the surface has been filed flat. Test the flatness with a
straightedge or with prussian blue and a surface plate.
DRAWFILING.—Drawfiling produces a finer
surface finish and usually a flatter surface than
crossfiling. Small parts, as shown in view C, are best
held in a vise. Hold the file as shown in the figure;
notice that the arrow indicates that the cutting stroke is
away from you when the handle of the file is held in the
right hand. If the handle is held in the left hand, the
cutting stroke will be toward you. Lift the file away
from the surface of the work on the return stroke. When
drawfiling will no longer improve the surface texture,
wrap a piece of abrasive cloth around the file and polish
the surface as shown in figure 1-22, view A.
USE OF FILE CARD.—As you file, the teeth of
the file may "clog up" with some of the metal filings
and scratch your work. This condition is known as
PINNING. You can prevent pinning by keeping the file
teeth clean. Rubbing chalk between the teeth will help
prevent pinning, too, but the best method is to clean the
file frequently with a FILE CARD or brush. A file card
(fig. 1-23) has fine wire bristles. Brush with a pulling
motion, holding the card parallel to the rows of teeth.
Always keep the file clean, whether you're filing
mild steel or other metals. Use chalk liberally when
filing nonferrous metals.
FILING ROUND-METAL STOCK.—Figure
1-21, view D, shows that as a file is passed over the
surface of round work, its angle with the work is
changed. This results in a rocking motion of the file as it
passes over the work. This rocking motion permits all
the teeth on the file to make contact and cut as they pass
over the work's surface, thus tending to keep the file
much cleaner and thereby doing better work.
POLISHING A FLAT-METAL SURFACE.—
When polishing a flat metal surface, first draw file the
surface as shown in figure 1-21, view C. Then, when the
best possible drawfiled surface has been obtained,
proceed with abrasive cloth, often called emery cloth.
Select a grade of cloth suited to the drawfiling. If the
drawfiling was well done, only a fine cloth will be
needed to do the polishing.
1-16
Figure 1-22.—Polishing operations.
Figure 1-23.—File card/brush cleaner.
