Shop sketching

Preface

This volume presents the instruction papers prepared and used by the University Extension Division as a course for apprentices and older shop men who need a knowledge of mechanical drawing. The method of instruction is founded on those basic laws of successful vocational instruction: that the instruction must give the man just what he is going to use in his everyday work, and that this must be given in the most direct and efficient manner with the least expenditure of his time and money.

Every good mechanic must have a knowledge of drawing for two reasons. First and most important, he must be able to read mechanical drawings ; the lines on a blueprint must not be merely so many white lines on a blue background, but they must delineate an actual object in his mind. In other words, he must be taught to visualize the object from the drawing. Second, he must be able to make such occasional sketches as the better mechanics are often called upon to make. He may be on a repair job which requires that a sketch be made of a broken part; or he may want to convey to another his ideas of a special tool or fixture or machine part. At times he may find it necessary to make a pictorial representation for the benefit of someone who can not understand a regular drawing. In making dra^\angs for any of these reasons, he would use only the simplest outfit — a pencil, a piece of plain paper (often a scrap of wrapping paper of the back of an envelope), a scale or ruler for a straight-edge, and possibly a pencil compass.

This text is not intended to make draftsmen, but to teach shop men the knowledge of drawing that they need as shop men. Ability to read drawings is developed by examples from simple and well-known objects. This is further brought out and tested by problems requiring the student to construct other views from given drawings. To do this he must be able to visualize the thing represented and at the same time he is taught to make simple sketches. Other problems give practice in sketching from actual objects.

No attempt has been made to establish a standard of conventions. Those more generally accepted are given and, while sug-

V vi PREFACE

gestions are made for the unattached student, it is expected that each shop man will use those that are accepted in his own shop. Experience has shown that mechanics frequently resort to a pictorial method of representation, especially in conveying ideas to those unfamiliar with mechanical drawings. The isometric method has therefore been introduced, believing that it is in general the simplest of the oblique methods of representation. Freehand work, while desirable, introduces an added complication to the instruction and has therefore been left until the last.

The student should not be taught to depend on the use of drawing instruments which are not available '^ on the job." The following simple outfit is suggested: A pad of large size letter paper with a hard, unruled surface; a 2-H pencil; a steel scale or a folding rule; an eraser; and a pencil compass such as the Eagle Pencil Go's. No. 569. When a student shows marked ability and interest he may be encouraged to use a regular drafting outfit and to do ink work and tracing if he desires to spend the extra time required.

The course was originally written by Mr. Woolley and was later revised by Mr. Meredith, who incorporated such additions and changes as his experience in teaching it to several classes of shop men showed to be desirable. The illustrations were drawn by Mr. Ralph W. Hills, Instructor in Mechanical Drawing in the Extension Division. Mr. Hills has also contributed mamvaluable suggestions in the development of the course.

Earle B. Norris,

Associate Professor of

Mechanical Engineering.

The University of Wisconsin Madison, Wisconsin.

October 1, 1913.

Contents

Peeface vii

CHAPTER I Principles of Mechanical Drawing

1. Projections 1

2. Relations between views . . . / 4

3. Making the drawing 5

4. Dimensioning the drawing 6

5. Order of procedure 10

6. Broken lines 13

7. The compass 20

8. Arrangement of dimensions 21

9. Finish 22

10. Drawing to scale 22

11. Finish marks 23

12. Fillets 25

13. Notes on dimensioning 26

14. Drawing from objects 28

Chapter II

15. The nominal or outside diameter 31

16. The root or effective diameter 31

17. Depth of thread 31

18. Forms of threads 31

19. The V thread 31

20. The U. S. standard thread 32

21. The square thread 32

22. The Acme thread 32

23. The worm thread (B. & S. standard) 32

24. The Whitworth thread 33

25. Pitch 33

26. Bolts 33

vii viii CONTENTS

27. Bolt heads and nuts 35

28. Thread conventions 36

29. Right-hand and left-hand threads 36

30. Tapped holes. 37

31. Other thread conventions 39

32. Method of drawing square threads 39

33. Cap screws 40

34. Machine screws 41

35. Set screws 41

36. Multiple threads , / 43

CHAPTER* III

38. The use of sections . 45

39. Half sections 46

40. Broken sections 48

41. Partial sections 50

42. Revolved sections 50

43. Shortened views • 53

44. Assembly drawings in section 56

45. Conventions for cross-hatching 58

46. Conventions for pencil work 62

Chapter IV

47. Assembly and detail sheets 63

48. Drafting-room procedure 68

Chapter V

49. Spur gears 70

50. Bevel gears 71

51. Spiral and worm gears 71

52. Pitch circles 71

53. Pitch diameter 72

54. Pitch 72

CONTENTS ix

55. Gear calculations 73

56. The addendum 74

57. The dedundum 74

58. Gear repairs 75

59. Gear drawings 75

Chapter VI

60. Pictorial drawing 79

61. Isometric axes 80

62. Circles in isometric ^ , 82

63. Oblique surfaces in isometric 83

64. Examples of isometric drawing 86

65. Isometric paper 88

66. Isometric drawing on plain paper 92

CHAPTER Vn Freehand Drawing

67. The use of sketching paper 95

68. Sketching on plain paper 97

69. Freehand isometric sketching 99

Index. 101

I viii CONTENTS

27. Bolt heads and nuts 35

28. Thread conventions 36

29. Right-hand and left-hand threads 36

30. Tapped holes. 37

31. Other thread conventions 39

32. Method of drawing square threads 39

33. Cap screws 40

34. Machine screws 41

35. Set screws 41

36. Multiple threads , . ^ 43

CHAPTER* III

38. The use of sections 45

39. Half sections 46

40. Broken sections 48

41. Partial sections 50

42. Revolved sections 50

43. Shortened views • 53

44. Assembly drawings in section 56

45. Conventions for cross-hatching 58

46. Conventions for pencil work 62

CHAPTER IV

47. Assembly and detail sheets . 63

48. Drafting-room procedure 68

CHAPTER V

49. Spur gears 70

50. Bevel gears 71

51. Spiral and worm gears 71

52. Pitch circles 71

53. Pitch diameter 72

54. Pitch 72

CONTENTS ix

55. Gear calculations" 73

56. The addendum 74

57. The dedundum 74

58. Gear repairs 75

59. Gear drawings 75

CHAPTER VI

60. Pictorial drawing 79

61. Isometric axes 80

62. Circles in isometric ^ , 82

63. Oblique surfaces in isometric 83

64. Examples of isometric drawing 86

65. Isometric paper 88

66. Isometric drawing on plain paper 92

CHAPTER VII Freehand Drawing

67. The use of sketching paper 95

68. Sketching on plain paper 97

69. Freehand isometric sketching 99

Index 101

Chapter I Prjnciplks Of Mechanical Drawing Assignment 1

1. Projections. — The principle of projections is the basis of mechanical drawing and must be thoroughly understood in order to read a mechanical drawing or to make one.

In making a mechanical drawing of any object, a draftsman deals with one face at a time, and makes separate drawings or views showing how the different sides or faces look. Thus we sometimes make as many different drawings or views of an object as the piece has different sides. Each view is made as if the

Fig. 1.

draftsman w(;re looking squarely at tlic particular side he is drawing. In Fig. 1 is shown a picture of an oilstone, such as might be made by an artist or a photographer. Looking toward the corner, as in this figure, we see three faces, the side A, the end C, and the top B. Fig. 2 shows a mechanical drawing of this same oilstone. Notice that the stone has its three different faces shown by the three views A, B, and C. In all there are six faces but, since the two ends are alike, and likewise the two sides, and the top and bottom, it is necessary to show only the three different faces. Each view is a picture of one side as we

B

X

A

— Y

C

Fig. 2.

Fig. 3.

would see it if the stone were held squarely in front of, and on a level with the eye.

In making these views showing the different sides of any object, they should be placed in such a way as to show how they are related to each other in their position on the object. This is done by the principle of projection as follows: Referring to Fig. 2, notice that the top view B is placed directly above the side view A, so that the edges of B are on the same line as those of ^, as shown by the dotted lines. Also, end view C is directly in line with A. This is the principle of projection. In other words, the length of A is ''projected" directly upward to form the length of B and the height of A is ''projected'^ to the right to form the height of C. The dotted lines are never actually

Left End Elevattiom

Side Elevation

-W

C]

B

V^

RiQMT End Elevation

Bottom Vietw.

Ftg. 4.

drawn, but simply indicate the position of the straight edge in laying out the work.

Fig. 3 shows a picture of an anvil. Fig. 4 shows the complete mechanical drawing of this anvil with the correct names of the different possible views that might be shown. As a general rule, we follow this grouping: In the center we place the side view which shows the object set up in its natural position before the eye, and project the other views from it, placing the plan or top view above, the bottom view below, the right-end view or elevation on the right, and the left-end view on the left.

The views of an object which show it set up before the eye in its natural position are called elevations and are further designated as front, side, or end elevations. The top view, obtained by looking down upon an object is usually called the plan. The names which we give to the elevation views differ with different objects and different people. Usually we have two elevations given in a mechanical drawing, but people look at things differently and the view that some people would call a front view others might consider a side view. So we might have front and side elevations, or front and end elevations, or in the case of any object that does not have any particular face that could be called the front, we might call the elevations the end and side elevations.

Note Carefully. — We seldom need more than two or three views of a piece in order to show it. Generally a plan and side and end elevations are all that is necessary. It is only with very irregular objects like the anvil that we need as many as five views.

2. Relations Between Views.

-Fig. 5 shows a sketch in one

Tenon.

Mortise

Fig. 5.

view of two blocks of wood which are formed so that they may be j oined together with a mortise-and-tenon j oint . A mechanical drawing of the tenon is shown in Fig. 6. Three views are shown, namely, the side elevation AB, the plan CD, and the left-end view EF. The left-end view is shown rather than the right-end view because the form of the block and also of the tenon are shown in the left-end view. The surface A in the side elevation is shown in the other two views by the lines a. The surface B in the side elevation is represented by the lines h in the other two views. The student should check over the rest of the drawing with the aid of the letters so as to see just what each line in one view represents in the other views. The capital letters are used to mark the surfaces. The small letters mark the lines which in other views represent these same surfaces. These letters are shown merely by way of explanation and would not appear upon a working drawing. From this drawing it will be seen that whenever a surface lies flat and on a 'level with the, eye, it is represented by a line.

3. Making the Drawing. — In making the drawing in Fig. 6,

D

^A

J=

E

^d

A

A

B

Fig. 6.

we would draw the side elevation (view AB) first, laying off the various dimensions with the scale. Then in drawing the plan view (view CD) we would use the principle of projections to simplify the work and to locate the view properly with respect to the side elevation. The vertical (up and down) lines on the side elevation we would extend or project upward with the straight edge. These lines would then show the lengths of the horizontal (cross\vise) lines of the top view. After deciding how much space to leave between the views, we would then draw the horizontal lines of this view, spacing them properly with the aid of the rule or scale, to show the desired width of the object. The left-end view is drawn in a similar manner, by extending toward the left the horizontal lines of the side elevation and locating the vertical lines with the aid of the rule. These lines which are drawn from the side elevation in determining the other two views are called projection lines. They are usually drawn lightly so that they may be readily erased from the finished drawing. The distance to be left between the views is largely a matter of choice. The considerations which govern it will be developed later. From the preceding discussion it will be seen that the following relations exist between the different views:

The horizontal dimensions of the side elevation and of the plan or top view are equal.

The vertical dimensions of the side and end elevations are equal.

The horizontal dimensions of the end view and the vertical dimensions of the top view are equal. 4. Dimensioning the Drawing. — After the representation of the object is completed, it must be dimensioned for the guidance of the mechanics who are to have a part in its manufacture. Fig. 7 shows a shop drawing of the tenon shown in Fig. 5. It will be noticed that the extension lines and dimension lines have been added.

Dimension lines are light lines broken at the center for the insertion of the dimensions, and having arrowheads at their ends to show the distances which they measure. The arrowheads should be made very sharp. As shown in Fig. 8, they should have a sharp wedge shape with a slight curve to the sides rather than a V-shape. They should not be blocked in solidly.

Extension lines are light lines which show the points on the object between which the dimension is measured. Extension lines should be drawn up to about iV in. from the object and should project about | in. beyond the dimension lines.

Dimension lines should be spaced equally apart and equally distant from the object lines. About i\ in. is a good average for this spacing. Dimensions should be placed in one or two views when possible. Notice in Fig. 7 that all the dimensions are shown in two views. It is bad practice to repeat dimensions — that is, to put the same dimension in more than one of the views. Dimensions which are closely related should be placed near to each other, as shown by the arrangement of dimensions in the left-

|5"

I5

'8

-1^

Detail, of Tenon

FOR

Mortise and Tenom Joint.

Fig. 7.

end view of Fig. 7. The dimension 4f in. is known as the over-all dimension. It is usually given so that the workman may know the total length of material required. The over-all dimen-

AVOID

CORRECT

Fig. 8.

sion should be placed just outside the dimensions of which it is the sum, so that its dimension line will not be cut by any extension lines. Be sure that your small dimensions add up to be the same as the over-all dimension.

Dimensions are usually shown by vertical figures about | in. high. Fig. 9 shows the type of numerals generally used. The total height of fractions should equal twice the height of the whole numbers. The dividing line of a fraction should be opposite the middle of the whole number and should be on a level with

Freehand Lettering

ABCDEFGHIJKLnNOPQR5TUVWXYZ& the dimension line. The figures of the fraction should not touch the dividing line. All horizontal dimensions should read from the bottom of the sheet, and all vertical dimensions from the right-hand side of the sheet. Notice Figs. 11, 13, and 15, in this respect. In all of the dimension lines that run up and down the sheet the dimensions are placed so that they can be read from the right-hand end of the sheet.

In Fig. 10 is shown a picture of two pieces that form an end lap joint. A mechanical drawing of one of the pieces is shown in Fig. 11. Fig. 12 shows a cornerwise picture of an angle brace. Fig. 13 shows a complete shop drawing of the same angle. These drawings should be studied carefully observing the following points: .

Relative positions of the views.

Relations between lines in the different views.

Arrangement and position of dimensions.

Extension lines and arrowheads. 5. Order of Procedure.— In making a drawing, the first thing is to select the views to be shown and then plan their arrangement so that they will look well balanced on the sheet. If the left-end view is to be shown, the side elevation should be placed to the right to leave room for it; if the right-end view is shown, the side elevation should be placed to the left of the center. If rt i

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-.4" - f-t

*

Ancsle

4-REQUlRED STEEL

JOHN JONES 8-30-f9l2.

both ends are shown (which is only when they are very different) , then the side elevation would be placed about in the center. The elevations should be placed enough below the center of the space so as to leave room for the top view, if it is to be shown.

The lines of the object should then be drawn, probably constructing the front or side elevation first and then constructing the other views by the aid of projections from this view.

After the representation of the object is complete, the extension and dimension lines should be drawn, making them lighter than the object lines; next, the arrowheads should be put on; and then the dimensions should be shown in vertical numerals about high and similar in form to those shown in Fig. 9.

in.

Finally, every plate should contain a title, which should show the name of the object, the number of pieces required for the z.

s

V^

*

A— »r

Kev

I-REQUIRED MACh. STEEL

FINISH ALL OVER machine on which it goes, the material of which they are to be made, and the scale of the drawing. There should also appear, usually in one corner, the name of the draftsman and the date when the drawing was made. The plain vertical capitals shown in Fig. 9 are preferred for titles and notes as they are easily made, are very legible, and require the least practice to do a presentable job. The name of the object, being the most important part of the title, should be put in large letters, about i\ in. high. All other lettering on the plate should be about J in. high. In order to get the lettering on a straight line, very light guide lines should be drawn before beginning to letter.

As the mechanic is guided in his work by information which is given entirely on the drawings, it is, therefore, necessary that all drawings should give complete information. Besides showing the shape and size of the parts, the drawings must give full information as to the material to be used, the finish of all surfaces — whether rough, machined, tempered, hardened, etc.^ — ^the kinds and sizes of all screws, bolts, etc., and the number of pieces required.

Fig. 14 shows a sketch of a gib key. A working drawing of this key is shown in Fig. 15, with an appropriate title. Such a key is used for fastening pulleys, couplings, or collars to shafts and is driven into a slot, half of which is cut in the shaft and half in the piece to be fastened to the shaft. The head is used for pulling the key out of the slot. The slots cut in the shaft and pulleys are called ''key ways."

Fig. 16 shows the same key as was shown in Figs. 14 and 15, when viewed from a different position.

Make a working drawing of this gib key, making the views the full size of the key according to the dimensions given in Fig. 15. Draw the views of the key that would be obtained by looking along the arrows, C, D, and E, in Fig. 16. The arrangement of the views should be as shown in Fig. 17. Use the scale or rule for pointing off dimensions, and also as a straight-edge for drawing the lines. Dimension the drawing and show a complete title beneath the drawing, with your name and the date in the lower right-hand corner of the plate.

Before starting any drawing, always see that your pencil is properly sharpened to a good point. Good clean lines cannot be made with a duU pencil.

DRAW PLAN VIEW MERE

DRANA/ END VIEW HERE

6. Broken Lines. — In drawing any view, if a surface is hidden from sight but needs to be shown in some manner, it is customary to use a broken line. This hne will show the location and extent of the hidden surface, but, by being broken, will indicate that the surface represented is not on the front but is out of sight.

Broken lines are drawn with dashes about | in. long with spaces about -3V in. long between them. See Fig. 31. In drawing broken lines, they are usually made just a little lighter than the full object lines of the drawing. '

In Fig. 13, the angle was represented by solid lines throughout, because, in the views selected all the surfaces represented were visible. If, however, we wash to show the right-end view, it will appear as shown in Fig 18; the surface a is shown in the right-end view by the broken line a\ because the surface a is concealed from the eye by the upright leg of the angle. The right-end view of Fig. 11 would appear as in Fig. 19, and the right-end view of Fig. 7 would appear as in Fig. 20, for the same reasons. Hidden surfaces must always he shown by broken lines. The student should practise making broken lines so that he can space them uniformly by eye.

A judicious selection of the views to be shown will often avoid

I I I I

I I the necessity of using broken lines. For example, the left-end view of Fig. 20 shows the end outline of the tenon in full view and therefore is preferable to the right-end view. Figs. 21 and 22 show a case where the broken lines are needed. These figures show a picture and a mechanical drawing of a bronze bushing. This is a hollow cylinder, the hole extending clear through from end to end. In the side view of Fig. 22 it is necessary to represent the hole by two broken lines. These lines extend throughout the length of the side view and thus indicate that the hole extends from one end of the piece to the other. Without these it)

lines we could not tell how far the hole extended. These lines are located by projecting the top points of the inner circle of the end view.

Bronze Bushing finish all over

Suppose now that we were to make a cylinder like that of Fig. 22 but closed at one end so that it would look like a cap for a pipe. It might then be shown by the side elevation and left-end view of Fig. 23. Notice how the broken outline in the side elevation shows the form cf the interior and indicates that the hole does not extend all the way through the piece. These two views would be sufficient to give a clear idea of the cap. If the right-end view were desired, it would appear as shown at the right. The inner circle of this view is broken, because it represents a hidden surface.

Fig. 24 shows a ''stop" such as is commonly used on planer beds for bracing castings. It is shown by four views in Fig. 25. These views are not all needed but are given to show how the

1 1

J

1 1

1 \

1 / /

• r stop would appear in the different views. The right-end view contains a broken circle, because the surface which it represents is concealed when the stop is viewed from the right end. The side elevation and left-end view are all the views needed to give a complete idea of the shape of this stop.

Fig. 26 shows a sketch of a flange bushing. A complete shop drawing of this flange bushing is shown in Fig. 27. When the bushing is viewed from the left end, the 2-in. cylindrical surface is concealed from sight by the flange and is therefore shown by a broken line in the left-end view.

Always end a broken line with a dash running right up to the point where the surface ends which the line represents. Compare

— f

—

\r y

"t

* the ends of the lines in Figs. 28 and 29. Whenever a broken line crosses a full line, always make one of the dashes definitely cross the full line. The correct method of observing this is also shown in Fig. 28, and the improper method is shown in Fig. 29.

If the bushing is shown on a shaft, the diameter of which is the same as that of the hole, then the broken lines will terminate as shown in Fig. 30. This explanation applies not only to this particular problem, but to all similar cases.

I"

nOQD

CVJ

Flange Bushing 2 required brass finish all over

Fig. 27

In all work in drawing, full-line views should be shown rather than broken-line views. For instance, in drawing the cap of

Fig. 23, it is better practice to show the side elevation and left-end view rather than the side elevation and right-end view, because in the former case all of the lines of the end view are full lines while in the latter case one of the circles is broken.

7. The Compass.— Circles are drawn by means of a compass. This consists of two legs hinged at the top; one leg contains the center point while the other contains the pencil point. In order to have all lines on the drawing of uniform weight and quality, it is well for the student to break some lead from his sketching pencil and insert it in the compass. The best results will be obtained if the lead in the compass is sharpened only from the outside, either with the knife or, better, by rubbing it on a smooth file, emery cloth, or sandpaper. Do not touch the

CORRECT AND INCORRECT METHODS OF SHOWING BROKEN UNES.

CORRECT

AVOID

CORRECT inside. The point will then produce sharp lines and stand considerable usage without resharpening.

Only enough pressure should be exerted on the compass to produce distinct, clean-cut lines. Some draftsmen become quite proficient at drawing circles freehand, but a compass is always a valuable part of a sketching outfit.

It will be seen that light dot-and-dash lines are shown through the center of the views of Figs. 22, 23, 25, and 27. These are known as center lines. Whenever an object is symmetrical about a common center line (that is, just alike on both sides of the center line) it is customary to show the center line on the drawing. The most common method is to use a line made up of dashes about an inch long with dots between. Center lines should be drawn lightly. The horizontal and vertical center lines of all circular views should be shown. In starting a sketch, the center lines should always he the first lines drawn.

In making a drawing like Fig. 22, the center lines would be drawn first, and the circular end view next. The side view may then be constructed with the aid of projection lines from the end view. The object Hnes of a drawing, whether full or broken, should be be heavier than the center, extension, and dimension lines, as shown in Fig. 31 . To obtain this result, the pencil should be sharpened carefully at the beginning of the work. This will enable the student to draw fine but distinct center lines. The object should then be drawn, making the lines heavier. After completing the views, the pencil should be sharpened again preparator}^ to drawing the extension and dimension lines, which should also be fine lines.