—Since it would be impossible to make full-sized drawings of some objects—a house for instance—it is customary to use a scale and by means of it make a smaller drawing, which shall have all of its parts properly proportioned. For example, if a drawing has printed upon it “¹⁄₂ inch = 1 inch,” it means for every inch of the object the drawing is but one-half an inch. The scale is to be used for measuring only. There is quite a variety of scales. Whatever scale is used, the numbers placed upon the drawing must represent the size of the object and not of the drawing.
Fig. 3.
In [Fig. 3] is shown a mechanical drawing of a common wood spool. It will be seen that there are different kinds of lines. Each has its meaning, as follows:
1. Light line—For penciling and cross-hatching.
2. Full line—For visible outlines of objects and limits of parts.
3. Heavy line—For border lines.
4. Dot line—For invisible outlines of objects and limits of invisible parts. Same width as 2.
5. Dash line—For projection lines. Same width as 1.