Page 123 - Robot Builder's Bonanza

92 WORKING WITH PLASTIC

Score line

Figure 9-3 Cut acrylic,
Press down Press down
equal pressure equal pressure polycarbonate, or other hard plastic
by scoring a line with a sharp knife.
Then break at the line over a round
Wooden dowel wooden dowel.

1. Use a sharp utility knife and metal carpenter’s square to “score” a cutting line. By scor-
ing you’re cutting in only part of the way— making a deep scratch. If necessary, use
clamps to hold down the square. Most sheet plastic comes with a protective peel- off
plastic on both sides. Keep it on when scoring.
2. Carefully repeat the scoring from 5 to 10 times, depending on the thickness of the
plastic. The thicker the plastic, the more scoring lines you should make.
3. Place a 1/2″- or 1″-diameter dowel under the plastic so the score line is on the top of
the dowel. With your fingers or the palms of your hands, carefully push down on both
sides of the score line. If the sheet is wide, use a piece of 1- by- 2 or 2- by- 4 lumber to
exert even pressure.

G Cracks are most likely to occur on the edges, so press on the edges first, then work your way
toward the center. Don’t force the break. If you can’t get the plastic to break off cleanly, deepen
the score line with the utility knife.

CUTTING BY SAWING
Thicker sheet plastic, as well as extruded tubes, pipes, and bars, must be cut with a saw. If you
have a table saw, outfit it with a fine- tooth blade designed for nonferrous metals when cutting
acrylic or other hard plastic, a plywood- paneling blade when cutting PVC. When cutting
acrylic and other hard plastic, slow down the feed rate— the speed at which the material is
sawed in two. Forcing the plastic or using a dull blade heats the plastic, causing it to deform
and melt.
When working with a power saw, use fences or pieces of wood held in place by C- clamps
to ensure a straight cut.
You can use a handsaw to cut smaller pieces of plastic. A hacksaw (Figure 9-4) with a
medium- or fine- tooth blade (24 or 32 teeth per inch) is a good choice. You can also use a
coping saw (with a fine- tooth blade) or a razor saw. These are good choices when cutting
angles and corners as well as when doing detail work.
You can use a motorized scroll saw to cut plastic, but you must take care to ensure a
straight cut. If possible, use a piece of plywood held in place by C- clamps as a guide fence. Be
sure the material is held down firmly. Otherwise, the plastic will vibrate against the cutting
tool, making for a very rough edge and an uneven cut.

G Slow down the speed of the scroll saw to prevent the plastic from melting at the cut as the blade
gets hot. If the plastic melts back into the cut even with the saw at its slowest setting, choose a
coarser blade.

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