Lathes Page: 53
allowing the curvature of the wheel to make the required concave cut.
Figure 49 shows a correctly ground parting tool.
c. The cutting edge of the tool is set at center height with the
sides of the blade parallel to the cross slide. The side relief of the
tool should be checked after making the set-up to see that proper
cutting clearance is provided. Work to be cut should be held in a
chuck, preferably of the four-jawed type, with the point at which
the parting is to take place as close as possible to the chuck jaws.
Work that is too long to be held in this manner may be supported
by the center rest but should never be placed between centers.
d. For successful parting, the lathe spindle bearings must fit snug'-
ly and the cross slide and compound rest gibs should be taken up
fairly tight to avoid unnecessary lost motion. The cutting speed for
parting should be comparable to turning speeds, and the feed should
be sufficient to keep a thin chip coming from the work continuously.
A power feed of approximately 0.002 inch per work revolution may
be used for this operation, although it is best for the novice to use
the hand feed, thereby retaining better control of the tool in case of
emergency. If too much pressure is used on the cross feed the tool
will gouge, and when not enough pressure is applied the tool will
e. Cast iron and brass may be parted dry, but all other materials,
particularly ferrous metals, must be kept wet with cutting oil.
33. Filing and polishing.-a. The purpose of filing and polish-
ing in the lathe is to remove toolmarks, improve the finish, or slightly
reduce the dimension.
b. Mill files are generally considered best for lathe filing. The
bastard cut file is used for roughing, and the second cut mill file
for the finer class of work. Other types, such as the round, half
round, and gulleting files, may also be used for such operations as
filing radii, fillets, curves, etc.
c. The speed for filing ferrous metals should be four to five times
the rough turning speed, while for nonferrous metals it should be
only two to three times the roughing speed. If the speed is too high
the file has a tendency to slide over the work, causing it to dull
rapidly and glaze the work. If the speed is too slow, the work may
be filed out-of-round.
d. In lathe filing, the file should be passed slowly over the revolv-
ing work so that the work will have made several revolutions before
the stroke has been completed. 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 more of a shearing action. The
motion of stroke and file angle should never be the opposite, as this
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/55/ocr/: accessed October 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.