It had this great advantage: It taught the workman of his day how to use the file and scraper, because both must be used conjunctively to make an absolutely flat plate.
Contrary to general beliefs, shapers and planers do not make absolutely accurate surfaces. The test of this is to put together two plates so planed off. There is just enough unevenness to permit air to get between the plates. If they were perfectly true[p. 51] they would exclude all air, and it would be a difficult matter to draw them apart.
Test of the Mechanic.—To make them perfectly flat, one plate has chalk rubbed over it, and the two plates are then rubbed together. This will quickly show where the high spots are, and the file and scraper are then used to cut away the metal.
| Fig. 46. Hexagon Nut | Fig. 47. Hexagon Nut [ToList] |
In England the test of the mechanic used to be determined by his ability to file a piece of metal flat. It was regarded as the highest art. This is not the most desirable test at the present time, and it is recognized that a much severer test is to file a narrow piece exactly flat, and so that it will not have a trace of roundness, and be square from end to end.
Test Suggestions.—In a shop which does not have the advantage of a planer or shaper, there[p. 52] are so many articles which must be filed up, that it is interesting to know something of how the various articles are made with a file.
To file a hexagon, or six-sided nut will be a good test with a file. To do this a little study in geometrical lines will save a vast amount of time. In beginning the work, measure the radius with a divider, and then step off and make six marks equidistant from each other on the round surface.
Use of the Dividers.—The distance between each of these points is equal to the radius, or half the diameter, of the round bar. See [Fig. 46], which shows this. The marks should be scribed across the surface, as shown in [Fig. 47], where the lines show the ends of the facets of the outside of the nut.