TURNING PLASTICS
1.
TYPES OF PLASTICS
There are two general groups of plastics. The first
includes all phenol plastics moulded under heat
and pressure. Bakelite and For mica are
examples. In the second are all catalyst setting
plastics of various bases sold under such trade
names as Lucite, Catalin, Cast Bakelite,
Marblette, Tenite and Trafford. Those in the
second group are most generally used for
craftwork. They are easy to turn, being a little
harder than wood but much softer than any of
the soft metals.
2.
MOUNTING THE WORK
The most useful mounting device is the 4-jaw
(metal lathe) chuck. When this is not available,
cylinders can be mounted on a slightly tapered
wooden mandrel. Rods can be mounted
between centres, using either the wood
mounting centres or metal mounting
arrangements. When the spur centre is used,
slots should be sawed across the work.
4.
USE OF FORMED TOOLS FOR
PRODUCTION BEADING AND SIMILAR
OPERATIONS
When a number of identical pieces are to be
3.
USE OF WOOD TURNING CHISELS
Standard wood turning chisels are excellent for
turning plastics by means of scraping methods.
The tool rest should be slightly below centre and
the chisel handle should be held a little higher
than the cutting edge to give a negative rake.
Scraping tools should be kept to a minimum. A
large contact area, such as the full edge of the
spear-point chisel, will cause chatter and
probable chipping.
Properly worked, the chip comes off in a
continuous ribbon. In cold weather, plastic may
become brittle and should be tempered in
warm water for about ten minutes before
turning.
produced, all having a distinctive surface
pattern, preformed tools will speed the work and
assure uniformity. Patterns like those illustrated
can be created by grinding thin gauge
aluminium strips. A holder, like the one shown,
can then be used to support any one of your
prepared strips and guide it against the
workpiece.
5.
TURNING BALLS
Plastic balls are rough turned in the usual manner
and then brought to perfect roundness by using
a tube tool. The tube should be slightly less in
diameter than the finished size of the ball. It can
be brass or steel, ground square across the end.
The tool is used with or without a rest, and is
worked by swinging it from side to side.
6.
POLISHING PLASTICS
Start with sanding. First use 150-grit dry paper to
remove tool marks, than finish off with 150-grit
and 400-grit papers, in succession, used wet.
Press lightly to avoid overheating and marring
the work. Buffing gives the final polish, using the
polishing compounds commonly supplied for this
purpose. Do not press too hard or hold wheel
at one spot too long, keep moving around,
otherwise the plastic might become heat
marked.
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Fig. 72
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Fig. 70
