Things You'll Need
1/4 inch thick plywood larger than the plastic sheet
Sharp felt-tipped marker
Sharp utility knife or equivalent
Steel ruler, longer than the plastic sheet
You can easily cut thin plastic sheets less than 1/16 inch (.063) thick with a utility knife. Harder clear plastics such as polycarbonate may require multiple passes with a knife, but the result will be a clean cut finished edge with no chips or cracks. Softer colored plastic sheets often require two passes and then must be snapped on the score line. Whichever type of thin plastic sheeting you are using, ensure that the knife blade is sharp. A dull blade will not produce a clean cut in the thin plastic sheet.
Lay the piece of 1/4-inch plywood on a firm, flat surface.
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Place the thin plastic sheet on top of the plywood.
Measure along the side of the thin plastic sheet and place a mark with the felt-tipped marker at the length you need to cut the plastic sheet. Place a corresponding mark on the side parallel to the side that you marked previously.
Set the steel ruler onto the thin plastic sheet, aligning one edge with the marks you made in Step 3. Do not slide the steel ruler across the surface of the plastic sheet. This will cause scratches and scuffing on the surface, ruining the finish of the plastic sheet.
Apply pressure to the steel ruler with one hand and place the tip of the utility knife on one edge of the plastic sheet, with the blade resting against the side of the steel ruler.
Drag the utility knife along the steel ruler until you reach the opposite edge of the plastic sheet. Repeat the process until you cut through the sheet, always ensuring the steel ruler does not move and the utility knife blade stays tight to the side of the ruler.
Lift the steel ruler from the surface of the thin plastic sheet without allowing tit to slide on the surface of the plastic.
Stand the cut piece of plastic sheeting on edge, with the edge you cut in Step 6 facing up.
Place the sharp edge of the utility knife blade against the cut edge. Hold the knife perpendicular to the cut. Drag the blade along the cut edge to remove any burrs formed while cutting the plastic sheet.