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e,
Figure 73 "_
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.
Figure 74
POLISHING PLASTICS
Start with sanding.
• First use 150-grit dry paper to remove tool marks.
• Then finish off with 150-grit and 400-grit papers, in succes-
sion. These abrasives should be 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 the wheel at one spot too long - keep moving around -
otherwise the plastic might become heat marked.
SANDING, BUFFING AND POLISHING
USING THE LATHE TO SAND TURNINGS
• Turnings should be sanded with the lathe running in sec-
ond lowest speed.
• A large sheet of sandpaper is useful for smoothing cylinders.
• All other sanding operations are done with a narrow strip
of abrasive paper. The best finishing grit is 3/0 for soft-
wood, 4/0 for hardwoods. Worn 2/0 paper is often used,
and is the equivalent of 3/0 or 4/0 new paper.
Figure 75
The application of the sandpaper strip is shown in the illustrations.
• Care must be excercised in order to prevent dubbing the
corners of beads, shoulders, etc.
• It is good practice to finish sanding with the work in
reverse rotation. This is particularly true when sanding
basswood, white pine and mahogany. These woods are
hard to sand clean since sanding packs the surface fuzz
down to the wood.
• Sanding very lightly, and not too long, with the lathe
reversed, will lift the fibers and cut them off clean.
Figure 76
USE OF SANDING DISCS
Coves
Wood Fibers
@
Sandpaper
Fibers Lifted and Cut Off
A fully adjustable sanding table adds to the scope and conve-
nience of sanding operations.
• Sanding is always done on the down travel side of the wheel;
working on the other side would kick the work upwards.
• Either second or third speed can be used.
The sanding disc is a metal plate with a threaded shank
which fits the end of the lathe spindle.
• Abrasive paper is glued to the machined surface of the
plate by means of a quick-drying cement (not supplied).
• Abrasive discs can be purchased or cut from the standard
sizes of abrasive paper. Some discs have the adhesive
already applied to the back side.
Figure 77
USE OF SANDING DRUMS
Refer to Figure 78.
Standard sanding drums are usually rubber cylinders which
can be expanded to hold an abrasive sleeve in place. Similar
cylinders, turned on the lathe and covered with abrasive
paper, will be adequate for the job. These have the advantage
that special sizes, tapers, etc. can be made. Adhesive papers
must be glued to the cylindrical suface precisely and com-
pletely.
The drum is used mainly for sanding the edges of curved work.
• The squareness of the edge of the work can be best
retained by using a simple form of vertical fence as shown.
• The standard sanding drums are commonly made with a
threaded hole to fit the lathe drive spindel.
20
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