How to make a hot wire cutter

Updated April 17, 2017

Make a hot wire cutter for carving styrofoam like a professional and save yourself from dealing with the mess that comes from trying to saw through styrofoam blocks. Make it for very little money and start yourself on a hobby that is very addicting. This hot wire cutter makes large sculptures, movie sets, and moulds for plaster or even concrete.

Cut a paint stirrer with a notch one inch from each end on one edge. Drill a 1/4-inch hole two-thirds of the way up the paint stirrer. Repeat the process with another paint stirrer, using the first one as a guide. Get one more paint stirrer and cut it in half with the saw.

Drill 1/4-inch holes at either end of a third paint stirrer, one inch from the end. Sand and then paint all of the paint stirrers the desired colour on one side. Allow the paint to dry completely and then flip them over to paint the other side. Again, allow to dry completely before handling.

Bolt the third stirrer (with the holes on either side) to the other two stirrers with 1/4-inch bolts in the holes and nuts applied to the other side. This should form an "H" shape with the two short ends of the sticks from the sides of the H on the same side of the crossbar.

Tie a shoelace into a loop around the notches on the two short ends that is tight enough to hold the sticks so that the short ends can't flare outwards past 90 degrees. At the other end of the same paint stirrers, take the magnet wire and twist it around one end at the notch. Twist the other end around the vacant notch on the other paint stirrer so that the string is fairly tight.

Stick the half paint stick into the middle of the shoelace loop and twist it. Do not twist it so tight that the wire breaks. Twist it enough to take the slack out so that the wire is straight. Tighten the bolts. Slide the end of the stick toward the middle paint stick of the H so that the H holds it in place and keeps it from unwinding.

Solder the 9-volt battery connector to the speaker wire and cover the exposed connection with electrical tape. Put the batteries into the battery holder and solder it in series with the other battery holder and then solder one of the speaker wires to a terminal. Solder the switch onto the other battery lead and then to the other speaker wire. At the free ends of the speaker wires, solder on the two alligator clips. Wrap the wires with the alligator clips around the frame of the hot wire cutter so that they do not get in your way and make sure that you clip the alligator clips onto the thin magnet wire. Make sure that the cutter is not getting hot by testing it on a piece of styrofoam.

Use a pair of zip ties to hold the battery packs to each other. Cover all of the exposed electrical connections with duct tape except the two alligator clips and the magnet wire.


The first time that you use this device, the resistance in the thin wire causes it to heat up and burn off the coating on the magnet wire. If the device does not get the wire hot enough to melt the type of material you are working with, try using a 9-volt battery. Larger batteries will have different voltages and a longer charge release time, which means that the batteries generally last longer (assuming that they are a similar type of battery as the smaller ones).


Only use this device in a well-ventilated area. Flip the switch to the off position when not in use. Treat the hot wire cutter like it is "on" as long as the batteries are plugged in or it remains hot. Make sure that the wire cutter is completely cool when you put it away. The safest way to know the temperature of the blade is to use an infrared thermometer. Never store this device plugged into the battery or turned on. Do not touch any of the hot parts or melted styrofoam (since it also gets hot and melts). Do get this device wet.

Things You'll Need

  • Four paint stirrer sticks
  • Saw
  • Sandpaper
  • Heat-resistant enamel paint (used to touch up paint on stoves)
  • Drill with 1/4-inch bit
  • 2 1/4-inch bolts and nuts
  • Shoelace
  • 16-gauge magnet wire
  • Speaker wire
  • Two alligator clips
  • Speaker wire
  • 2 4-AA battery holders
  • 8 AA batteries
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