Picture of Hot wire foam cutter
Cheap ($30+-) and easy to build hot wire foam cutter made from commonly available parts. Cuts styrofoam for surfboards, model plane wings, sculpture, model train or tabletop wargame terrain, 3D sign letters, mold models for lost foam casting, etc.

5/17/2007, Important note! Please be sure to read the comments that other users have left below. There's a LOT of good info there. Check out the links that folks have posted and study what they've said here and you will be able to build a cutter thats suited to your budget and the materials you have access to. There are a lot of alternatives listed or linked below for the frame, the transformer, the wire, the enclosure, and the heat control. Don't underestimate the power of comments! :)
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Step 1: Parts

The parts should be pretty easy to find.

1. 12 foot, 16 guage extension cord, about $2 at Home Depot

2. 2 wooden yard sticks from the Home Depot paint department, $.97 each

3. 4 #10-24 x 1.25" machine screws with nuts, $1 at Home Depot

4. 10 #10 washers, $1 at Home Depot

5. About 12 feet of strong, low-stretch string. I used 200 lb dacron kite line.

6. A single-pole dimmer switch. About $10 at Home Depot.

7. A 25 volt, 2 amp transformer, $10.49 from Radio Shack.

8. An electric guitar string, about .10 - .16 size. I think around $1? You can get these individually at a music store or you can use either of the 2 smallest strings from a packaged set. You should keep a spare handy because they can burn out or break from too much tension.

9. A length of two conductor electrical wire with a regular plug on the end. I salvaged mine, but you could use another extention cord if you like.

10. A piece of wooden dowel or stiff plastic rod about one foot long (not shown). I used a bamboo skewer.

11. Optional: 4 regular-thickness CD cases. These are for the box that holds the transformer and dimmer switch, but you would be much better off with something like a "project box" from Radio Shack.
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tb17mccoy4 years ago
I did everything in your instructions except I made my frame out of 1/2 ' pvc but everything else I did as you instructed including the crappy plastic box. I couldn't  find a 120v 25 with only 2 amps so I used a 120 24v 40 va transformer and put a 3 amp fuse on the hot side between the dimmer switch and the transformer. I tested it in my Garage and all worked well. I cut a test piece of foam cut like butter. Thanks you saved me about $ 140.00

Actually, a 24volt 40VA is LESS than two amps. Glad it works. May I suggest you post it as an instructable?

jwhitten7 months ago
I'm surprised no one has suggested putting a small low-wattage light bulb in series with your hot-wire to act as a current-limiting device. That would sure save a lot of blown transformers and dimmers.

That IS an excellent suggestion. Also, as another commenter suggested, a fuse for safety/protection of the transformer.

colinmcc2 years ago
There are several reasons that folk may be be burning out transformers.

The resistance of the cutting wire may be so low that the transformer is trying to supply more amps than it's own wire can carry, and so, just like the cutting wire the windings in the transformer heat up/melt.

Transformers are AC devices, they like a nice rounded (sinusoidal) waveform as input. Some cheap (expensive as well as cheap ones) dimmers can output a very square waveform and effectively put pulses of DC into the transformer's coil.

Dimmers probably use a triac, which controls the conduction angle of the input sine wave. The output waveform is not sinusoidal, unless the dimmer is turned all the way up. The net effect is to produce high frequency components along with the low frequency line voltage. If the high frequency portion contributes to core heating, then this could have an effect on frying the transformer. But I think there is simply too much current. The only way to know for sure is to take some AC voltage and current measurements and find the power in and out.

Would it be possible to use the dimmer on the OUTPUT of the transformer? It's still AC, and I can't imagine that the triac, etc. would care

rblythe847 months ago
Great article! Can I use my soldering gun as the power source? I read of some people who use their soldering gun and use a dimmer to control the heat. Is this feasible?

Actually, that should work fine.

naopak_lik3 months ago

I am sure I wired all things like on diagram but it is not working at all. There was no smoke, nothing. I have voltage before transformer but nothing after. Can it be because I am using electonic transformer.

By "electronic transformer" do you mean a "wall wart" power supply or "brick" power supply? If that's the case, you cannot use the dimmer. The dimmer requires an old school, iron transformer such as what is specified

mithun14321 days ago

my hot wire cutter is not working

armorer2431 month ago
For a power supply, I just used an old ATX power supply from a dead Dell PC. Using NiChrome wire and this calculator :

I was able to get very close using the calculations alone and fine tuned it from there. I am using 10.4 inches of wire at 5vdc and it hits 620F along the length of the wire. Perfect cutting temp on everything from 1/8" sheets to 8" blocks. Consumes a touch over 2A, which is well within the 27A the PSU is rated for on the 5v rail.
rongterlee1 month ago

May be we can choose professional hot wire cutter from manufacturer .(

Rongter company concentrates on developing and
producing the various
Heat Cutter, Hot Wire Cutter, 3D Cutter
for chemical,
textile, construction material. With 10 year experience, we can supply customer
with the various good quality heat cutter to meet indoor,
outdoor and in-plant cutting needs

electric heat cutter including Hand-held tool, Bow cutting tool,
Table cutting tool, Hot wire cutting tool, 3Dcutting tool.


1.Expanded plastic: EPS,SIPs ICF,
EIFS, Sponge, Foam etc.

2.Wires cable, Rubber, PVC tube,
Nylon rope, Non-metallic belt, Aluminum foil, Metallized film, BOPP film etc.

3.Textile, Fabric, Leather, Carpet,

4.Packaging material, Thermal
insulation material, Inflating film, HDEP. Cushioning material etc.

order to expand our business line, we would like cooperate with you and supply
you hot cutter in best price and good quality.

Thanks & best regards

Robert (

Hot Sales Cutter.jpgHot sales cutting tool.jpg
degen11 month ago
I made a similar hot wire cutter, but I put mine in a Tupperware container. I also added a fuse for safety.
j_remmi9 months ago
Hey. You're not kidding about turning that dimmer slowly. I found out that if you get impatient and crank that sucker quick, you hear a "pop", then it no work no more.

I friendly reminder from one of the foolish. :D
gargamal11 months ago
what if you wanted to cut a tree stump ? I want to build one that could burn though a tree stump in a hour . I am guessing I would need a full 110 volts and 10 Ohms resistance on the nichrome wire. I don't know ifs even possible but am looking forward to trying
stowie1 year ago
here is my simple design: Was given 32 awg nichrome wire from a friend (cheap on ebay), wood (furring strip 8') fashioned into a "C" shape - I strung the wire at the end across the opening, hardware to attach the wire to the supply voltage (drilled through the wood and tightened the hardware to it), used the following power adapter from Lowes:

Which is essentially a step down transformer from 120VAC to 24VAC with a constant current output. Initially the wire secured across the opening was 2'8" long. The wire did heat up and did cut foam but at a slow rate. I realized that the wire would get hotter if i shortened the wire. The opening was shortened to just under 2' which made the wire the shorter. Now the wire heats up to a hotter temp and cuts much easier and at a faster rate. The setup should only cost between 25 to 35 bucks considering that one has the hardware (nuts, bolts, washers, and lugs) instead of having to purchase large expensive packages of hardware that is generally sold today instead of individually. Built this for a friend. He says it works great.
Aiyion1 year ago
I really like this simple cutter-tutorial. But is there a way to find a well working combination of wirelength, thickness and a not exploding transformer? ( try'n'error seems to be a little expenseive :D ) I want to build something like a cnc-foam-cutter for my 3D-Box and do not want to spent that much money on useless "pooof"s. If someone is interested in getting and sharing ideas about foam cutters he would be welcome on my Blog:
I have a pair of 120/12V 4A transformers. 4A is not enough current. Does anyone know if they can be used together to get more amps through a single wire?
If they are identical, you can parallel them to increase the current output. (hook each of the two imputs to its companion, and likewise the outputs.) If they aren't identical, I wouldn't try it.
aaastikae1 year ago
i've tried but my transformer blew up. i've founded that hot wire foam cutting technique is not safe anymore. if any one have suggestion here please feel free to comment. it will be much better if you give me the process how to hot wire not blowing anything.
In order to help fellow constructors and my friends please check this helpfull page about DIY hot wire styrofoam cutter
mperry073 years ago
I made the hot wire foam cutter, it works great, for about a minute or 2, then there is a pop and a puff of smoke from the transformer. I've blown (2) Radio Shack 25 volt, 2 amp transformers. Dimmer switch is set to 1/3 or no more that 1/2 open. Does anyone have a solution? No more transformers left at Radio Shack.
In order to help fellow constructors and my friends please check this helpfull page about hot wire styrofoam cutter
I am using the same setup and experiencing the same issue with the tramsformer burning out. Were you able to find a solution? I've blown 2 so far.

Any idea what I might be doing wrong?

Thanks in advance.
nitroeh, what type of wire and diameter are you using?
swskamp nitroeh2 years ago
Your wire may be a little too thick. I had great results with a very thin wire like a guitar string. I could cut all day. Used some .035" Mig Welder steel wire and didn't cut 5 minutes before I burnt the transformer up. I'm currently looking for a transformer with 5 amps output to be able to heat up the larger wire.
leea9 mperry073 years ago
That would be only 50 watts. 50 watts does not sound like enough this size. I am trying to make a 3 foot cutter. It takes 3-4 amps. That much would blow a 2 amp transformer.

My problem is that when I cut I have strands of plastic trailing off of the cut edge. Why do I get those?
The temperature of the hot wire affects if you get a clean cut or a furry coating that has to be sanded off.
social1 year ago
In order to help fellow constructors and my friends please check this helpfull page about hot wire styrofoam cutter
anil0071 year ago
I am using the Creative 12V AC, 2.9 Amps, is it usefull in Nicrome,guittar wire. Or i have make the circuit. What i do in my cake. if i am using small wire it melt. may the power will be reverse it may be cause failure of transformer.
lanwantek1 year ago
Did anyone use a fuse to protect the transformer?
indianmike2 years ago
I really admire this person's design,but I have a simpler way. I used stainless steel wire feed .030 welding wire and connected it directly to one of those 12 volt jumpstart battery packs I had in the garage. The cutting wire instantly turns a brilliant orange and cuts 2 inch foamboard like a red hot knife through butter. Much simpler and cheaper, and if I need to jumpstart a car I've got that capability. I've made 50 or 60 long cuts and the battery pack still shows full charge. I love simple, I adore multipurpose. Try it, you'll love it.
This sounds perfect! Could you tell me how you connected the wire to the jumpstart?
crjeea2 years ago
for smaller or lower current applications, take a length of electric fence wire and pull out one of the thin pieces of wire and use that instead, not quite as strong it you force it too much but then again most of the time you buy electric fence wire in 100-200m roles extra to that's going to give you probably about 1000m or so.
(great for polystyrene) it will run fine even on a 9V pp3 or a bike/car battery... mains adaptors often cant supply the current needed for larger ones but a car charger will do fine. (great if you are out side making adjustments on the fly or your shed doesn't have mains (or a cable that reaches) ... or you just hate people unplugging it when your half way through :D
heathbar642 years ago
A while back when I first became interested in this, I discovered somebody on e-bay was selling nichrome wire in small bits. Like a few feet for a dollar. this is perfect for somebody who just wants to try it a little. Of course since then I have salvaged a ton of it from different heating appliances.
samchamb3 years ago
Has any one tryed useing a hf lighting p.s.u with a dimmer ? I will try this and report back . the unit I have spare can suppy 9.2A @ 11.4vac and is dimmerble .
They also have thermal protection .
Can you please elaborate on what the "hf lighting psu " is I am very interested in building a cutter and any helpfully hints are much appreciated. Thanks
HI tricky
The power supply unit I have been using is basically a 12v halogen lighting transformer , these use high frequency (hf) switching to drive a high frequency transformer . they are cheap and light . I wasn't certain how much info you wanted .
I notice that some of the other posters are calling them downlighting transformers .
please read some of the other comments as there are lots .
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