This project was inspired by an article in Model Engineers' Workshop by Harold Hall. It is simply a method of heating the sheet plastic along a fairly well defined narrow line. Once heated, the plastic can be readily and reproducibly bent by hand along the heated line. The header picture shows the top surface of the bender. It consists of two pieces of 130x 300 x 15 mm white plas coated chipboard with a gap between them. In the gap is located the heating element and a power source is connected to both ends. The gap is lined with self adhesive aluminium tape to reflect the heat.
This shows the underside of the unit. The two plas coated chipboard pieces were joined with a piece of 19 x 44 mm timber slightly longer than the chipboard. Two further pieces of 19 x 44 timber were screwed to the edges so that the unit will stand level. The white plastic box is a 12 volt 60W electronic transformer, intended for low voltage halogen lighting, and the output connects to the two ends of the heating element.
The heating element is a length of curtain wire. The plastic coating was stripped off.
This shows the termination of the curtain wire. A screw ring was screwed into the curtain wire. A M5 countersunk screw passes through the ring. Two M5 nuts and a washer were added to the screw as shown here. The countersunk screw was then screwed into a bored hole in the timber. After adjusting for height the nuts were adjusted to lock the screwed ring to the screw and to timber. Both ends of the curtain wire are terminated in the same way.
The unit is very simple to operate. After switching on, the sheet of plastic to be bent is laid over the wire and positioned so that the heating wire is directly under the bend line. As the plastic warms up it becomes curved because the side closest to the heater expands more than the cool upper surface. This will lift one edge of the plastic. As the plastic gets hotter then it will soften and lift on one side of the plastic will then drop back. At this stage the plastic sheet can be removed and bent along the heated line.