- A hot wire cutter consists of a rigid frame in a U shape, with a wire stretched across the open end of the U. The cutter should be as deep, from the wire to the flat bottom of the U, as the thickness of the foam plus a couple of inches. The cutter needs to be a couple of inches wider than the polystyrene foam to allow for ease when moving the cutter through the foam. Narrower cutters cut foam faster, so if you are cutting several different sizes and thicknesses of polystyrene foam, you should make several different sizes of hot wire cutters so that you are not using a wide cutter to make small cuts.
- You can use either PVC pipe or one-by-two-inch wood slats to build the hot wire cutter. The legs of the U need to be as rigid as possible, as the legs hold the wire under tension. Nickel chromium (nichrome) wire, .032 inches thick, works well as a hot wire. Nichrome is the wire used in most hair drier and toasters and is a good choice for the hot wire cutter because it heats quickly, cools almost instantly and withstands repeated heating/cooling cycles. You can find nichrome wire in craft stores. Guitar string wire is an alternative, but it has different heating/cooling properties and does not last as long.
A battery charger provides the current to heat the wire. The charger needs to provide both six and 12 volts and have a two-amp and a 10-amp setting. Incorrect voltage or amperage will cause the wire to overheat and break. In order to attach the positive and negative battery charger wires to the hot wire cutter, remove the positive and negative clamps and replace them with smaller alligator clamps. - Form the PVC into a U shape using elbow fittings. If using wood, use bolts to attach the pieces, making the finished piece as rigid as possible. Stretch the nichrome wire across the ends of the legs. Fasten the nichrome wire securely on one side of the cutter, and attach the wire on the opposite side in a way that allows you to tighten it as needed. Attaching the wire to an eyebolt allows for quick tensioning by simply turning the eyebolt.
- Cutting polystyrene foam with a hot wire cutter will produce fumes. Before you begin cutting, open a window or door to provide ventilation. It can help to have a small fan located nearby to blow the fumes away from you. Clip the positive and negative wires of the battery charger to the nichrome wire. The nichrome wire will get hot between the clips. Practice on scrap pieces of foam to determine the correct settings for the battery charger. The shorter the nichrome wire, the lower your battery charger settings will be. Allow the hot wire to do the work, and do not use pressure to force the wire through the polystyrene foam. Putting pressure on the nichrome wire will cause it to break. Check the tension of the nichrome wire periodically and tighten it as needed.
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