Fig. 231.
By progressive determination of points, lines and surfaces, even the most complicated bodies can be completely represented for their reproduction in any application to mechanical or industrial purposes.
Fig. 232.
The spur wheel shown on [page 163] is an example of projection drawing.
The wheel is illustrated in three views: [fig. 235] is a side view, or elevation; [fig. 234] is a front elevation; [fig. 233] is a section view on C D. The section is projected from the front elevation by drawing parallel lines from the points in front elevation where the lines are intersected by the center line C D, cutting the plane of view and showing the interior shape at C D.
The side elevation, [fig. 235], is projected from the front elevation, [fig. 234], by drawing parallel lines from the edges in the front view across its face.
In actual drawing practice the figures should be made about three times larger than the example, and as follows:
For the front elevation draw the center lines A B, C D, and from their point of intersection as a center, with the compasses draw the inner circle or hole, also the pitch line E E. With the dividers space this line into nineteen equal divisions; each point on this line will be the center of a tooth, and the distance from one point to the next one is the pitch of the tooth.
Now, with the dividers mark off the thickness of tooth at each side of these points on pitch line; with the compasses draw the outer circle for points of teeth, the inner circle for the root of teeth, and circles for thickness of rim and hub; also circles representing the fillets at rim and hub. For clearness and to prevent confusion these lines are shown on one-half the wheel only, terminating in center line C D; all the lines of the front elevation are now complete excepting the teeth.