The rasps are used principally for soft material, such as wood or for hoofs, in horse shoeing, hence they need not be considered in connection with machine-shop work.
HOLDING THE FILE.--The common mistake on the part of the beginner is to drag the file across the work at an angle. The body of the file should move across straight and not obliquely.
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.
[Illustration: _Fig. 56. Correct File Movement_]
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 purpose 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.
[Illustration: _Fig. 57. Incorrect File Movement_]
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.
The question is often asked: Where and how shall the novice commence work?
When the shop is equipped, or partially so, sufficient, at least, to turn out simple jobs, the boy will find certain tools which are strangers to him. He must become acquainted with them and not only learn their uses, but how to use them to the best advantage.
FAMILIARITY WITH TOOLS.--Familiarity with the appearance of tools, and seeing them in the hands of others will not be of any value. Nothing but the immediate contact with the tool will teach how to use it.
FILE PRACTICE.--The file is a good tool to pick up first. Select a piece of metal, six or eight inches long, and follow the instructions laid down in the chapter relating to the use of the file.