LATHE OPERATIONS - OD1645 - LESSON 1/TASK 1
(3) The bent tail clamp
lathe
dog
is
used
primarily
for
holding
rectangular workpieces.
e.
Mandrels.
(1) General. A workpiece that cannot be held between centers because its
axis has been drilled or bored, and which is not suitable for holding in a
chuck or against a faceplate, is usually machined on a mandrel. A mandrel
is a tapered axle pressed into the bore of the workpiece to support it
between centers. A mandrel should not be confused with an arbor, which is a
similar device used for holding tools rather than workpieces.
To prevent
damage to the work, the mandrel should always be oiled before being forced
into the hole. When turning work on a mandrel, feed the cutting tool toward
the large end of the mandrel, which should be nearest the headstock of the
lathe.
(2) Solid Machine Mandrel. A solid machine mandrel is generally made from
hardened steel and is ground to a slight taper ranging from 0.0005 to 0.0006
inch per inch. It has a very accurately countersunk center at each end for
mounting the workpiece between centers. The ends of the mandrel are smaller
than the body and have machined flats for the lathe dog to grip. The size
of the solid mandrel is always stamped on the large end of the taper.
(3) Expansion Mandrel. An expansion mandrel is used to hold work that is
reamed or bored to a nonstandard size. The expansion mandrel is composed of
two parts: a tapered pin that has a taper of approximately 1/16 of an inch
for each inch of length and an outer split shell that is tapered to fit the
pin.
The split shell is placed in the workpiece and the tapered pin is
forced into the shell, causing it to expand until it properly holds the
workpiece. Since solid machine mandrels have a very slight taper, they are
limited to a workpiece with specific inside diameters. An expansion mandrel
will not accept workpieces having a greater range of sizes. The expansion
mandrel is, in effect, a chuck arranged so that the grips can be forced
outward against the interior of the hole in the workpiece.
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