Working Drawings
And now we come to drawings of another kind and these are not intended to please the eye but to work from, hence they are called working drawings.
When most boys, and many men, want to make anything of wood or metal they get busy with their tools forthwith and whack it out willy-nilly and of course a punk job results.
Now the right way to make an article—unless you are going to crochet a sweater—is to (1) see it in your mind’s eye, (2) then draw it out on paper to scale, and (3) build it up from the plan as the picture is called. By working this way you will be able to figure out just how much material you will need for it; see exactly how the various parts fit together, and know that it will look just right when it is done.
Drawing Tools You Should Have.
—Drawing instruments, or drawing tools as they are commonly called, consist for the most part of (1) one or more pairs of dividers; (2) one or more pairs of compasses with pen and pencil points, and (3) one or more ruling pens. One of each of the above tools will be enough for you to begin with. A cheap set is shown in [Fig. 46].
Fig. 46. the drawing tools you need
Then you will need (4) a rule, or scale as it is called; (5) a protractor; (6) a T square 20 inches long; (7) a 30 degree triangle 5 inches long; (8) some drawing paper[36] not less than 10 × 12 inches; (9) a couple of medium hard (HHH) lead pencils,[37] (10) a good rubber eraser;[38] (11) a bottle of Higgins’ India ink,[39] (12) a few thumb tacks, and (13) a drawing board about 12 × 17 inches. And now let’s see what these tools and other things are for and how they are used.
[36] Get a 2-ply bristol board with a medium or smooth surface.
[37] Koh-i-noor or Venus pencils are good ones.
[38] Get Faber’s red rubber Van Dyke.
[39] This is a prepared India ink but you can make your own by rubbing up stick India ink with water.
A pair of dividers is a tool having hinged legs, the free ends of which are pointed; they are used to take, mark off and subdivide distances.
The compasses are made like the dividers, but one end has a needle point and the other is hollow so that either a pencil or a drawing pen point can be slipped into it; this tool is used to draw curves and circles, either with a pencil or in ink.
A ruling pen is formed of two bowed steel blades having a screw adjustment so that they can be forced together or drawn apart and so make lines of varying widths. Not only is a ruling pen different from a writing pen but the ink that is used with it is thicker than an ordinary writing ink. This pen is used to make straight lines by running it along the edge of a rule or T square.
A protractor is a semi-circle of brass or of German silver and it is divided into 180 degrees—since it is half of a circle and there are 360 degrees in a circle. You can buy one for a quarter.
By placing the edge of your rule in the center of the straight edge of the protractor and laying it on any one of the lines—they are numbered from 0 to 180—you will find the number of degrees the edge of the rule is from the horizontal.
Fig. 47. the t square and triangle on the drawing board
The T square is laid with the head, that is the short thick piece, against the left hand edge of the drawing board which brings the blade, that is the long thin piece flat on and across the board. The triangle is placed against the straight edge. The triangle is laid on the board with one of its edges against the blade of the T square as shown in [Fig. 47].
Simple Working Drawings.
—There are two kinds of working drawings that will be of use to you and these are, (1) plan drawings, and (2) isometric (pronounced i-so-met´-ric) drawings and you will find both of these quite easy to do.
Making Plan Drawings.
—Suppose now you want to draw the plans of a box which, let’s imagine, is to be 5 inches high, 6 inches wide and 8 inches long. The first thing to do is to draw out a view of the bottom, which also serves as the top since they are alike, and you will have a rectangle like that shown at [A in Fig. 48], and mark the dimensions on it, that is, the width and the length of the box. This you do by running a couple of arrows in each direction and marking in the size.
Fig. 48a. the plan drawings for a box
Next draw one of the sides as shown at [B] and this will give you the height and the length of the box and mark in the sizes, that is 5 and 8 inches accordingly. Finally draw the end and you will have the height and width of the box as shown at [C] and again you mark in the dimensions.
It is easy to see now that if you have all three dimensions, namely length, breadth and thickness, and that if you make a box in wood or metal it will look like the picture shown at [D] which is in isometric perspective.
Fig. 48d. the box drawn in isometric perspective
Isometric Perspective Drawings.
—The kind of perspective drawings I told you how to do under the caption of Drawing in Perspective is true perspective but engineers do drawings which they call isometric perspective, that is, while the object seems to stand out in relief there are no vanishing points.
This kind of perspective is purely mechanical and not in the least artistic but it is a great aid when you intend to make anything, for you can still draw the lines to scale and see exactly how the finished object will look.
To make a drawing of this kind draw a line on a sheet of paper near the bottom and two 30 degree lines from the ends and a vertical line through them where they meet as shown at [A in Fig. 49].
Now there are four ways by which you can get the 30 degree lines on paper and these are (1) to buy isometric ruled paper, that is paper on which the lines are already ruled; you can buy this paper for 15 cents a quire of any dealer in drawing materials or of Keuffel and Esser, 127 Fulton Street, New York City. This is the easiest and best way.
Fig. 49a. how the lines for isometric drawings are made
(2) Take a sheet of white paper exactly 5¹⁄₈ inches wide and 10 inches long and draw two diagonal lines from corner to corner so that they will cross each other, then draw a vertical line through the middle and a horizontal line near the bottom. The diagonal and horizontal lines will be 30 degrees apart.
(3) By laying a 30 degree triangle on your T square and drawing a line along the 30 degree side of it as shown in [Fig. 47]; and (4) by laying off 30 degree lines with a protractor.
To do this tack a sheet of paper on your drawing board and draw a horizontal line near the bottom of the paper with your T square; put your protractor on the horizontal line near one end, lay the edge of the rule on the center of the protractor and exactly on the 30 degree scale mark and then draw a line.
Fig. 49b. a sheet of isometric drawing paper
Slide the protractor on the opposite side of the board, draw another 30 degree diagonal line so that it will cross the first one and draw a vertical line down through the middle of the paper.
Having, now, your sheet of isometric ruled paper you are ready to do the drawing. Whatever the picture is to be, all you need to do is to follow the 30 degree lines and the vertical lines and you simply can’t help getting it in perspective.
In drawing isometric perspective circles, such as wheels, disks and the like, they are always shown as ellipses, that is, closed oblong curves. To draw an isometric ellipse,[40] make it in the proportion of ⁵⁄₈ to 1, that is, if it is ⁵⁄₈ inch wide, as we will call its minor axis, then make it 1 inch long, as we will call its major axis, as shown at [C in Fig. 49], and you will have one that is near enough the right shape for your purpose; thus if you want to show a tube or a pipe, draw it as pictured at [C]. Now with these few principles well in mind you can make a working drawing of nearly anything you please.
[40] A more complete description of isometric ellipses will be found in Inventing for Boys by the present author and published by Frederick A. Stokes Co., of New York.
Fig. 49c. the proportions of an isometric ellipse