Plastic Forming Machines
Two machines which aid the effects designer are the vacuum-forming machine and the expanded-polystyrene cutter. They are obtainable commercially, but where it would be uneconomical to buy them, they can be built cheaply and simply for short-term usage.
Expanded-polystyrene cutter
This comprises a work-top and an overhead beam which supports an electrically heated wire. Its function is to aid the cutting of small, complicated shapes in expanded-polystyrene in the same way that the fret or jigsaw cuts plywood. It also allows parallel slices or strips to be cut from block material. The work bench supports an arm to which is fastened one end of a nickel-chrome wire. The other end is fastened under the table and is spring-loaded to retain tension. The voltage is about 20–30V. The wire should reach no more than black heat as the insulation factor of the polystyrene causes a rapid temperature rise inside the material during cutting.
An adjustable guide on the bench facilitates the cutting of strips.
Vacuum-forming machine
Small items formed from lightweight, plastic sheet speed up many operations in the property-making field and the versatility of the vacuum-forming process is well appreciated in a busy effects workshop.
The device has a flat work-top under which is fitted a cylinder and a vacuum pump. The cylinder has a tap at the top which permits it, once it is partially exhausted, to suck air from the top of the bench.
The other two components are a double frame for holding the plastic sheet and an electrical heating-element.
The plastic sheet should be clamped in the frame and held down over the object to be reproduced. The heater is then lowered to a few inches from the surface and the plastic is heated until it begins to sag. At this point the heater is removed and the vacuum vessel is switched to ‘suck’. The air exhausting from the lower part of the frame draws the heated plastic down onto the master object, producing a faithful reproduction.
PLASTIC FORMING MACHINES
1. Hot-wire cutting
A table with a tensioned hot wire used to cut slices from blocks of expanded polystyrene. It may also be used to cut patterns in sheet material, a, Hot wire, b, Switch and indicator lamp, c, Low-voltage transformer, d, Tension spring.
2. Forming sheet plastic
Plastic sheet held in a rectangular clamp is heated until it becomes pliable. It is then drawn down by suction onto a master where it cools and forms a rigid copy of the original, a, Frame, b, Plastic sheet, c, Clamp, d, Vacuum control, e, Master, f, Movable heater, g, Vacuum pump, h, Vacuum cylinder.