Use a marker to place a mark on the plastic where it needs to be cut.
Determine what type of saw you need to cut the plastic parts. Larger parts can be cut with a miter saw or a table saw, while smaller parts may need to be cut with a router or a jigsaw. Most standard woodworking tools can cut through plastic parts as long as they are fitted with a carbide-tipped blade.
Fit a carbide-tipped saw blade on the saw or router. Use a screwdriver or wrench to remove the old steel blade and replace it with a carbide-tipped blade. Carbide-tipped saw blades last longer because the tips hold the teeth edge longer than than regular steel blades.
Clamp the plastic part in place as necessary. Small plastic pieces should be clamped to a work bench or table before they are cut.
Cut the molded plastic parts on the marked line.