Designing with Thermoplastics

    The thermoplastics are classified in two major categories, the Partially crystalline (polyamides, acetals, polyathenes) and Amorphous (PVC, polycarbonates, polystyrenes). The most common engineering thermoplastics are polyacetal, nylon, polyethylene, PTFE (and PEEK). They have very good machinability, excellent mechanical strength, good wear resistance, excellent sliding properties, heat and chemical resistance, and they are light-weight, and excellent electrical insulators. Plastic materials can replace metallic ones at many applications.
The most common manufacturing processes in industry for parts made by thermoplastics are:

If one refers to the industry standards he can find a lot of documentation about the thermoplastics and the above processes. But probably the most common manufacturing process is the machining (turning, milling, cutting). Small machine shops, modelers, etc. are making machinery from thermoplastic plates, rods and tubes.
The design engineer must be familiar with the thermoplastic material properties both at the machining and operating stages. Machining small size parts is the most difficult part; it requires adequate size to resist elastic deformation or break. At operation when other parts are fastened on the plastic one it is important to provide adequate contact surface. In the case of metallic with plastic part fastening due to low friction coefficient, large fastening forces are required. Instead of the large fastening forces (they will reduce the plastic part working life) the usage of dowel pins is suggested. The use of countersunk screws is preferred due to its large seating surface. In case of making a support by thermoplastic material for a shaft, make a sliding fitting and a knurling at the end of the shaft. The knurling will prevent the shaft from rotation. Otherwise (if there is enough space) use dowel pins or set screws.