Machinery Repairman

Lathe Operations
Lathe operations are about the same for plastics as
for metals. The difference is in the type of tool and
the manner in which it contacts the work. For
plastics, set the tool slightly below center. Use
cutting tools with zero or slightly negative back rake.
For both thermosettings and thermoplastics,
recommended cutting speeds are 200 to 500 fpm with
high-speed steel tools and 500 to 1,500 fpm with
carbide-tipped tools.
Finishing Operations
Plastics must be finished to remove tool marks
and produce a clean, smooth surface. Usually,
sanding and buffing are sufficient for this purpose.
3-18
You can remove surface scratches and pits by
hand sandpapering with dry sandpaper of fine grit.
You also can wet-sand by hand, with water and
abrasive paper of fine grade. If you need to remove a
large amount of material, use sanding wheels or disks.
After you have removed the pits and scratches,
buff the plastic. You can do this on a wheel made of
loose muslin buffs. Use rouge buffing compounds,
and deposit a layer of the compound on the outside of
the buffing wheel. Renew the compound frequently.
When you buff large, flat sheets, don’t use too
much pressure, and don’t hold the work too long in
one position. When buffing small plastic parts, be
careful that the wheel does not seize the piece and pull
it out of your grasp.