nd
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.

[Illustration: Fig. 150. Molding-Scrapers.]

_Scrapers_ are thin, flat pieces of steel. They may be rectangular, or
some of the edges may be curved. For scraping hollow surfaces curved
scrapers of various shapes are necessary. Convenient shapes are shown
in Fig. 150. The cutting power of scrapers depends upon the delicate
burr or feather along their edges. When properly sharpened they take
off not dust but fine shavings. Scrapers are particularly useful in
smoothing cross-grained pieces of wood, and in cleaning off glue, old
varnish, etc.

There are various devices for holding scrapers in frames or handles,
such as the scraper-plane, Fig. 111, p. 79, the veneer-scraper, and