How to Bend and Fasten Pieces of Plastic (Published 1998) (2024)

PLASTICS can be joined with many of the same fasteners that are used to join wood and metal together. Avoid overtightening fasteners -- apply torque only until resistance is felt -- and use wide washers under bolt or screw heads and nuts to distribute the pressure beyond the fastener.

Plastics react to temperature changes more readily than metals and other materials. They can crack or break if they expand against the constraints of fasteners. Avoid this problem by making the holes in the material slightly larger than the fasteners, giving the plastic room to expand and flex with temperature changes.

Machine bolts and nuts are effective fasteners for holding two pieces of plastic together, especially if you plan to disassemble the project for any reason. Pop rivets provide a more permanent method of joining two pieces, but you need a rivet tool to install them and you cannot remove the rivets unless you drill them out.

You can also use wood screws to fasten two pieces together. The technique for driving the screws into the plastic is different from the technique for wood. First, sandwich the two pieces of thermoplastic together then drill a pilot hole. The hole should be the same length as the screw and slightly smaller than the outside diameter of the threads.

Next, grip the screw with pliers and heat it over the flame of a propane torch until it is deep blue. Push the screw directly into the pilot hole. The heat of the screw will melt the plastic and cause it to cool around the screw threads. After the screw has cooled, back it out with a screwdriver. The plastic now has a threaded hole that will accept a new screw of the same size.

You can drive machine screws into plastic, but first you must cut threads into the material. For this you need a tap the size of the fastener and a tap wrench. Drill a pilot hole in the material. The length of the hole should be equal to that of the screw. Its diameter should be slightly larger than the inside diameter of the threads. Place the tap in the wrench, lubricate it with soapy water then slowly twist it clockwise in the hole. Hold the tap wrench vertically as you cut the threads and back it out frequently to remove plastic chips. Once the threads are cut, you can drive the screw into the hole.