The types of plastics you find around the house include thermoset, which are rigid and retain their shape, and thermoplastics, which are pliable. Examples of thermoset plastics -- which are the more challenging of the two types to cut -- include the polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS) in your plumbing pipes, polycarbonate and acrylic sheets, and molded plastic forms. The best technique for cutting rigid plastic depends on its thickness.
Straight Cuts in Thin Sheets
The cleanest and easiest way to make straight cuts in acrylic and polycarbonate sheets that are 3/8 inches thick or less is to use a hook knife. After measuring the cut line, lay a metal straight edge along the line and clamp it securely to the bench or table. It will take more than one pass with the knife to cut through, but the first pass is the most critical. Draw the point of the blade along the straightedge, using moderate pressure, to make a score line. Pull waste material away after making this pass and each subsequent one to ensure a clean, straight edge.
Straight Cuts in Thick Sheets
You can cut through thick acrylic and polycarbonate sheets with a circular saw or a tablesaw. To minimize edge damage, use a blade designed to cut rigid plastic -- it has teeth of uniform length, and they have a uniform rake angle of 0 to 10 degrees. The blade can be steel- or carbide-tipped. Laying painter's tape along the cut line and cutting through the tape further reduces edge chipping. Clamp the sheet to a work bench for stability when using a circular saw. Use of goggles is essential, because fine plastic shards thrown out by the saw can seriously damage your eyes.
Any saw that cuts curves in wood will also cut rigid plastic, including a band saw, jigsaw, reciprocating saw or scroll saw. Fitting the saw with a metal cutting blade minimizes chipping, but it also generates heat that can melt the plastic, which may then weld together behind the saw blade. For this reason, it's advisable to ventilate the cutting area with a fan when cutting. You can cut circles in plastic by using a hole saw. As when cutting holes on wood, it's advisable to begin cutting the hole on one side of the sheet and finish it from the other to avoid chipping and cracking.
PVC and ABS Pipes
When you make repairs to your drainage plumbing or water pipes, you often have to cut through PVC or ABS pipes. Most plumbers use a hacksaw for this purpose, but you can also cut through an existing plastic drain or water pipe with a reciprocating saw. Use a dull general-purpose blade, which cuts quickly without chatter or melting. When you don't have enough room for a hacksaw or reciprocating saw, you can cut through plastic pipes with a cable saw -- an abrasive cord with handles that you can wrap around the pipe.