Lathes Page: 32
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18-19 AIR CORPS
d. The female center is conically bored at the tip and used to sup-
port work that is pointed on the end.
e. The drill pad center is used to drill flat stock in the lathe and
is an ordinary center shank, terminating in a disk or pad, against
which the work is held by friction.
f. The crotch center is used to hold round work at right angles to
its axis, for such operations as drilling or reaming the wrist pin
hole in a piston.
g. The half center is a plain center having a portion of the 600
end cut away. It is used for completely facing the ends of work
held between centers.
19. Mandrels.-a. The purpose of the mandrel is to hold work
that has been previously bored or reamed so that its outside surface
may be machined in relation to that bore or ream.
(1) The standard mandrel (fig. 26) is generally made of tool steel,
hardened and ground on the surface that supports the work. This
surface is usually tapered 0.00S inch per foot, and the average or stand-
arcd size is near the middle of the bearing surface. This taper allows
the work to be pressed tightly upon the bearing surface or the mandrel
where it is held by friction.
FIGuE;E 26.-Solid mandrel.
(a) Mandrels that operate on lathe centers should have center holes
as large as possible to provide ample bearing surface.
(b) The mandrel should always be lubricated before work is pressed
upon it to prevent galling.
(c) The size of a mandrel is usually marked on the large end.
(2) The expansion mandrel is used to hold work that is reamed or
bored to nonstandard sizes. Figure 27 ) shows an expansion mandrel
composed of two parts, consisting of an inner arbor which has a taper
of approximately -1,, inch for each inch of length and an outer split
shell that is tapered to fit the arbor. The split shell is placed in the
work and the tapered arbor forced into the shell, causing it to expl)and
the necessary amount. Expanding-jaw mandrels are also in common
use and are similar in construction to expansion reamers. A mandrel of
this type is illustrated in figure 27 @.
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United States. Army. Air Corps. Lathes, book, November 29, 1940; Washington, D.C.. (digital.library.unt.edu/ark:/67531/metadc96655/m1/34/: accessed August 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.