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Nichrome Wire foam cutter/heater

  1. Dec 22, 2016 #1
    I am planning to build a foam cutter by heating up a piece of nichrome wire. I found that nichrome has a relatively high resistance compared to other conductors and it is the reason why it is used as a heating element. That is what confuses me because I think it only applies for constant voltage sources, but I've seen DIYers online using a battery directly with the wire.

    If I use a constant voltage source , then P=V^2/R and the smaller the resistance the higher the output power and the wire will heat up faster. A high resistance wire like nichrome doesn't seem to be the ideal type to be used for a constant voltage supply. I've seen diy foam cutters online powered directly by 9V batteries. How does it work? If a nichrome wire works for a battery, then a lower resitance copper wire should work too, as long as it isn't lower than the battery's internal resistance.

    A constant current source is more suited for a high resistance wire, since P=I^2R.
  2. jcsd
  3. Dec 22, 2016 #2
    I've used these wire cutters a lot . Nichrome is used for a reason , just because of this high resistance , it's a good match for a 12 V source .(car battery).

    If you used copper wire the resistance is very low , so you need a 1 or 2 volt source to deliver about 4 Amps not easy to find ..., also copper is not strong when hot (or cold) it will break !!

    Don't worry about the theory too much ... first you need a power supply , Ideal is a bench , mains powered , variable supply at least 4A 12V , you can vary the output to get the right temperature.

    Tell me what you have already ...have you bought the wire? what about power? how long does the wire have to be to cut the size of foam ? what foam , expanded polystyrene ?
  4. Dec 22, 2016 #3
    Thanks for the reply. I haven't bought anything yet. I wanted to read and ask about it first.

    What if I used a 9V battery and a copper wire then use a potentiometer to regulate the current to 4A. Will the copper wire heat up? I'm asking this just to satisfy my curiosity, so let's neglect the possibility of the copper wire breaking for a wile.
  5. Dec 22, 2016 #4


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    You don't necessarily want the wire to heat up quickly. What matters is the temperature is the right temperature. Too cold and it takes a lot of force to pull the wire through the foam and you need a lot of tension to keep the wire straight. Too hot and you can easily burn grooves in the foam and the cut is wider.

    I once used a 12V battery and the speed controller from an electric model plane to control the temperature of the wire. I've also used combinations of car light bulbs as resistors to drop the voltage if necessary. Some people have used PC power supplies.

    Lots of good videos on youtube.
  6. Dec 22, 2016 #5
    very true CWatters heating up quickly is not an issue ... we 're talking 1or 2 secs , once the cutting starts the temp is constant ... It's important you tell us what you have at hand ... it could be done with iron wire ... I have some very cheap galvanised iron wire , about .. 0,5 mm from a local shop , works fine , and as Cwatters said if you don't have a variable supply you can put many things in series to reduce the current (from a car battery) ..

    Number one question how big are the cuts you want to make ... how long will the hot wire be , this will determine everything else.
  7. Dec 22, 2016 #6


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    This Staco 3PN1010 autotransformer would be your best choice for a power supply IMO. I have one of these that came from a business that did foam cutting.

  8. Mar 21, 2017 #7
    Hi, joined this community to say, "Thanks!" I have a bench power supply and have been looking the last couple of days for this answer about using it and nichrome wire to make a glass bottle cutter as seen here. It looked like what they were using, a bench power supply: http://www.esemgoldex.com/youtube/v/f34fcDiiZYw/ There are other videos of guys spinning the bottles cutting through not using cold water, but they didn't show the set ups.
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