Lathes Page: 13
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To use the above speeds on the lathe, they must be transposed to
revolutions per minute of the lathe spindle by the following formula:
f. p. m.
0.2618 x work diagram =r. P. m.
d. Feed, or the distance the tool advances during each revolution,
controls to a certain extent the speed at which the metal is removed
and finish produced. For the roughing cut (fast removal of stock),
it is ordinarily advisable to use a comparatively shallow cut and a
(1) For example, in the case of a 14-inch by 6-foot lathe, using a
tool bit of the proper size and shape, a depth of cut of 1/4 inch and a
feed of 0.030 inch can be utilized for the fast removal of stock on
short work of large diameter. A depth of 0.010 inch and feed of
0.005 inch or less might be considered a finishing cut for best results,
assuming that the set-up and machining conditions are of the best.
(2) The correct depth of cut in relation to the feed depends upon
the kind, size, and type of machine tool and tool bit, as well as the
nature of the work being machined. A depth of cut of 1 inch and
feed of 0.125 inch for some classes of work on the large turning lathes
would not be excessive, while a cut of 0.125 inch and a feed of 0.004
inch might be considered heavy cutting for work of a fragile nature
on some of the smaller bench lathes.
9. Cutting lubricants.-a. The major function of a cutting oil
or compound, as applied to lathe work, is to help carry off the heat
developed in separating the chip from the work and thereby prevent
a dangerous rise in temperature through the accumulation of such
heat. Minor functions of the cutting compound are to lubricate the
chip as it slides over the tool, improve the finish of the work, guard
against rusting, and wash away the chips from the cutting area.
b. In production operations the practice is to flood the work with
the cutting lubricant in order to obtain the full benefit of its action.
In the average shop where cutting compounds are used only for fin-
ishing and the more delicate operations, it is general practice merely
to apply lubricant when actually required.
NoTE.-Lubricating oils should never be used as cutting oils nor should cutting
oils be used as bearing lubricants.
c. The most common cutting lubricants with types of metals for
which they may be used are given below:
(1) Pure lard oil is one of the most efficient cutting oils available,
but due to its cost the undiluted oil is not generally recommended.
A water emulsion, which is a good economical cutting compound for
machine work, can be made by mixing one part of lard oil with four
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/15/: accessed April 25, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.