The distance between the heavy lines in Fig. 1, measured according to the scale, three quarters of an inch to one foot, will be found to be 2 feet 3 3/4 inches. This measurement may be expressed by using the signs for feet and inches, or by writing a letter on the line and referring to the margin or notes for its value. Broken lines usually terminated by arrow-heads are used to show the extent of the measurement.
In locating a circle, give the distances of its center or circumference from two known points (Fig. 2). An oblique line must have both ends determined, or one end, its length, and inclination (Fig. 2).
The drawings of any object should consist of as many parts as are necessary to show all its dimensions. Usually three are sufficient, as in Fig. 3, in which a is the elevation, b the plan, and c the end-view or side elevation, of a rectangular block.
Sections through an object are frequently shown in drawings. If it is cut across the grain, it is shaded by straight parallel oblique lines, a and b, Fig. 4, which show two views of a section through the block, Fig. 3, on the line e f. Sections with the grain are shaded by lines parallel with the grain; thus, a vertical section through the line g h of Fig. 3 would appear as at c, Fig. 4.
Generally one perspective of an object will show a sufficient number of its details to enable a workman to understand its form. From a true perspective, as the cube in Fig. 5, measures can not be easily obtained; therefore, in illustrating the following exercises, false or parallel perspective is employed.
Fig. 6 represents a cube drawn in right and left parallel perspective. It is seen that surfaces and lines parallel with the plane of the paper are drawn their full size and correct shape. The receding horizontal lines are represented by shorter lines inclined at an angle of 45°. To obtain this shortened length, the full length of the line is laid off on a vertical line drawn from the nearest end of the receding one, and from the upper end of the length thus obtained an oblique line at an angle of 30° is let fall; where it intersects the 45° line is the shortened length, as shown in Fig. 6.
Fig. 7, a, b, and c show the elevations and plan of a work-bench, drawn to a scale of 1/4" to 1"; d and e show the details of the vise, 1/2" to V. The irregular line-shading is used to represent wooden surfaces.