Many designers, artists and hobbyists make elaborate, realistic stage props, Halloween decorations, sculpture art and other displays from foam. The foam is lightweight, paintable and easy to cut with a conventional knife; however, the easiest method of cutting it is with an electrified hot knife. A commercial hot knife foam cutter can be expensive, but you can make your own that works as well as the commercial models. The foam cutter consists of a wire that is heated with electricity mounted on a frame. The hot wire melts the foam on contact and glides through it with little resistance.
- Skill level:
Things you need
- 2 pieces of wood, 1 by 4 inches, 18 inches long
- 1 piece of wood, 1 by 4 inches, 12 inches long
- 6 nuts and bolts, 2 inches long
- Nickel-chromium resistance wire, 12 inches long
- Portable car battery charger
Shape an 18-inch piece of 1-by-4 board into a blunted arrow shape by cutting off the corners of one end at 45-degree angles. Leave about a ½ inch flat in the middle of the end between cuts. Repeat for the second board.
Position the arrow boards about 9 inches apart and parallel on a work table with the cut ends on the same side. Place a 1-by-4 board that is 12 inches long across the middle and perpendicular to the first two boards. There should be about an inch of the perpendicular board sticking out past the two arrow boards.
Drill a pilot hole in the centre of the intersection of each arrow board and the perpendicular board. Push a bolt through each hole from the bottom up and screw a nut onto each bolt. This will form an H shape.
Drill a pilot hole ½ inch from the flat edge of each arrow. Push a bolt up through each hole from the bottom and screw a nut loosely onto each one. Leave a little space between the nut and bolt.
Twist the end of a 12-inch nickel-chromium resistance wire around one of the bolts between the nut and board. Stretch the wire to the other bolt and twist the other end around the other bolt between the nut and wire. Make sure the wire is taut and tighten the nuts to hold the wire in place. Do not leave any extra wire sticking out from the bolts.
Unplug a portable car battery charger. Clamp one clip of the charger to one of the bolts on one side of the nickel-chromium resistance wire. Clamp the other clip to the bolt at the other side of the wire.
Plug in the charger and turn it to the 6 volt, 10 amp setting. Do not touch the wire and keep the wire from touching anything else. The wire will become very hot. When it is hot, you can pick up the foam cutter by its wooden frame and cut foam with the wire section.
Tips and warnings
- You can purchase nickel-chromium resistance wire from hobby stores.
- You can build many variations of this foam cutter to achieve many different cuts such as moulding edges and carving letters.
- Exercise extreme caution when handling the foam cutter. Do not touch the wire when it is hot and do not let it touch anything except foam you want to cut.
- Some foam may give off toxic fumes when it is cut. Use the foam cutter in a well ventilated area.
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