[Illustration: Fig. 143. Single-Cut Blunt, Flat, Bastard File.]
[Illustration: Fig. 144. Three-Square Single-Cut File.]
[Illustration: Fig. 145. Open Cut, Taper, Half-Round File.]
[Illustration: Fig. 146. Double-Cut File.]
[Illustration: Fig. 147. Cabinet Wood-Rasp.]
_Files._ Figs. 142-146, are formed with a series of cutting edges or teeth. These teeth are cut when the metal is soft and cold and then the tool is hardened. There are in use at least three thousand varieties of files, each of which is adapted to its particular purpose. Lengths are measured from point to heel exclusive of the tang. They are classified: (1) according to their outlines into blunt, (i. e., having a uniform cross section thruout), and taper; (2) according to the shape of their cross-section, into flat, square, three-square or triangular, knife, round or rat-tail, half-round, etc.; (3) according to the manner of their serrations, into single cut or "float" (having single, unbroken, parallel, chisel cuts across the surface), double-cut, (having two sets of chisel cuts crossing each other obliquely,) open cut, (having series of parallel cuts, slightly staggered,) and safe edge, (or side,) having one or more uncut surfaces; and (4) according to the fineness of the cut, as rough, bastard, second cut, smooth, and dead smooth. The "mill file," a very common form, is a flat, tapered, single-cut file.
[Illustration: Fig. 149. a. Diagram of a Rasp Tooth. b. Cross-Section of a Single-Cut File.]
_Rasps_, Fig. 147, differ from files in that instead of having cutting teeth made by lines, coarse projections are made by making indentations with a triangular point when the iron is soft. The difference between files and rasps is clearly shown in Fig. 149.
It is a good rule that files and rasps are to be used on wood only as a last resort, when no cutting tool will serve. Great care must be taken to file flat, not letting the tool rock. It is better to file only on the forward stroke, for that is the way the teeth are made to cut, and a flatter surface is more likely to be obtained.
Both files and rasps can be cleaned with a _file-card_, Fig. 148. They are sometimes sharpened with a sandblast, but ordinarily when dull are discarded.