Spotting

Hand scraped or other plane surfaces are given an attractive appearance by what is termed "spotting". A skilful worker with the hand scraper will cover a plane surface with regular spots in an artistic manner. Fig. 389 shows sections so treated. If the spots are small rectangles, the result is termed "snow flaking". Another method of handling the scraper results in small crescents or "half moons", this result is known as "frosting". In all cases where work is spotted, it results in a pleasing effect, and adds to the "classiness" of the machine or jig. The scraping pattern has also the effect of making the workman more careful of such surfaces.

Fig. 389. Typical "Spotting" Pattern on Surface Plate .Fixtures

Importance

When work-holding devices are used in machine practice they are ordinarily termed fixtures. That these are important adjuncts of the modern machine tool is made evident by a study of the various production illustrations in this book. For example, take the milling jobs shown, and it at once becomes apparent that the fixtures are a principal item in the production figures given, and so on through the whole list of production machines. Milling Fixtures. While in some cases fixtures can be used interchangeably upon planers, shapers, boring mills, and milling machines, it is more usual to find them designed for the particular machine on which they are to be used. In Fig. 390 is shown a milling machine fixture of a simple form and construction designed to hold the base of a small bench grinder, while the upper surfaces of the bearing boxes are being machined. This is done with the gang of cutters shown in the illustration. Such fixtures as this cost little and can be used by inexperienced employes. The increased

Fig. 390. Typical Milling Fixture.

Fig. 391. Typical Boring Fixture.

Fig. 392. Typical Planer Fixture, Showing Set-Up for Planing Twenty Square.

Tables at One Setting Courtesy of Worcester Polytechnic Institute Shops, Worcester, Massachusetts production alone, made possible by even so simple a fixture as the one shown, warrants its construction.