Mechanical Drawing Self-Taught Comprising instructions in the selection and preparation of drawing instruments, elementary instruction in practical mechanical drawing — Inside the Classic

Selecting and testing drawing instruments 22

Testing and selecting India ink 30

Draftsmen's measuring rules 33

THE PREPARATION AND USE OF THE INSTRUMENTS.

Preparing the lining pen for use 34

The shapes of the lining pen points 35

Oil stoning pen points 36

Preparing the circle pen for use 38

The shape for circle pen points 38

Shaping circle pens for very small circles 39

A form of pen point recently introduced; forming the pen point 39

The method of oil-stoning circle pen points 40

The needle point and pen point 42

How to use the circle pen 43

German instrument to avoid slipping of a needle point 44

How to use the lining pen 45

Applying the ink to the bow-pen 46

Using a straight line or lining pen with a T square 47

Explanation of simple geometrical terms; radius; explanation of conventional dotted lines 48

A line at a right angle to another; a point; parallel lines 49

A line produced; a line bisected; a line bounding a circle; an arc of a circle; segments of a circle; the chord of an arc; a quadrant of a circle 50

A sector of a circle; a line tangent to a circle; a semicircle; centre of a circle; axis of a cylinder; to draw a circle that shall pass through three given points 51

To find the centre from which an arc of a circle has been struck; the degrees of a circle 52

To find the angle of one line to another 54

To find the angles of three lines one to the other 55

Acute angles and obtuse angles 57

Triangles; right angle triangle; obtuse angle triangle; equilateral triangle; isosceles triangle 58

Scalene triangle; a quadrangle; quadrilateral or tetragon 59

Rhomboid; trapezoid; trapezium 60

The construction of polygons 61

The names of regular polygons 62

The angles of regular polygons; the ellipse 63

Form of a true ellipse 69

The use of a trammel for drawing an ellipse 72

To draw a parabola mechanically 73

To draw a parabola by lines 74

To draw a heart cam 75

SHADOW LINES AND LINE-SHADING.

Section lining or cross-hatching 77

To represent cylindrical pieces one within the other; to represent a number of pieces one within the other 78

To represent pieces put together and having slots or keyways through them. 79

Effects of shading or cross-hatching 80

Lines in sectional shading or cross-hatching made to denote the material of which the piece is composed--lead, wood, steel, brass, wrought iron, cast iron 81

The shade line to indicate the shape of piece; representation of a washer 83

A key drawn with a shade line; shade line applied to a nut; a German pen regulated to draw lines of various breadths 84

Example of line-shading in perspective drawing, shown in a pipe threading stock and die 85

A cylindrical pin line-shaded; two cylindrical pieces that join each other; a lathe centre; a piece having a curved outline 86

Line-shading applied to a ball or sphere; applied to a pin in a socket shown in section 87

A piece of tube, where the thickness of the tube is shown; where the hollow or hole is seen, the piece shown in section; where the body is bell-mouthed and the hollow curve shown by shading 88

Example of line-shading to denote the relative distances of various surfaces from the eye 89

Line-shading to denote that the piece represented is of wood; shade-lines being regular or irregular 90

Examples in marking dimensions 91

THE ARRANGEMENT OF DIFFERENT VIEWS.

The different views of a mechanical drawing; elevation; plan; general view; a figure to represent a solid cylinder 94

To represent the different sides of a cube; the use of a cross to denote a square 95

A triangular piece requires two or three views 96

To represent a ring having hexagon cross section; examples; a rectangular piece in two views 98

The position of the piece when in its place determines the name of the view in the drawing 103

Best method of projecting one view from another; the two systems of different views of a piece 106

EXAMPLES IN BOLTS, NUTS AND POLYGONS.

To represent the thread of a small screw 112

A bolt with a hexagon head 113

United States standard sizes for forged or unfinished bolts and nuts 116

The basis of the Franklin Institute or United States standard for bolts and nuts; hexagonal or hexagon heads of bolts 118

Comparison of hexagon and square heads of bolts; chamfers 120

Without chamfer; best plan for view of both square and hexagon heads 123

Drawing different views of hexagon heads 125

To draw a square-headed bolt; to draw the end view of a hexagon head 125

Use of the triangle to divide circles 129

Scales giving the length of the sides of polygons 135

To find what a square body which measures one inch on each side measures across the corners; to find what diameter a cylindrical piece of wood must be turned to which is to be squared, and each side of which square must measure an inch 136

To find a radius across corners of a hexagon or a six sided figure, the length of a side being an inch 138

To pencil in a cap nut; pencilling for a link having the hubs on one side only 145

Link with hubs on both sides; pencil lines for a double eye or a knuckle joint 146

Double eye or knuckle joint with an offset; a connecting rod end 147

A rod end with a round stem 148

A bolt with a square under the head 149

Example in which the corner where the round stem meets the square under the head is sharp; a centre punch giving an example in which the flat sides gradually run out upon a circle, the edges forming curves 150

SCREW THREADS AND SPIRALS.

Screw threads for small bolts with the angles of the thread drawn in, and the method of doing this 152

A double thread; a round top and bottom thread such as the Whitworth thread; a left hand thread; to draw screw threads of a large diameter 156

Drawing the curves for screw threads 157

To draw the United States standard thread 160

To draw a square thread 162

Form of template for drawing the curves of threads 165

To show the thread depth in a top or end view of a nut; to draw a spiral spring 166

To obtain an accurate division of the lines that divide the pitch 167

EXAMPLES FOR PRACTICE.

A locomotive spring; a stuffing box and gland; working drawings of a coupling rod; dimensions and directions marked; a connecting rod drawn and put together as it would be for the lathe, vise, or erecting shop 169

Drawings for the blacksmith 172

A locomotive frame 174

Making a drawing to scale 177

A spiral wound around a cylinder whose end is cut off at an angle 178

A cylindrical body joining another at a right-angle; a Tee for example 180

Other examples of Tees 181

Example of a cylinder intersecting a cone 186

A cylindrical body whose top face if viewed from one point would appear as a straight line, or from another a circle 188

Names of the curves and lines of gear teeth 193

How to draw spur wheel teeth 194

Professor Willis' scale of tooth proportions 195

The application of the scale 197

How to find the curve for the tooth face 198

To trace hypocycloides for the flanks of teeth 200

Sectional view of a section of a wheel for showing the dimensions through the arms and hub 202

To draw an edge view of a wheel; rules for drawing the teeth of wheels; bevel gear wheels 203

The construction to find the curves 204

To draw the arcs for the teeth 205

To draw the pitch circle of the inner and small end of the pinion teeth 206

One-half of a bevel gear and an edge view projected from the same 207

A pair of bevel wheels shown in section; drawing of a part of an Ames lathe feed motion; small bevel gears 208

Example in which part of the gear is shown with teeth in, and the remainder illustrated by circles; drawings of part of the feed motion of a Niles horizontal tool work boring mill 209

Three bevel gears, one of which is line-shaded; the construction of oval gearing; Professor Rankine's process for rectifying and subdividing circular arcs 210

Various examples of laying out gear wheels 214

PLOTTING MECHANICAL MOTIONS.

To find how much motion an eccentric will give to its rod 223

To find how much a given amount of motion of a long arm will move the short arm of a lever 224

Example of the end of a lever acting directly on a shoe; a short arm having a roller acting upon a larger roller 225

A link introduced in the place of the roller to find the amount of motion of the rod; a lever actuating a plunger in a vertical line, to find how much a given amount of motion of the long arm will actuate the plunger 226

Two levers upon their axles or shafts, the arms connected by a link and one arm connected to a rod 227

A lever arm and cam in one piece on a shaft, a shoe sliding on the line, and held against the cam face by the rod, to find the position of the face of the shoe against the cam 228

To find the amount of motion imparted in a straight line to a rod, attached to an eccentric strap 229

Examples in drawing the cut off cams employed instead of eccentrics on river steamboats in the Western and Southern States. Different views of a pair of cams 232

The object of using a cam instead of an eccentric 234

Method of drawing or marking out a full stroke cam 237

Illustration of the lines embracing cut off cams of varying limits of cut-off 240

Part played by the stroke of the engine in determining the conformation of cut-off cams; manner of finding essential points of drawings of cutoff cams 241

A cam designed to cut off the steam at five-eighths of the piston stroke 244

Three-fourths and seven-eighths cams 246

Necessary imperfections in the operations of cut-off cams 247

Drawing representing the motion which a crank imparts to a connecting rod 249

Plotting out the motion of a shaper link quick return 250

Plotting out the Whitworth quick return motion employed in machines 253

Finding the curves for moulding cutters 257

EXAMPLES IN LINE-SHADING AND DRAWING FOR LINE-SHADED ENGRAVINGS.

Arrangement of idle pulleys to guide bolts from one pulley to another; representation of a cutting tool for a planing machine 264

Drawings for photo-engraving 267

Drawing for an engraver in wood; drawings for engravings by the wax process 268

Engraving made by the wax process from a print from a wood engraving; engravings of a boiler drilling machine 269

SHADING AND COLORING DRAWINGS.

Coloring the journals of shafts; simple shading; drawing cast-iron, wrought iron, steel and copper 277

Points to be observed in coloring and shading; colored drawings to be glued around their edges to the drawing board; to maintain an even shade of color; mixing colors 278

To graduate the depth of tint for a cylindrical surface 279

The size and use of brushes; light in shading; example for shading a Medart pulley 280

To show by the shading that the surfaces are highly polished; representation of an oil cup; representation of an iron planing machine 282

Example in shading of Blake's patent direct acting steam pump 284

Example of shading an independent condenser 288

EXAMPLES OF ENGINE WORK.

Drawings of an automatic high speed engine; side and end views of the engine; vertical section of the cylinder through the valve face 289

Valve motion; governor 292

Pillow box, block crank-pin, wheel and main journal 294

Side and edge view of the connecting rod 295

A two hundred horse power horizontal steam boiler for a stationary engine; cross sectional view of the boiler shell 296

Side elevation, end view of the boiler, and setting 297

Working drawings of a one hundred horse power engine; plan and side view of the bed plate, with the main bearing and guide bars; cross sections of the bed plate; side elevation of the cylinder, with end view of the same 299

Steam chest side and horizontal cross section of the cylinder; steam chest and the valves; cam wrist plate and cut-off mechanism; shaft for the cam plate; cross head; side view and section through the centre of the eccentric and strap 301

Construction of the connecting rod 303

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A Drawing Board should be of soft pine and free from knots, so that it will easily receive the pins or tacks used to fasten down the paper. Its surface should be flat and level, or a little rounding, so that the paper shall lie close to its surface, which is one of the first requisites in making a good drawing. Its edges should be straight and at a right angle one to the other, and the ends of the battens B B in Figure 1 should fall a little short of the edge A of the board, so that if the latter shrinks they will not protrude. The size of the board of course depends upon the size of the paper, hence it is best to obtain a board as small as will answer for the size of paper it is intended to use. The student will find it most convenient as well as cheapest to learn on small drawings rather than large ones, since they take less time to make, and cost less for paper; and although they require more skill to make, yet are preferable for the beginner, because he does not require to reach so far over the board, and furthermore, they teach him more quickly and effectively. He who can make a fair drawing having short lines and small curves can make a better one if it has large curves, etc., because it is easier to draw a large than a very small circle or curve. It is unnecessary to enter into a description of the various kinds of drawing boards in use, because if the student purchases one he will be duly informed of the kinds and their special features, while if he intends to make one the sketch in Figure 1 will give him all the information he requires, save that, as before noted, the wood must be soft pine, well seasoned and free from knots, while the battens B should be dovetailed in and the face of the board trued after they are glued and driven in. To true the edges square, it is best to make the two longest edges parallel and straight, and then the ends may be squared from those long edges.

Drawing squares or T squares, as they are termed, are made of wood, of hard rubber and of steel.

There are several kinds of T squares; in one the blade is solid, as it is shown in Figure 5 on page 20; in another the back of the square is pivoted, so that the blade can be set to draw lines at an angle as well as across the board, which is often very convenient, although this double back prevents the triangles, when used in some positions, from coming close enough to the left hand side of the board. In an improved form of steel square, with pivoted blade, shown in Figure 2, the back is provided with a half circle divided into the degrees of a circle, so that the blade can be set to any required degree of angle at once.

Two triangles are all that are absolutely necessary for a beginner. The first is that shown in Figure 3, which is called a triangle of 45 degrees, because its edge A is at that angle to edges B and C. That in Figure 4 is called a triangle of 60 degrees, its edge A being at 60 degrees to B, and at 30 degrees to C. The edges P and C are at a right angle or an angle of 90 degrees in both figures; hence they are in this respect alike. By means of these triangles alone, a great many straight line drawings may be made with ease without the use of a drawing square; but it is better for the beginner to use the square at first. The manner of using these triangles with the square is shown in Figure 5, in which the triangle, Figure 3, is shown in three positions marked D E F, and that shown in Figure 4 is shown in three positions, marked respectively G H and I. It is obvious, however, that by turning I over, end for end, another position is attained. The usefulness in these particular triangles is because in the various positions shown they are capable of use for drawing a very large proportion of the lines that occur in mechanical drawing. The principal requirement in their use is to hold them firmly to the square-blade without moving it, and without permitting them to move upon it. The learner will find that this is best attained by so regulating the height of the square-blade that the line to be drawn does not come down too near the bottom of the triangle or edge of the square-blade, nor too high on the triangle; that is to say, too near its uppermost point. It is the left-hand edge of the triangle that is used, whenever it can be done, to produce the required line.

To draw curves that are not formed of arcs or parts of circles, templates called curves are provided, examples of these forms being given in Figure 6. They are made in wood and in hard rubber, the latter being most durable; their uses are so obvious as to require no explanation. It may be remarked, however, that the use of curves gives excellent practice, because they must be adjusted very accurately to produce good results, and the drawing pen must be held in the same vertical plane, or the curve drawn will not be true in its outline.

It is not intended or necessary to enter into an elaborate discussion of the various kinds of drawing instruments, since the purchaser can obtain a good set of drawing instruments from a reputable dealer by paying a proportionate price, and must _per force_ learn to use such as his means enable him to purchase. It is recommended that the beginner purchase as good a set of instruments as his means will permit, and that if his means are limited he purchase less than a full set of instruments, having the same of good quality.

All the instruments that need be used in the examples of this book are as follows:

A small spring bow-pen for circles, a lining pen or pen for straight lines, a small spring bow-pencil for circles, a large bow-pen with a removable leg to replace by a divider leg or a pencil leg, and having an extension piece to increase its capacity.

The spring bow-pen should have a stiff spring, and should be opened out to its full capacity to see that the spring acts well when so opened out, keeping the legs stiff when opened for the larger diameters. The purchaser should see that the joint for opening and closing the legs is an easy but not a loose fit on the screw, and that the legs will not move sideways. To test this latter, which is of great importance in the spring bow-pencil as well as in the pen, it is well to close the legs nearly together and taking one leg in one hand and the other leg in the other hand (between the forefinger and thumb), pushing and pulling them sideways, any motion in that direction being sufficient to condemn the instrument. It is safest and best to have the two legs of the bow-pen and pencil made from one piece of metal, and not of two separate pieces screwed together at the top, as the screw will rarely hold them firmly together. The points should be long and fine, and as round as possible. In very small instruments separate points that are fastened with a screw are objectionable, because, in very small circles, they hide the point and make it difficult to apply the instrument to the exact proper point or spot on the drawing.

The joints of the large bow or circle-pen should also be somewhat stiff, and quite free from side motion, and the extension piece should be rigidly secured when held by the screw. It is a good plan in purchasing to put in the extension piece, open the joint and the pen to their fullest, and draw a circle, moving the pen in one direction, and then redraw it, moving it in the other direction, and if one line only appears and that not thickened by the second drawing, the pen is a good one.