Polishing on a lathe can be done with a strip
of abrasive cloth suitable for the material to be
polished. Cut the strip to length and grasp it
between your fingers. Hold the material across the
work, Figure 28-19. If more pressure is required,
mount the abrasive cloth on a strip of wood or a
file, Figure 28-20. Use a high spindle speed.
The finer the abrasive, the finer the resulting
finish. A few drops of machine oil on the abrasive
will improve the finish. For the final polish,
reverse the abrasive cloth so the cloth backing is
in contact with the work.
Clean the lathe thoroughly after polishing.
Any abrasive chips left from the cloth can cause
rapid wear of the machine’s moving parts.
28.5 USING A LATHE MANDREL
It is sometimes necessary to machine the
outside diameter of a part concentric with a hole
that has been previously bored or reamed. This is
a simple operation if the material can be held in
the lathe by conventional means. There are times,
however, when the part cannot be gripped satis-
factorily to permit accurate machining. In such
cases, the work is mounted on a mandrel and
turned between centers, Figure 28-21. A mandrel
is a cylindrical piece of hardened steel that has
been machined with a very slight taper.
Work is pressed on a mandrel with a
mechanical arbor press, Figure 28-22. An arbor
press is also used to remove the mandrel after
machining. The work must first be deburred and
cleaned. The work can be lubricated with a light
oil to prevent it from “freezing” on the mandrel.
The mandrel is mounted between centers
and driven by a lathe dog. Use care so the tool
does not come in contact with the mandrel
during the machining operation.
28.6 GRINDING
The tool post grinder, Figure 28-23, permits
both internal and external grinding on a lathe.
With a few simple attachments, the lathe can be
used to sharpen reamers and milling cutters,
grind shafts, and true lathe centers.
Chapter 28 Other Lathe Operations 455
Figure 28-18.
In the right-hand filing method, your left hand and
arm will be over the revolving chuck. Avoid this
method, which has the potential for injury.
Abrasive cloth should
be pulled against
rotation of work
Figure 28-19.
Polishing with abrasive cloth held in hands. Keep
hands clear of the revolving chuck or dog.
Hold abrasive cloth
on file with thumb and
finger. Apply light pressure
and move against rotation.
Figure 28-20.
More pressure can be applied if the cloth is
supported by a file or block of wood.