[Fig. 275] shows an elevation and a vertical section of a spur wheel. From these views the various parts in spur gears can be better understood, as they are represented here in combination, and the wheel in its entirety.
AA is the horizontal center line, BB, BB the vertical center lines, II and II the pitch lines, N thickness of tooth, O space of tooth, D total depth of tooth, C breadth of face, F diameter on pitch line, P diameter over all, G diameter of hub, E diameter of hole, H depth of hole, L thickness of rim, M thickness of web.
Much has been and still is being written on gearing. No general rule is followed by the writers; the elementary principles given will enable the student to master spur gearing, and bevel and combinations of many kinds of wheels will afterwards be found easier to delineate than the numerous lines seem to indicate.
Fig. 277.
Working Drawings.
From the “plans” made in the office are produced “working drawings”—which represent in detail the work to be done to exact measurement and of material, as indicated, by the pattern-maker, the foundry, the forge, the shop, and finally, by the erector of the completed mechanism.
How to satisfactorily fulfill the directions contained in these drawings, representing only a part of the work, so that it will fit, with needed accuracy, to all other parts of the design, is the task before each separate worker.
It is by means of this division of the process of manufacture through these drawings, that scores and hundreds of men can be employed at the same time upon a single engine or machine; thus, while handwork has been superseded by machines in many quarters, the art of drawing has not been narrowed nor diminished, for no drawings or designs have yet been made by machinery, nor are they likely to be.