Thermoplastic products, and in particular parts with a foam or honeycomb inner core and a solid surface, provide weight reduction for the automotive industry. By joining such parts with lightweight metal and plastic screws and other mechanical methods, even lighter products can be manufactured. The deep axial bores required for the bearing supports of plastic conveyor pulleys should be machined for reasons of economy and dimensional accuracy. Deep holes can be successfully created in different engineering plastics with appropriate drilling parameters.