over, a single note to that effect saves the time of putting the usual marks on all finished sur- faces. Surely the shopman will have little trouble in building this commutator from the drawing, with its wealth of detail information. How many dimensions could be omitted and how many lines left out and still be sure of the information being complete? Just enough is shown, just the right number of dimensions are given, to give complete instructions to the shopman at the smallest pos- sible expense. This stands for efficiency in drawing and in building from the drawings. 238 MACHINE DRAWING PLATE Q. ARMATURE SHAFT Details and Dimensions. The revolving parts have now been completed with the exception of the shaft. From the previous drawings all data is available for making the shaft drawing as shown in Plate G. The center lines of bearings, the center line of the armature, and the center line of the shaft itself will give the start- ing points. The size of the main section of the shaft and of the bearings has been determined. Note that the bearing at the coup- ling end is larger than the other one since the strains there are greater. The total length of bearing between oil deflectors is made slightly greater than the length of bearing to allow for end play of the armature when running. Oil Rings. If the shaft were extended in smooth lines toward the center, the oil would gradually creep along the shaft until it reached the spider or commutator shell where it would be thrown out into the machine. Rings are therefore formed on the shaft which will throw off the oil inside the bearing housing. These deflectors are shown on a larger scale so that the details can be given more clearly. Sections through the shaft for the purpose of showing the keyways are also given. Note how the finish is given according to whether it is for a fit with some other part or is a polished journal finish. Couplings. The coupling is also shown on this plate, since it forms a part of the shaft. The dimensions are given in decimals where they affect the other half coupling which will be furnished by the manufacturer of the prime mover to which the machine is to be coupled. The keys are called for in the title table by dimensions, no other information being necessary. It will be noted that only enough of the sections of armature spider and commutator shell are shown to give their location on the shaft and furnish needed dimensions. DETAILS OF FIELD FRAME AND COILS Having completed the revolving member, we now turn out attention to the magnet frame, fields, etc. 240 MACHINE DRAWING PLATE H. MAGNET FRAME AND BASE General Details. The details of the magnet frame are covered by Plate H. Certain dimensions here are fixed by the electrical design in order to give the proper amount of iron in the frame, the proper size field cores, and proper spacing of fields. The frame is made split horizontally at the center line, and the two parts are symmetrical, except that the lower half must have proper feet at the points where it rests on the base. Only one of the lower quarters, Figs. 1 and 2, is shown in the drawing, since this will give all necessary dimensions and instructions for the entire frame and the lower half is symmetrical about a vertical center line. Arrangements for Bolting Frame and Pole Pieces. The work on this drawing consists mostly of locating and dimensioning the parts already fixed by the designer and completing the mechanical details. There are some very interesting things to be seen in con- nection with some of these mechanical details. There is a pole on each side of the machine which must come exactly at the split, Fig. 2. The holes for the bolts which hold these pole pieces must come at a point which will clear the studs holding the two halves of the frame together. Also two of the poles come where the feet are located. It will be seen that the casting is made hollow at this point (see sketch marked Section "DD") and the bolts for these poles are put through from this space. The studs for holding the two halves of the frame together also come down into this space. A steel cover plate is provided so that the rough casting and bolt heads are covered and present a neat appearance. It will be noted that wherever a bolt head comes against the outside of the magnet frame, that place is spot faced, that is, faced off so as to give a flat bearing surface. Details of Feet. Several sections are shown through the feet so that their form is determined definitely all over. An en- larged view of the bead at the point where the two halves are joined is also shown. These sections and enlarged views help the pattern maker in laying out his pattern drawings, and are an essential part of the drawing. Details of Base. The base, Fig. 11, is a single iron casting. While this is but a single piece, a great deal of detail is shown in MACHINE DRAWING 241 order that the pattern maker and foundryman will have sufficient information. It will be noted that the casting is hollow, with sup- porting ribs at intervals to add strength and stiffness, and with bosses on the surface where the magnet frame and pedestals are supported. These latter must, of course, be carefully machined to give the frame and bearing pedestals the proper relative location. This plate also shows the shims, Fig. 12, used for adjusting the height of the magnet frame in order that the armature may be properly centered in the field. These shims are similar in every way to those used for the pole pieces, and serve a similar purpose. Note in this drawing again, we have an example of the partial picture, the base being symmetrical about the center line of the machine. PLATE I. POLE PIECES General Details. The general outlines and dimensions of the pole pieces for the fields are determined by the electrical design, but they must all be covered completely by drawings so that they can be built in the shop. The main fields have laminated pole pieces, that is, the pole piece is made up of thin sheets of steel punched out to definite form, Fig. 1, enough being assembled together to give the required thickness, Fig. 2. The commutating fields, Fig. 6, have solid pole pieces of forged steel. Plate I covers both of these pole pieces. Field Pole Pieces. The main pole pieces must be riveted together to form a solid piece, and the rivets must be spaced and placed in such a manner as to give the best mechanical construction. The pole tips must be shaded; that is, the amount of iron in the tips must be reduced for electrical reasons. Note how this is accomplished: Each lamination has one tip cut off in a definite manner. The laminations are then assembled with alternate pieces having this cut tip on opposite sides. The actual amount of iron in the tips is then reduced by one-half. The tips are also cut back slightly from a true arc, so that the gap between the pole and the armature is greater at the tip. The manner of holding the completed pole piece in place is also interesting. Each lamination has a rectangular hole near the top. When they are assembled, this forms a rectangular passage through the whole pole piece, Fig. 2. Part of the laminations -P5sr pi rl-8-Tap II // ■5" Prill pins to be staked in firmly /2t J\ W Each shim to consist of 4 sheets, 014 "thick. m /04 -si^r M+ 3— - Each shim to consist of a sheets of .0/4 stock. FLATE I 12 STUL C.R X r/N 6 STEEL SH. 7 SHIM 6 STL.ro/fCt, 6 POLE PIECE COMM UTATING U 5 RIVET t S. STP. SH. 4 SHIM i STCEL C-K 3 K£Y (, S /JSSCMBL.Y X S.COMM.SH S7JS67-I 1 PUliCHING V) POLE PIECES Tv$T»taeTm.G£N.M,p, C.- 6 -3 00 - 600-L-2SOV P \ P finished err/Id JLQ{US£fl-.iliJl traced BY.ti0d££iY:X-J£-M. INSPECTED &-J.Z-.U. GENERAL ELECTFUC CO. SCH£ft£CTAPY t 7V. Y. M 673 5 67 MACHINE DRAWING 243 also have another hole punched which cuts across the first one and runs out to the top edge so that a square hole is formed from the top into the first hole, shown by dotted line in Fig. 2. Bolts are passed through the frame into these holes and screwed into a threaded key, Fig. 3, placed in the first hole. Thus, when these bolts are tightened up, the pole pieces are drawn up against the frame solidly. In order that there may be some adjustment of the gap between the poles and the armature, shims, Fig. 4, are provided which can be slipped between the frame and the pole pieces, thus bringing the pole piece nearer the armature. These shims are provided with slots instead of holes, so that they can be slipped in after the poles are in place. The air gap can thus be adjusted when the machine is being assembled, without entirely removing the holding bolts. Commutating Pole Pieces. The pole pieces for the commu- tating fields are simpler than the main pole pieces, consisting of a rectangular block of forged steel. The corners at the armature end are slightly rounded, Fig. 6. Holes are drilled and tapped in the opposite end for the bolts which hold the pieces to the frame. Shims, Fig. 7, are provided for these pieces the same as for the main poles. Pins placed in the armature end are used for holding the field coils and spools. Dimensions in Tabular Form. It should be noted that a number of the dimensions on this drawling are given in tables in- stead of being placed on the drawing itself. The reason for this is one of economy. Any manufacturer making a number of machines of the same general type but of slightly differing characteristics finds that some parts for the machines of different rating vary only in a few dimensions. By placing these variable dimensions in a table a large number of pieces can be covered by the same picture and many drawings saved. Of course, the drawing w T ill not be to scale for more than one of these pieces, but on simple pieces this is not objectionable. The different parts can be distinguished by assigning a specific group number to those parts wanted for any particular machine. This group will be referred to in a general specification covering the machine wanted. Thus in the present machine the specification would call for pole pieces according to a group in a certain drawing. By reference to this group certain pieces n / - s W"/f J" p3 - -- J —/*J MACHINE DRAWING 245 would be called for by number; these numbers in turn being given in the dimension table, would fix the dimensions of the piece wanted. This is a method used in many drafting rooms where many similar pieces are used which can be treated in this way. PLATE J. MAIN FIELD COILS AND SPOOLS General Details. Having completed the pole pieces, the fields themselves and the spools for supporting them can now be completed. Plate J covers coils and spools for the main fields. These main fields consist of two parts — a series field consisting of a few turns of heavy copper (in this case one turn), which carries the main armature current, and a shunt field consisting of a large number of turns of small wire connected across the armature and carrying a small current. All the electrical characteristics of these coils will be given by the designer — the number of turns for each, the size of copper, and such other things as are fixed by the results to be obtained. Plan and Elevation of Coils. For the shunt field coils instruc- tions will be given to the winder by specification, since a drawing is not suitable for giving such information. As to the general arrangement of the coils and spool, however, a drawing must be made. Notice the plans and elevation of two complete adjacent poles, Figs. 2 and 3. These show the directions of the windings and the general locations of the terminals. The arrangement of the shunt field terminals is shown in the two sections through A A and BB. Series Field Coils. The series field, as stated above, must carry the full armature current. The coil, therefore, consists of a number of leaves of copper laid together in multiple and wound around the spool, shown in side and end views in Fig. 1. In order to keep the heating of this coil to a minimum without using too much material, proper provision must be made for ventilation. In this case, this is accomplished by placing wooden space blocks (indicated by small figures 6 and 7) in such a manner that the coil is divided into two parts and so that there is space for air circula- tion between the collars and the coil. The two parts of the coil are riveted together through the space blocks. Dowel pins are passed through one of the collars, through the space blocks, and into 246 MACHINE DRAWING recesses in the other collar, so that the coil is held rigidly in place. Since the coil occupies only three sides of the spool, a long wood space block, shown in Section A A, is provided to fill the fourth side. This block is held in place in the spool by wood pins the same as the dowels which hold the coil. Connections must be made to this coil by copper bars. The ends of the laminations are therefore carried past the side of the spool, Figs. 1, 2, and 3, and divided so as to form slots for taking quarter-inch copper bars. The drawing gives the number of lam- inations in each division and the thickness of each lamination, as well as the dimension of the spaces for the connection bars. Spools, The spool and flanges are next drawn. The spool proper, Fig. 14, is of sheet steel. The ends are turned over one- half inch to form supports for the flanges; the sides are lapped and riveted. These spools must be made to fit the pole pieces and must have proper dimensions to take the windings with adequate allow- ance for the flanges. Flanges. The flanges are of veneered maple, to give stiffness and prevent warping. Note that the two flanges enclosing the series coil, Figs. 15 and 16, are identical except in thickness and in the character of the holes for the dowel pins. One plan and two sections are therefore sufficient to show both of these flanges. The third flange, Figs. 17 and 18, must be different on adjacent poles because of the different location of the terminals. The difference is indicated on the plan and section, however, by showing the location of one notch by full lines and the other notch by dotted lines. This makes the specifications just as clear and saves time. Assembly of Adjacent Poles. An assembly of two adjacent poles is drawn to show the location of the flanges, Figs. 19 and 20. This is for the benefit of the assembler and is as necessary as the other views of drawings for the man who builds the parts. PLATE K. COMMUTATINQ FIELD COILS AND SPOOLS The commutating fields are connected in series with the arma- ture and carry the full machine current. They are therefore made of heavy copper somewhat like the series section of the main field. Plate K shows these field coils and the spool. 248 MACHINE DRAWING Commutating Coil. The coil is made up of several turns of copper each made up of twenty-two laminations of thin copper strip five-eighths of an inch wide and seventy-five-thousandths of an inch thick, Fig. 13. The coil is insulated by separating the turns with separating strips of veneered maple, shown in the side view, Fig. 1. This veneering, being thin pieces of wood glued together with alternate pieces having the grain at right angles, makes a very stiff firm support, which will not warp or twist out of shape when heated. Placing the coils in this way, they are open to air circulation all over and are easily kept cool. The ends of the coil must be supported firmly from the spool. This is accomplished by means of the two copper clips. Notice Section A A, which shows how the coil, clip, and insulation are assembled with relation to each other. Notice also how the ends of the coils are spread to form slots for the connection bars (see left-hand view Fig. 13). Spool. The spool, Figs. 2 and 3, is similar to that for the main field. The body consists of sheet steel bent to fit the pole piece and having the ends turned down to hold the collars, and the whole held in place by means of rivets in one side. The collars are of veneered maple and are drilled for dowel pins which hold the sepa- rating strips. The separating strips, Fig. 4, are also of veneered maple and are very carefully dimensioned to fit the coil. The slots must have the proper slope and each of the strips on one side must be different. Assembly Methods Considered as Draftsman's Problem. It is possible that one might go over this whole plate without giving a thought to the assembly of the coils. For example, on first thought it might seem proper to wind the coil on the assembled spool. A little thought will show, however, that this would not give a good smooth piece of work and would hardly be satisfactory. It is almost universally true that coils for electrical machinery are wound on forms and assembled afterward. By studying the construction as given in this plate, it will be seen how easy it is to take such a form-wound coil, set the separating strips into place, and slip this down over the spool body which already has one collar in place. The other collar can be placed in position and the ends of the spool body bent down over the top collar. It is true that this work has nothing to do with shop practice, MACHINE DRAWING 249 and yet the draftsman must sooner or later attain a position where he sees things from the shopman's viewpoint. The above para- graph illustrates how well the draftsman realized the method to be pursued in assembling these coils. The spool might easily have been drawn so that the labor necessary to assemble it with the coil would have been double that necessary as it is drawn. As an example of what this means, the following is typical: In a certain shop, two similar electrical devices were being made, one for much heavier service than the other. An investigation of costs revealed the fact that the smaller one was costing twice as much as the larger one. Further investigation in the drafting room showed that the whole trouble was that the designing draftsman had laid out the smaller device so that the principal casting was very hard to mold in the foundry and harder still to finish in the machine shop. Simple changes in the drawing by a man familiar with shop methods made the costs of the two pieces comparable. So it will be seen that the draftsman must consider not only the pattern maker, but the foundryman, the machinist, and the assembler as well. DETAILS OF BRUSH RIGGING PLATE L. BRUSH HOLDER, STUD AND CONNECTIONS The previous plates have covered all the principal parts of the machine except the parts for collecting the current from the commutator. Plate L now takes up the details of the brushes and the brush holders. As is usual on such machines the brushes are made of carbon, Fig. 12. The size of the brushes is deter- mined by the designer, as well as the proper number to be used. Pigtail. The brush must have a "pigtail", Fig. 11, that is, a small cable to connect to the shank of the brush holder in order to get a solid electrical contact between the two. The pigtail is in this case attached to the brush by a copper tube passed through a hole in the brush and through the terminal on the pigtail. Both ends are then spun over, so as to draw the terminal up solidly against the carbon, Fig. 12. In order that the pigtail may clear the spring which holds the brush against the commutator, the slot for it is cut out at an angle. Both sides of the brush are recessed so that the brush can be used until it has gone clear into the holder, due to wear, without interfering with the holding tube or the pigtail. MACHINE DRAWING 251 The pigtail itself is called for in the title table only, the dimensions of the terminals and over-all length being given on the drawing. Brush Holder Shank. The brush holder shank, Fig. 2, is an alloy casting. It must be carefully machined in the brush slot, on the face next the commutator and in the hole for the stud. The other surfaces are simply ground to give a smooth appearance. Note how the shank is split so that it can be clamped to the stud by means of a bolt. Tapped holes are provided for the screws which hold the pigtail and the spring holder. The thumb screw, Fig. 8, for the pigtail, not being a standard machine screw, is detailed. Spring Holder. The spring holder, Fig. 6, is a rather ingen- ious punching, only the holes for screws and pin being drilled. Note that this piece is shown in its normal shape, but that devel- opment is necessary in order that the dies for the punch press can be made. The pin, Fig. 5, and lever, Fig. 4, for the spring, Fig. 3, are very simple and do not need explanation. The above discussion of Plate L has covered the brushes and holder completely. Four of these brushes are needed for each pole of the machine, or twenty-four in all. These must be sup- ported over the commutator so as to make proper contact, and the current must be collected from each set and carried to proper terminal strips. The brush holders and the shifting device are taken up in Plate M. The eurrent-carrying parts — the studs and connecting strips — form the remainder of Plate L. Current=Carrying Parts. Stud and Insulation Washers. The dimensions of the studs, Fig. 18, can be determined from the other drawings and from the knowledge that the yoke must be supported from a groove cut into the bearing casting. This stud must be insulated entirely from the yoke. It will be seen that two shoulders are provided. A nut, Fig. 17b, will be used to draw the first shoulder up against the yoke in the slot provided. Molded insu- lation, Figs. 17a, is placed over the stud between the shoulder and yoke and between the nut and the yoke. The stud can then be rigidly supported by the yoke but thoroughly insulated from it. The other shoulder, with a proper nut, is used for connecting alternate studs electrically by means of the bus rings. 71 Pnll I PLATE M~\ 2 STEEL / ■ PO WEL EIN Ys V//T, XIYz'L dE0/t//Ll!. 4 steel 1 f- NUT STP, HEX AS '-TO / Ya "TE/riC 2 STEEL 1 J i TUU /-ok // i, IE 1 IEONCEST E/tTT l-)17(,0B 1 Z B.H. YOKE SLOWE/t HELE) 1 IRON CJIST EETT El 1 1 B.E. YOKE(UEP£ff HEtEjEfrimdfrA 2 S TEEL i 3CEEWy 2 "El/JTHEflP^IITHP.^LC 1 STEEL » REICK " 1 STEEL i ? SHAFT 2 STEEL ■> NUTS STP. HEX. W-/ITMMiTH* 2 STEEL i i GUIDE 1 ISM CES7 - ■ COLL/lE - 3 STEEL - I TEtPEE n/V E-/i iS I IECNCEST ' E/ETNP VYftEE/L ' / STEEL > WORM X E/ SEE MEL Y is 3 BRUSH SHIFTING PEVICE c% BRUSH HOLDER YOKE. fh_bt was for. GE /v, /s/, /? c. -6 -300-600 L-ZSO V, FINBHED ^AL/CLLHEa-ji-Jt TTvnrc srrM-MHY£zJI--iiJI\ GENERAL. ELECTF BRUSH HOLDER YOKE AND BRUSH SHIFTING DEVICE Brush Holder Yoke. The brush holder yoke, which is in two pieces, Figs. 11 and 12, so that it can be slipped into the slot on the bearing when the machine is being assembled, is made in the form of a thin wheel with projecting slotted lugs for carrying the studs. These pieces are made of cast iron, and sufficient details must be shown to enable the pattern maker to provide a pattern of proper section at all points. The enlarged sections at the right are for this purpose entirely. Notice on this drawing another example of a bent section line used to save drawing other views. The line BBB is used since it will then take in one of the holes in the hub and permit clearer delineation. It will be noted that there are two holes in the hubjand two in the rim which are for the brush shifting device; the details of the latter must be worked out before the proper location of the holes can be determined. Brush Shifting Device. It will be noted that the arrangement for shifting the brushes around the commutator, in order to get the proper location for good commutation, consists of a shaft, Fig. 8, having mounted at one end a worm, Fig. 2, which engages the gear or the rack, Fig. 9, mounted on the bearing housing. When the handwheel on the shaft is revolved, the worm shifts the brush holder in one direction or another, until the proper location of brushes is secured. It is necessary, of course, to place 254 MACHINE DRAWING the shaft in such position that the worm engages the rack properly, that is, so that the pitch line of the rack and worm are tangent. The holes in the brush holder yoke can be located as soon as the worm and rack have been laid out; it will be noted that four holes are provided, although only two are necessary, so that the shaft and handwheel can be assembled on either side of the commu- tator, depending upon which is more convenient for operation. Worm and Rack. The worm, detailed in Fig. 2, is a good example of the double rectangular thread. In order that the motion may not be too slow a one-inch pitch has been determined upon, but if a single thread were used with this pitch the thread would be entirely too deep; therefore, a double thread is used, which reduces the depth to a reasonable amount. If the drawing is checked carefully, it will be noted that the worm is not drawn to scale, that is, the draftsman has made the picture in the most convenient way and has used proper dimensions. The threads are not detailed, but are covered by a note, giving the number of threads and the pitch. The teeth on the rack are, of course, determined by the pitch of the worm, so that no further information is nec- essary. It will be noted that the dimensions of the rack are given in degrees, since the amount of the shift required for the brushes would be expressed in this way. Shaft. The shaft, Fig. 8, for operating the worm is, of course, simply a cylindrical bar of sufficient length to bring the handwheel, Fig. 3, to a convenient point. The only detailed dimensions nec- essary are those referring to the holes for pins at various points. For bearings for this shaft a steel casting, Fig. 6, is used, having a stud which passes through the brush holder yoke and is secured by a nut. The shaft is held in the proper position by means of the worm which is pinned to the shaft, Fig. 2, and a collar, Fig. 5, which is also pinned to the shaft and located below the upper bearing. The construction here does not require fine work since the brushes are only shifted at long intervals and easy operation or freedom from friction is not required. The cast-iron handwheel, Fig. 3, is of simple construction, with a hub which fits over the shaft and is pinned to the shaft. The whole construction is simple enough *o be easily understood, and great elaboration is not necessary for the workmen in the shop. MACHINE DRAWING 255 BEARINGS AND PEDESTALS The machine proper, as far as electrical features are concerned, is now complete, although considerable work is still necessary or the connections between the fields and to the terminal blocks at the side of the machine. There are, however, the mechanical features of the bearings and pedestals which are taken care of in the two following plates. PLATE N. SPLIT BEARINGS FOR ARMATURE SHAFT General Details. The bearings proper, Figs. 1, 2, 5, and 6, are self-aligning, that is, they are constructed so as to adjust them- selves automatically to the position of the shaft. This is accom- plished by making the bearing casting with a hub on the outside which is turned to a spherical shape. The bearing pedestal and caps are then constructed so as to fit these pieces into a correspond- ing spherical support. This makes in effect a ball-and-socket arrangement, which allows considerable adjustment in any direction, so that it is not necessary to align the two pedestals accurately, either horizontally or vertically. Oil Ring Details. The scheme for keeping oil on the bearings is one commonly used for machines of this class. The oil is con- tained in the receptacle in the pedestal. The bearings have slots cut through, which arrangement allows oil rings to rest on the top surface of the shaft, the bottom of the ring dipping into the oil in the receptacle. As the shaft revolves, the rings pick up oil and transmit it to the top of the shaft. Grooves are cut in the babbitt metal forming the bearing surface so that this oil can flow over the whole surface of the bearing. It will be necessary, of course, for the draftsman to detail all these parts and to arrange them so that they will be easily constructed in the shop and easily assembled at any time afterward. Babbitt Metal Linings. It will be noted that the bearings are lined with babbitt metal and that the two halves of the iron shell are cast with ridges so arranged that when the metal is in place it is held solidly with no chance for slipping or turning. This metal, of course, is poured into the bearing with the shaft in place. It will be seen that the openings in the top half of the bearing are so arranged that the babbitt metal can be poured in conveniently. - Liu W ! ! I ifn it — 1 l::j r r, i 1 klT-V 1 | 'hi c i i r — ii ^'^t-t ; 3 it ! ri > t — ji n ±l.~f< n H;i DEVELOPMENT OF TOP HRLF BEFORE BABBITTING. % tmm J m^k ; — f — J r=^T DEVELOPMENT OF TOP HRLF BEFORE BABBITTING IPs l'-2 HRLF SECTION HR-AH PLAN & 3 WE VIEW OF HALF SECTION BBB PL A TE A/1 ? G-e M-/6IW a SPL IT OIL KING / stfelci v riNimfl.xg-LG. / ryrrz mrc/ic k eeat?)ngIw>tt6i4 H/iLf)Ji / P/iTT ifBjmc ■r SFAKINQ ( TOP H/IL F ) 3