a word about NiCr hotwire length for foamcutters

nicrFor Foamcube we use NiCr type hotwires. NiCr stands for Nickel Chromium.

The NiCr wires are strong, can handle high temperatures and do not expand too much when heated. They are also available in very small diameters so the kerf of our foam cuts can be nice and tight.

Since most Foamcube wires are either a maximum of 50 cm. or 100 cm. we use the same wire for both and simply vary the voltage running through the wires. Ideally we want a temperature range of about 220 – 300 Celcius, which can easily be achieved by using either 12 volts or 24 volts.

The wire we use has a resistance of 22 Ohms per meter and has a diameter of only 0.254 mm. It’s right in the sweet spot.

When we apply 12 Volts DC to a 50 cm. long wire, it’s temperature hovers around 250 Celcius. It draws approx 1.1 Amps from your power supply.

When we apply 24 Volts DC to a 100 cm. long wire, it’s temperature hovers around 250 Celcius. It draws approx 1.1 Amps from your power supply.

So by doubling the input voltage you can make the hotwire twice as long keeping the same temperature range. This also implies that by controlling the input voltage you can control the temperature of the hot wire.

When you build your own foam cutter it is recommended to keep your wire length at maximum 40 cm. (12 volts), 90 cm. (24 volts) 190 cm. (48 volts) etc. Power supplies in increments of 12 volts are easy to find and are a lot cheaper than having to acquire say a supply of 28 volts. By keeping the wire length a little shorter you will have a wider temperature range to cut denser type foams using off-the shelf power supplies like ATX supplies from an old computer, LED power supplies from China, or even your typical plug-in-the-wall power supply that delivers more than 1200 milli-amps.

We carry spools of Ni-Cr wire in our online store for your convenience. If you source your wire locally make sure it consists of Nickel and Chromium  (no iron, aluminium and other traces) and has a resistance of 22 Ohms/meter at room temp.

cnc hotwire foam cutting tips

In order to get the most out of your foam cutting projects we have collected some tips and experiences straight out of the lab :

  • hotwire thickness : thicker wires can carry more current and can get hotter thus travel faster , but with more heat and speed comes more inaccuracy. Keep your wires thin and speeds low for more accurate models.
  • speeds : Denser foams need more heat or lower speeds. Thicker blocks also need a speed adjustment.
  • complex models : To create complex shapes it may be neccesary to rotate your foam blocks in incremental degrees (usually 45 or 90 degrees). Keep your blocks aligned securely and perpendicular to the hotwire for best results.
  • dirt : To cut costs many people use old insulation blocks. No problem, just be careful with any dirt on the blocks that may accumulate on your hotwire. Dirt will instantly bake on and ruin a perfect cut.
  • When you have a choice, always start cutting at the top and work your way down to the bottom of the piece.