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! :)

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.

Comments

[mperry07]

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.

[nitroeh]

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.

[swskamp]

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]

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?

[AndrewHazelden]

The temperature of the hot wire affects if you get a clean cut or a furry coating that has to be sanded off.

[indianmike]

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.

[anwrks]

This sounds perfect! Could you tell me how you connected the wire to the jumpstart?

[colinmcc]

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.

[crjeea]

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

[heathbar64]

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.

[samchamb]

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 .

[tricky68]

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

[samchamb]

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 .

[samchamb]

I can confirm that a hf (smps) lighting psu works well .

[jake14]

i'm no genius but what about rewinding the secondary winding on a microwave transformer to 12 or 24 volts using either a 10 or 12 gauge wire. it isn't the voltage that matters but how many amps can be produced. A microwave transformer will easily put out 6 amps if not 10. i will let you know as soon as i get a chance to try it.

[llulu2]

i have a question. i bought a transformer two thin yellow wires and the other side has black, red and yellow thick wires. how will i know if it's DC or AC . Or rather which wire will i use for connecting the plug in's and to the hot wire? :x need help. :D

[Nawaz]

A transformer is an AC-AC converter. Meaning that you input an AC and will get an AC output but of a different amplitude.A transformer can work both ways. In your case, I would say that you want to step-down your mains to a lower value(example 240V to 12V). In this case, your input will be the two thin yellow wires and the output will be the 3 wires on the other side.

Since there are 3 output wires. It's will be something like 12-0-12. Meaning that if you use any of the left or right wire with the middle wire, you'll get 12V output, but if you use the two outermost wire only(without the middle wire), you'll get 24V.

A bit confusing, but i hope it helped :)

[rmndela]

HI,

Forgot to post my email address.
[e-mail].

[rmndela]

Hi,

I have just finished assembling and testing a Hot wire foam cutter.
Works perfectly in cutting large junk styro foam materials into thick slabs or thin slices or into any form.

The power supply is quite sturdy at 6 amperes and has fully-controllable current output to vary the heat of the nichrome wire.

Most of the parts were just salvaged from junk electronics products and few parts were bought from an electronics store. The circuit is easy to assemble for those who could follow instructions.

Please email me if you need further clarifications.

Rod

[mikesnyd]

OH ya. and the secondary leads off the transformer are two greens and a green with a yellow line. The two greens are my source of the 24V 2A. and i think the grn/ylw is ground but i am unsure. The schematic it came with didnt even tell me.

[johnny3h]

I have been "fiddling" with electricity for about 55+ years and I THINK that third wire on the output side of the transformer is what is called a CENTER TAP.

A Center Tap is a wire that is connected to the transformer winding RIGHT AT the middle. As other commenters have mentioned, when that wire is used in conjunction with one of the other [end of the winding] wires you get PRECISELY ONE HALF [1/2] the voltage, AND if it is wire "like a ground" on two seperate circuits each connected to ONE of the winding "end" wires you get TWO seperate circuits of one half the specficied voltage each.

If you just use the two end wires then you get the full rated voltage.

Again, I'm an electrical/electronics novice, but this is the way it was explained to me. Hope this helps for novices to understand "Center Tapped" transformers.

By the way, transformers can be ordered with several taps [on both the secondary (output) and primary (input) windings to obtain many combinations of voltages and current outputs].

[dazedonblu]

This is great I've now built an industrial quality one for a friend that owns a gun shop and he is now making custom fit gun cases out of those cheap 20.00 cases by upping the charge for the "custom fit",weapon case. Its kind of a rip off for him to do it but some people are too lazy and have too much money and would rather just have it all done for them. But these are the plans I used and it cost me ZERO dollars to build it because I used all scraps and things I had around my house these plans(http://www.ar15.com/forums/topic.htm...=292695&page=1)
.The only problem I've had is figuring out just the right wire. I used an old #1 e guitar string. But if anyone has any suggestions let me know. I would love to turn this into an automated CNC type system but it's in the drawing phase, and any input will be greatly appreciated. All I have is a regular PC an a free CAD software. Well thank you all and I hope these help(This is not design and I take no credit for it.)

[Wyoming]

For anyone looking for nichrome wire: I picked up a small "personal" type electric heater from Goodwill. The kind to look for has the coiled elements. They look like long springs. I imagine that hand-held hair (blow) driers would be a good source, also. Curling irons, maybe, although I have yet to tear into one to find out... Once you get the element free from whatever ceramic affair it is wrapped around, unwind the spring between your thumb and index finger until you get the rough length of heater wire you need. This will get out most of the kinks. Thread the wire through a small hole in a scrap piece of wood (like lacing a shoe). Pull the wire back a forth several times, let the friction warm it a bit, and it will straighten out nicely. I got over 20 feet of wire from the first element. There is a second in the heater just like the first. Hope this helps those who have no easy source for resistance wire.

[formman]

I make floralforms for florist. Been doing this for 21 years. I have found that a
great place to get wire is the local welding supply house. .025 or .030 high
grade stainless steel (316 or 316L) (L is for low carbon) or Inconnel wire
works great. Plus, a good power supply is a small 2 (two) amp battery charger,
or for longer wire operations a 40-200 amp will work.

[waltbosz]

I just harvested some nichrome wire from a broken toaster. I also harvested two Mickey Mouse branding iron from the same toaster. Note: do not buy appliances from The Disney Store; they will set your house on fire.

[mikesnyd]

So i made this wonderfull little contraption you have described. I have a light dimmer and a 24V 2A transformer. I initially had a #10 guitar string as my wire but i broke it and was told to use this 80lbs test fishing line(its steel). Everything was running smooth until about 5minutes of operation. i was in my third cut when my transformer started to smoke. I have not been able to get the thing working again. So do i unwrap my transformer and re wrap it or just go get another one? How may i put a safety catch in there so as to protect this from not happening again? And as for the thrid wire comming out of the secondary side of the transformer.... do i ground that wire? your diagram had this left alone. Maybe i am just lucky enough to have a crap transformer. Have a happy happy day eh. Sweet build man.

[Audiyoda]

On almost all transformers the secondary lines can be configured for full voltage or half voltage. Generally the two same colored wires are full voltage (in your case, 24V 2A - green and green), combining two different colored lines will result in half the voltage (in your case, 12V 2A - green and yellow). You will always have that third line 'free' in a single pole application like this. I always tape it off so as to no cause a short.

*A Transformer doesn't require a ground - your work should still be grounded, but not the transformer.

[bricabracwizard]

Great hot wire! Thanks for giving me the idea of using templates for a better finish, I've always done freehand with not such a good result.

[Evilthingamabober]

Umm, I have a nibbler from Futurama, will that do?

[giventake65]

what is the use of a nibbler in this project?

[msmith9899]

Hey flywoodkb, thanks for posting this. I made a hot knife based on your design for a foam project and it worked great! I featured your instructable on my web show. If you would like to check it out, it's at http://www.tectherobot.com/shows/tecs-toolbox/foam-sculpting-hot-knife/ Thanks again

[balisticjoe]

Is this able to cut through foam-board? Not sure if it would make it through the paper like parts.

[carloriolo]

Hey Guys - I just wanted to send along a friendly link to my website http://hotwirefoamcutterinfo.com After reading this tutorial, I had ALOT of questions. After a few months of research, I made my own website just to share :) Enjoy

[LPittman]

I desperately need to source one of these transformers, but I've been everywhere in New York and can't find anything close. Can someone help me out as to where to get my hands on one?

[guru_florida]

The green wire is typically earth ground, as in attach it to your metal project box ( if used.) The purpose of this wire is if any electrons are passed through it (i.e. if there is any voltage difference between the earth and this wire), it will trip the breaker! It's a safety feature of three prong electrical systems.

There are three wires used in AC, Hot, Neutral and Earth Ground. It sounds like you are using this green wire as if its the AC neutral wire when in fact it is Earth Ground. In DC, we talk about ground being the return path to our electrical circuit, but this ground is not the same as Earth Ground. In the U.S./Canada, AC neutral wire is usually white and black is hot. See the following link for AC color codes:
http://www.allaboutcircuits.com/vol_5/chpt_2/2.html

[STBro]

 All transformers are AC in and AC out.  An autotransformer with a variable output is called a Variac or variable autotransformer.

If the device also converts AC to DC, then it includes a rectifier and can also include a transformer before rectification.  It is also called a DC power supply.  If the DC power is clean and maintains voltage or current, then it is a regulated power supply or linear regulator.

You can use either AC or DC to heat a wire.  The wire acts as a resistor.

If you use a light dimmer with a transformer, you should "derate" the transformer (by selecting the correct wire resistance) so no more than 70% of the rated power flows thru it.  Also, do not use the lowest setting on the dimmer.  It will severely reduce the life of the transformer.   A fan "dimmer" used to regulate fan speed is a different type of device and it is suitable for use with a transformer.  You still need to make sure it has enough of a power rating.

If you feel any tingling when using electrical power equipment, the rig is unsafe and should not be used until the safety problem is found and corrected.

[tb17mccoy]

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

[steve cook]

OK we just built ur home made hot wire cutter and I find for small projects it is great but the wire u used for cutting keeps breaking after short usage and should we be yousing the ground wires ? ur instructions did not say what to do with them. but I must say it is a great do it ur self project it was easy to put together and ur pictures wear a really big help and ur prices for the parts wear almost on the penny and I defiantly would suggest to any one how is looking for a small project hot wire to visit ur page thanks so much

[_-MacGyver-_]

dude, go to home depot, and get some 16 gauge wire, that stuff wont ever fall apart

[charliey]

7862 Tony ---- what's this "VARIABLE Electronic Transformer"? You don't mean a Variac, not at $20 Oz, for sure.
Not sure I understand the "downlights"
Would be obliged for further info.