ESSENTIALS OF DRAFTING BY THE SAME AUTHOR A HANDBOOK ON PIPING 359 Pages 359 Illustrations 8 Folding Plates Postpaid, $4.00 ESSENTIALS OF DRAFTING A TEXTBOOK ON MECHANICAL DRAWING AND MACHINE DRAWING WITH CHAPTERS AND PROBLEMS ON MATERIALS STRESSES, MACHINE CONSTRUCTION AND WEIGHT ESTIMATING BY CARL L. SVENSEN, B. S. ASSISTANT PROFESSOR OF ENGINEERING DRAWING IN THE OHIO STATE UNIVERSITY, JR. MEM. A.S.M.E., MEM. S.P.E.E., FORMERLY INSTRUCTOR IN MECHANICAL ENGINEERING IN TUFTS COLLEGE AND HEAD OF THE DEPARTMEMT OF MACHINE CONSTRUCTION AT THE FRANKLIN UNION SECOND PRINTING CORRECTED NEW YORK D. VAN NOSTRAND COMPANY 25 PARK PLACE 1919 COPYRIGHT, IQl8, IQIQ. BY D. VAN NOSTRAND COMPANY THE-PLIMPTON-PKESS NOB WOOD-MA SS-U-S- A T 35} DEDICATED TO THE AUTHORS FRIEND GARDNEK. CHACE ANTHONY WHOSE INFLUENCE AS AN ENGINEER. AND TEACHER. ON THE DEVELOPMENT OF AMERJCAN MECHANICAL DRAWING IS UNIVERSALLY RECOGNIZED mmmmmmmmmmmmmmmmmmmmmmm m AOE CHAPTER XII MACHINE CONSTRUCTION 87 Machine Operations Drills The Steam Engine Pistons Sliding Bearings Wear and Pressure Stuffing Boxes Use- ful Curves and Their Application Fillets and Rounds Arcs and Straight Lines Flanged Projections Flange Edges Flanges and Bolting Keys. CHAPTER XIII SKETCHING 98 Uses of Sketching Materials for Sketching Making a Sketch Taking Measurements Some Ideas on Sketching. CHAPTER XIV ESTIMATION OP WEIGHTS 105 Accuracy Weights of Materials Weight of Loose Materials Weight of Castings Methods of Calculation Weight of Cylin- der Head Weight of Plunger Barrel Weight of Forgings. CHAPTER XV PIPING 112 Piping Materials Pipe Fittings Standard Pipe Pipe Threads. CHAPTER XVI INTERSECTIONS 117 The Line of Intersection Intersection of a Vertical Prism and a Horizontal Prism Intersection of a Vertical Prism and an Inclined Prism, Visibility of Points Intersecting Cylinders Choice of Cutting Planes Connecting Rod Intersection. CHAPTER XVII DEVELOPMENTS 123 Surfaces Development of a Prism Development of a Cylinder Development of a Pyramid The Development of a Cone De- velopment of a Transition Piece. CHAPTER XVIII PICTURE DRAWING 130 Isometric Drawing Isometric and Non-Isometric Lines Angles Positions of the Axes Construction for Circles Oblique Drawing. xiv CONTENTS PAGE CHAPTER XIX SHADE LINE DRAWINGS 136 Shade Lines System in Common Use Surface Shading Shad- ing Screw Threads and Gears Special Surface Representations Patent Office Drawing. CHAPTER XX DRAWING QUESTIONS, PROBLEMS AND STUDIES 141 INDEX... 181 ESSENTIALS OF DKAFTING CHAPTER I DRAWING INSTRUMENTS AND MATERIALS Instruments and Materials. Drawing instruments and materials should be selected with care, and under the guidance of an experienced draftsman or teacher. The really necessary equipment consists of the following: Set of case instruments comprising: 6-inch compasses with fixed needle point leg, removable pencil leg and removable pen leg, 5-inch dividers, 5-inch ruling pen, Bow pencil, bow dividers, bow pen. 24-inch T square. 16 " X 20 " drawing board. 6-inch 45 triangle. 10-inch 30 X 60 triangle. Irregular curve. 12-inch architect's scale. One dozen thumb tacks. 2 H and 4 H or 6 H drawing pencils. Drawing paper. Erasive and cleaning rubbers. Pencil pointer. Black waterproof drawing ink. Lettering pens and pen holder. Pen wiper. Use of the T Square and Triangle. The T square is used for drawing horizontal lines, with the head always against the left- hand edge of the board, Fig. 1. The upper edge of the T square blade is always used, and lines are drawn from left to right. The 1 ESSENTIALS OF DRAFTING triangles are used for drawing all other lines. Vertical lines are drawn by placing a triangle against the upper edge of the T square and drawing upward along the vertical edge, which should be placed toward the head of the T square, as shown in Fig. 2. Use of the Scale. The scale is used for laying off distances. Whenever practicable, drawings should be made full size. If a Fig. I reduced scale must be used to accommodate the size of paper, choose one which will show the object clearly, and which will not require great crowding of dimensions. For mechanical drafting, the architect's open divided scale, shown in Fig. 3, is most used. There are many forms, both flat and triangular in section. The following divisions are in general use, 1 / s , 1 /i, 3 /s, 1 /z, 3 /4> 1> iVa, and 3 inches to the foot. The scale 3 " =1' means that the drawing is one fourth the size of the object, or that each Fig. 3 one fourth inch on the drawing represents 1 inch on the object. In this case, the 3 inches is divided up into 12 parts, each of which represents 1 inch. These parts are further divided to represent quarter inches and other fractions. The double mark (") following a figure means inch or inches; the single mark (') means foot or feet. A common scale graduated to y 32 of an inch may be used for many reductions. In such cases use the half inch for an inch in drawing one half size; the quarter inch for an inch in drawing one fourth size, etc. For half size one sixteenth becomes one eighth, and similarly for other divisions. DRAWING INSTRUMENTS AND MATERIALS 3 Fig. 3 shows the distance 2 feet, &/2 inches, laid off with the scale of 3" = 1'. Drawing Pencils. It is necessary to have pencils of the right degree of hardness and properly sharpened. For lettering, Fig, 5 Fig. 6 figuring, laying out, etc., a long conical point should be used. A 2 H pencil will be found satisfactory. For the drawing itself, one 4 H pencil and one 6 H pencil, carefully sharpened, are needed. After removing the wood, Fig. 4, the lead is made slightly conical, Fig. 5, and then formed as in Fig. 6, using fine sandpaper or a file. Fig. 7 shows enlarged side and front views of the lead. Use of the Compasses. The compasses, Fig. 8, are used for drawing large circles. The needle point should be adjusted with the shoulder downward and so that the point extends about VM inch beyond the pen point, Fig. 9. A 4 H or 6 H lead should then be sharpened as for the drawing pencil, and placed in the pencil leg. Remove the pen point from the compasses, insert 4 ESSENTIALS OF DRAFTING the pencil leg, and fasten it. Then adjust the lead so that the end of it is about Vw inch above the needle point, Fig. 10. The joints in the legs are for the purpose of keeping the point and pencil perpendicular to the paper. The compasses should be operated with one hand (the right hand). The needle point should be placed in the center, and the marking point revolved clockwise. Once around is enough, starting at the point in- dicated in Fig. 11. The bow instruments are used for small circles and divisions. The method of setting the points and using is the same as for the large compasses and dividers. Use of the. Dividers. The dividers are used for transferring distances and for dividing lines. They should be handled with Full Size J Fig. 12.' Fig. 13- the right hand. When dividing a line, the points should be revolved in alternate directions, as indicated in Fig. 12. To divide a line into three parts, first set the dividers at a distance estimated to be about one third. Try it, and if too short, increase the distance between the divider points by one third of the re- maining distance. If too long, decrease the distance between the divider points by one third of the .distance which they extend beyond the end of the line. Repeat the operation if necessary. The Use of the Ruling Pen. The ruling pen is used for inking the straight lines, after the pencil drawing is finished. Ink is placed between the nibs of the pen by means of a quill which is attached to the ink bottle stopper. Care should be taken to prevent any ink from getting on the outside of the pen. The proper amount of ink is shown in Fig. 13. The pen should be held in a vertical position, and guided by the T square or triangle. It may be inclined slightly in the direction of the line which is DRAWING INSTRUMENTS AND MATERIALS 5 being drawn, but the point must always be kept from the angle formed by the paper and the guide. Do not hold the pen too tightly, or press against the guide. Both nibs of the pen must touch the paper. Frequent cleaning of the pen is necessary to obtain good lines. The same methods apply to the compass and bow pens. Character of Lines. All pencil lines should be fine, clear, and sharp. For most purposes continuous pencil lines may be used. The character and weight of ink lines for use on drawings, may be found by reference to Fig. 14. A F B G C H D J E K Fig. i '4-. A . Full line for representing visible surfaces. B. Dotted line used with A for representing invisible surfaces. Dots about Vie inch long and very close together. C. Center line very fine dot and dash. D. Witness line short dashes. E. Dimension line long dashes, or fine full line. D and E are often made the same. F. Fine line for shaded drawings. G. Dotted line for shaded drawings. H. Shade line for shaded drawings, about three times thick- ness of fine line. J. and K. for special purposes, representing conditions not specified above. When shade lines are not used, a fairly wide line should be adopted as wearing better, and giving better blueprints. The width of line will depend somewhat upon the drawing. Large simple drawings require a wide line, while small intricate draw- 6 ESSENTIALS OF DRAFTING ings necessitate narrower lines. Drawings which are large and still have considerable detail in parts require more than one width of line. An experienced draftsman will use wide lines for the large and simple parts, reducing them for the complicated places in such manner that the different widths of lines are not noticeable. The student is cautioned to proceed slowly and strive for a uniform width of line until experience teaches discre- tion. Center lines are drawn very fine, and are composed of dots and dashes. All symmetrical pieces should have a center line. All circles should have both horizontal and vertical center lines. Much information concerning the many different kinds of drawing devices used by draftsmen for saving time and other purposes can be found in the catalogues of drawing material companies. CHAPTER II LETTERING Lettering. The subject of lettering in connection with work- ing drawings is of great importance. Neat, legible letters, made free hand and with fair speed, are required. This chapter will deal with such letters. Those who wish to pursue the subject further should procure a good book on lettering, such as French & Meiklejohn's "Essentials of Lettering," published by McGraw- Hill Company, New York, or Daniels' "Freehand Lettering," published by D. C. Heath & Company, Boston, Mass. Either of these books may be obtained for $1.00. Great care and continual practice are necessary to do good lettering, but the appearance of neatness, the greater ease of reading, and lessened liability of mistakes, make up for the extra time and work. Commercial Gothic Letters. Commercial gothic and lower case letters or small letters are the forms most used by engineers and draftsmen. These are shown in Fig. 15, with the proportions and directions for drawing the various lines. The vertical capi- tals and lower case letters are shown in Fig. 16. The same pro- portions and order of strokes apply to the vertical letters. The inclined letters should have a slope of about 3 to 8, as shown in Fig. 17. Some draftsmen use the 60 slope, but this does not give as pleasing a letter (Fig. 18). In all cases very light pencil guide lines should be drawn to limit the tops and bottoms of the letters. The size of the letters is determined to some extent by the character of the work, but for most drawings the capitals should be Vs inch high, and the small letters about two thirds as high (Fig. 17). For penciling use a 2 H pencil, with a well sharpened round point. For inking, a ball point pen may be used for fairly large letters, and Gillotts 404 or 303 for small letters. The pen may be dipped into the ink and the surplus shaken back into the bottle, or the quill may be used as with the ruling pen. For good work, the pen 7 ESSENTIALS OF DRAFTING \<5\ 6 I U-5.P--J ,\\f i Vi Utf^l Q'& &' "" r ^ 3- c d ejf g h \k I m n op q r \s t u v w x = y z Fig. 15 point must be kept clean, requiring frequent wiping. The pen point should be kept pointed toward the top of the paper. Proportions and Forms. The proportions and shapes of the various letters should be studied and drawn to a large scale. For purposes of study, the letters are divided into groups. The following points should be observed. Rounded letters, such as LETTERING I LT H F E NM Z YA K V-WX O C G U "j D B P R S I 2 3 4567898 abed efghij klmnopqrs t u v w x y z Fig. 16 C, J, 0, Q, and S, may extend very slightly outside of the limiting lines. Pointed letters, like A, V, and W, may have the point extending very slightly above or below the guide lines. The horizontal bar in the letters B, E, F, H, and R is very slightly above the middle, and for the letter P it is very slightly below 10 ESSENTIALS OF DRAFTING the middle of the vertical height. For the letter A the bar is placed about one third the height of the letter. The letter W is wider than it is high. The two outside strokes of the M are parallel. Letter Spacing. The spacing between the letters when combined to form words will vary with different arrangements. The only general rule which can be given is that the area between Fig. /8 the letters should be about equal. A few illustrations will be given, showing the positions of some combinations of letters. When such letters as A and T, or A and V, are used, they should in general be placed close together, as in Fig. 19. A few words are shown in Fig. 20. In the lines marked WRONG the letters are equal distances apart. In the lines marked RIGHT the letters are spaced so that the areas between them are about equal. The AT A combination of letters in each word, or the combination of words in a line, will determine the spacing of the letters. Titles. The matter of titles for drawings is subject to great variation. The titles for detail drawings may or may not con- tain the name and location of the concern. The name of the machine, its size and number, the names of the details, scale, date, and names or initials of the draftsman and engineer, should be given. An example is shown in Fig. 21. Assembly drawings generally have more elaborate titles. Good titles cannot be made by rule, though a few suggestions may be of assistance. Jt is often advisable to center the lines composing the title. This LETTERING 11 RUN RU LAT LAT PA PA WRONG RIGHT WRONG RIGHT :R R WRONG RIGHT Fig. 20 may be done by counting from each end of each line toward the center, and placing the middle letter or space on the center line. The line can then be completed by working in opposite directions from the center line. The important facts should be given due 500 GALLON STEAM JACKETED KETTLE SCALE l^ DRAWN BY TRACED BY W. E. CHECKED BY C.S. APPROVED DATE Sept. /2. J9/7 ORDER NO. B-462 R EV I S E D Jan. Draw. No. 4-C-145 Fig. 21 12 ESSENTIALS OF DRAFTING prominence. This may be done by using large letters, by using heavier or blacker letters, by wide spacing between letters, or by using extended letters. The element of time should be con- sidered in the selection of letters. In general, the title should be placed in the lower right-hand corner of the drawing, and OHIO TECHNICAL DRAWING SCHOOL COLUMBUS. OHIO. CYLINDER FOR 4*5 VERT ENGINE Fu/1 Size Drawn by J. H Traced by J f(. - Approved by T^f"