Fig. 2313.
[Fig. 2313] represents a template for filing out a square hole. The edges a, b are at a right angle to each other, the wire simply serving as a handle.
There are two methods of applying this template; the first is to file out two opposite surfaces of the hole to the required diameter, making them true and parallel one to the other, and to then employ the template while filing out the remaining two sides; the other is to file out one side and apply the template from that as a base for the other sides. The first is preferable because the liability to error is a minimum.
When work is to be from a template, the latter obviously becomes the original standard, and in many cases the best method of forming it so as to insure correctness and enable its proper application to the work is a matter of great consideration. The shape of the template must, of course, be marked by lines which should be as fine and as deep as possible. But it does not matter how closely the template may be filed to these lines, it will still have some error, and this can in many cases be discovered and corrected during its application to the work. In the following examples there are principles which will be found of general application:—
Fig. 2314.
