The files used in wood-slbjd are the same as those used in metal work. The file plays, however, a much less important part in the former than in the latter. In wood-slojd it is used chiefly to smooth curved surfaces, the interior of holes and depressions, and the ends of pieces of wood, in all cases where edge-tools cannot be used advantageously.
The file consists of a piece of steel, the shape of which may vary, and on the surface of which sharp ridges have been cut with a chisel. These ridges are equidistant the one from the other, and oblique to the length of the file. They form the file-grade (Fig. 67) - the essential characteristic of the tool.
Fig. 67. File-grade. 6/1.
A single-cut file is cut in one direction only; in a double-cut file the cuts cross one another. Both cuts incline towards the point of the tool, the result of which is that the file acts chiefly when driven forward, and has little effect when drawn back. The files used in wood-slojd have usually a tapering point. All files terminate at the other end in a tang which slots into the handle.
Fig. 68. Files. 1/4. a flat file, b half-round file, c round file.
Files are called triangular, square, flat, round, half-round, etc., according to the form of the blade in cross-section. Flat round, and half-round files are most used in wood-slojd (Fig. 68). The triangular file is used for sharpening saws (Fig. 36).
The fineness of the file depends on the number of cuts per inch. They are usually classified as coarse, medium, fine, and very fine.
Medium files, about 12 inches long, are the most useful for working in wood, but coarse files, or rasps, may be used in the first stages of work.
When in use, the file is grasped by the handle by one hand, and the wrist or fingers of the other are laid on the point to produce the required pressure. The file is passed steadily and slowly backwards and forwards over the work if the surface desired is level, and with a circular motion if it is curved. Pressure is exerted only when the file is driven forward; when it is drawn back again it is allowed to glide over the surface. When the work cannot be made fast, the file must be worked with one hand; but, whenever possible, the work should be secured to the bench, that both hands may be free to direct and steady the file.
Method of using the file.
In filing resinous or unseasoned wood, the cuts of the file are apt to become clogged with sawdust. The file may be cleaned with a stiff steel brush, but the simplest method of cleaning a wood-file is to wash it in hot water. The same file should never be used for wood and metal.
Cleaning the file.