Note this movement in [Fig. 56] where the dash shows the correct movement of the file with relation to the work. Also observe that the file cutting ridges are not straight across the file, but at an angle to the direction of the dart.
Injuring Files.—Now the frequent practice is to use the file as shown in [Fig. 57], in which case it is moved across obliquely. The result is that the angle of the file cut is so disposed that the teeth of the file do not properly aid in the cutting, but in a measure retard the operation.
File teeth are disposed at an angle for the pur[p. 60]pose of giving them a shearing cut, which is the case when the file moves across the work on a line with its body.
To use a file as shown in [Fig. 57] injures the file without giving it an opportunity to cut as fast as it would when properly used.
Drawing Back the File.—In drawing back a file it is always better to allow it to drag over the work than to raise it up. It is frequently the case that some of the material will lodge in the teeth, and the back lash will serve to clear out the grooves.
This is particularly true in filing copper, aluminum, lead, and like metals, but it is well to observe this in all cases