figure 4-68. They are used to file acute internal angles,
and to clear out square corners. Certain triangular files
are used to file saw teeth.
Figure 4-68. Triangular File
Mill files. Mill files are tapered in both
width and thickness. One edge has no teeth and is
known as a safe edge. Mill files, like the one shown in
figure 4-69, are used for smoothing lathe work, draw
filing, and other precision work. They are always
Figure 4-69. Mill File
Flat files. Flat files, shown in figure 4-70,
are general-purpose files and may be either single or
double-cut. They are tapered in width and thickness.
Double-cut files are usually used for rough work, and
single-cut, smooth files are used for finish work.
Square files. Square files, shown in figure
4-71, are tapered on all four sides and are used to
enlarge rectangular holes and slots.
Round files. Round files serve the same
purpose for round openings. Atypical round file is
shown in figure 4-72. Small round files are often called
Half-round file. The half-round file is a
general purpose tool. The rounded side is used on
curved surfaces, and the flat side is used on flat
surfaces. When filing an inside curve, use a file whose
curve most nearly matches the curve of the work. This
file is shown in figure 4-73.
Figure 4-70. Flat File
Figure 4-71. Square File
Figure 4-72. Round File
Figure 4-73. Half-Round File
Curved-tooth files. Curved-tooth files are
generally used on aluminum and sheet steel and on
both flat and curved surfaces. They are also used for
smooth, rapid work on bronze, lead, babbitt, zinc and
plastic. The teeth come standard-cut and smooth-cut.
This type of file is shown in figure 4-74.
Safety. The following paragraphs discuss
several important safety considerations regarding the
use of files.