Fig. 2318.
Fig. 2319.
Assuming, therefore, that the template a is the one to be made, we proceed to test its accuracy, bearing in mind that for this purpose the same method is to be employed whatever shape the template may be. Consequently, we make from the male template a, [Fig. 2318], a female template k, beginning at one end of k and filing it to fit a until the edges of a and k are in line when tested by a straight-edge s. We then move the template a one tooth to the right, and file another tooth in k, and proceed in this way until a number of teeth have been made, applying a square as at s, [Fig. 2319], to see that the template a is kept upright upon k. When k has been thus provided with several teeth that would fit a in any position in which the latter may be placed, we must turn template a around upon k to test the equality of the angles. Thus, suppose at the first filing the edges a, b, c, d, upon a accurately fit the template k, and the straight-edge shows the edges fair; then if we simply turn the template a around, its angles, which were before on the right, will now be on the left, as is shown at the right of [Fig. 2318]. Thus in one position a fits to e, in the other it fits to h, or b fits to f, and when turned around it fits to g, and so on. Supposing that when thus turned around the angles do not coincide, then half the error will be in the teeth of a and one-half in those of k, and the best plan will be to correct them on a to the necessary amount as near as judgment will dictate, and then to apply k as before, continuing this process until a will fit anywhere in k, and may be turned around without showing any error. But at each correction the straight-edge must be applied, and finally should be tried to prove if the teeth tops are level. We thus have two interchangeable templates, of which a may be used on the work and k kept to correct a when the latter becomes worn. It may be as well to add, however, that in first applying a to k it is best to press the straight-edge s against the edge of k, and hold it there, and then to place a against s, and slide it down into k.
Fig. 2320.
