Page:Popular Science Monthly Volume 89.djvu/488

This page needs to be proofread.

The Use of Jigs and Fixtures

��Bv S. H. Samuels

��THE average person conceives of "tools" as drills, taps, reamers, etc., but modern automatic ma- chinery has necessitated the use of jigs and fixtures for reproduction work. In

��jigs and fixtures would be unpractical and extravagant. When large quantities are to be produced and sent upon the market, however, the results are sur- prising. The cost is reduced from 50

���Fig. 3

��shop talk, they also come under the listing of tools.

Jigs and fixtures are mechanical con- trivances, such that any mechanical or electrical machine part may be placed and held rigidly, during the process of machining. Opinions vary on the exact distinction to be made between the jig and fixture.

Appliances designed for use on a drill press are called jigs, while those designed for use on other machine tools such as millers, planers, etc., are correctly called fixtures.

Jigs may be employed fur drilling, reaming, centering, tapping, etc., iiU these operations being done on the drill- press type of machine. The fixture is used in milling, turning, broaching, boring, tiuicking, planing, proliiing, cam-cutting, gear-cutting, and many other operations in nuuiiine sh<)i)s.

Jigs and fixtures have two distinct advantages— cheapness and interchange- ability of parts. When a small number of machines arc to l)e built, the use of

��Fig. 6

��to 75 per cent, due to less "tooling up" than would be necessan,- with separate parts. . .

This reduction in cost is attributed to the fact that unskilled, low-priced workmen may be empUned to operate these jigs and fixtures with the same amount of accuracy and rapidity that the well-trained, skilful machinist would do. In fact, the unskilled apprentice, with the use of jigs and fixtures, can accomplish more work, proportionately, than the high-priced machinist, who recpiires a considerable amount of time to .set up the work, measuring accurately e\ery dimension called for by the requirements. Without any doubt, jigs and fixtures eliminate brain work and consequently make machine work purely manual labor.

Since cheaji labor is used in operating them, jigs and fixtures must be made "fool-proof," thai is, they must have no comiilicattMl nu'( h.inism^ unlamihar to the I'o be well designed they must not i>e "trappy." Interchange-


�� �