Page:Sheet Metal Drafting.djvu/20

6 Figure 10 illustrates the method of getting various angles by means of the triangles separately and in combination. These angles, of course, can be drawn in the opposite slant by reversing the triangles.

Always keep the working edge of the triangle toward the head of the T-square and draw from the bottom up, or away from the body.

The Pencil.—The pencil must be properly sharpened and kept sharp. Good, clean-cut lines cannot be made with a dull pencil.

A pencil sharpened in the proper way is shown in Fig. 11. The end "a" shows the chisel point which is used for drawing lines; the end "b" shows the round point used for marking off distances and for putting in dimensions, lettering, etc. About ⅜ in. of lead should be exposed in making the end "a." Then it should be sharpened flat on two sides by rubbing it on a file or piece of sandpaper.

The Scale.—A scale is used in making a drawing on an ordinary-sized sheet of paper, so that the drawing is of the same size as the object, or some number of times larger or smaller than the object.

The triangular scale illustrated in Fig. 12 has six different scales, two on each side.

The ordinary architect's triangular scale of Fig. 12 has eleven scales. On the scale of three inches equals one foot, a space that is three inches long is divided into twelve equal parts, each of which represents an inch on the reduced scale and is itself sub-divided into two, four, eight, or sixteen equal parts, corresponding to halves, quarters, eighths, or sixteenths of an inch. The other scales are constructed in the same way. A little study of the scale with the above description of its construction will make its use clear.