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Build A Hot Wire Cutter

It's easy to build and lets you cut plastic foam without mess.

By Leo Simpson

MANY PEOPLE have a need to cut expanded polystyrene foam (you probably know it as "styrofoam" or "coolite"), foam rubber (which isn’t rubber at all!) and many other soft plastic materials.

Generally they resort to using a Stanley knife, handsaw, bandsaw, jigsaw or even an electric carving knife. . . and the result is generally a lot of mess for not much cut!

The ideal way to fashion this material is with a hot-wire cutter. Actually, that’s a bit of a misnomer. It should be called a hot-wire melter because that’s what it does – but invariably they’re called hot-wire cutters so we’ll stick to that name.

Click for larger image
OK, so it's not pretty - but it works! We scrounged the baseboard from an old kitchen cupboard, the spring from an old bed, the screw eyes and hinge from the junk box... we're sure you get the picture. Here we're about to cut through this thick block of polystyrene foam in just a second or so. The result: a beautifully clean, straight cut with no mess!

The cutter will go through most types of soft plastic just like a hot knife through butter (same principle really) and the result is a very smooth cut with no debris to sweep up afterwards. You also can do the most intricate cuts which would be impossible using any other method. And the cuts can be angled.

In addition, you can also cut very thick material. Our prototype cutter would easily cut foam over 400mm thick and it’s not hard to make a much larger one if you wished.

A hot-wire cutter is made from a length of resistance wire which is held taut and heated to just below red-heat. At this temperature you can slowly feed the material through and you will get a very smooth cut.

As you can see from the photos, we made our hot-wire cutter from a variety of materials we had lying around the place. The baseboard was made from Laminex-coated chipboard left over from a kitchen installation.

The vertical element was made from a scrap of 16mm Formply while the horizontal 5/16-inch threaded rod came from a cable reel. The hinge, screw eyes, spring and other bits were also hauled out of the junk box.

The important point to note about this project is that it does not have to look good; it just has to work.

For example, we could just as easily have used some raw chipboard for the base and a piece of hardwood decking for the vertical element. Or we could have used a piece of 3mm steel strap bent at rightangles and hinged from the base to carry the vertical cutter wire.

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