Tc 9-524 fundamentals of machine tools

FILING AND POLISHING ON THE LATHE
Filing and polishing are performed on the lathe to remove
tool marks, reduce the dimension slightly, or improve the
finish.
Filing on the Lathe
Mill files are generally considered best for lathe filing. The
bastard cut mill type hand file is used for roughing and the
second cut mill-type hand file for the finer class of work.
Other types such as the round, half-round, and flat hand files
may also be used for finishing irregular shaped workplaces.
Never use a file without a handle.
For filing ferrous metals, the lathe spindle speed should be
four or five times greater than the rough turning speed. For
filing nonferrous metals, the lathe spindle speed should be
only two or three times greater than the roughing speed. Too
slow a speed may cause the workpiece to be filed out of
round, while too high a speed will cause the file to slide over
the workpiece, dulling the file and glazing the piece.
NOTE: 
When filing, file left-handed if at all possible to
avoid placing your arm over the revolving chuck or lathe dog.
7-61

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TC 9-524
The file is held at an angle of about 10° to the right and
moved with a slow sliding motion from left to right so that the
teeth will have a shearing action (Figure 7-100). The direction
of stroke and angle should never be the opposite, as this will
cause chatter marks on the piece. The file should be passed
slowly over the workpiece so that the piece will have made
several revolutions before the stroke is completed.
The
pressure exerted on the file with the hands should be less than
when filing at the bench. Since there are less teeth in contact
with the workpiece, the file must be cleaned frequently to
avoid scratching.
Since filing should be used for little more than to remove
tool marks from the workpiece, only 0.002 to 0.005 inch
should be left for the tiling operation.