DIY Foam Cutter Makes it Too Easy

Cutting foam is pretty tricky without a hot wire cutter. Don’t have one? Well, lucky for you, [Darcy Whyte] has a guide on how to make one. It takes just over an hour to build, and it costs next to nothing in supplies!

[Darcy] is using an old 9V power wart that he had lying around, but you can probably use any DC power supply. He designed the frame in SketchUp and cut it out with his CNC router, although a saw will work just as well for MDF. A piece of 40 gauge nickel chromium wire was strung taught between two 1/4-20 bolts, with one held back by a spring. The spring acts as a safeguard to prevent snapping the wire during overly aggressive cuts. This may be a simple build, but it does produce a handy tool.

[Darcy] demonstrates cutting foam with his creation in a video after the break. We think he could cut thin plastic with it as well—modify your 3D prints, anyone?—though he may need to crank up the voltage a bit.

If you’re interested in building one yourself, [Darcy] has also provided the frame templates on his site (SketchUp files).

37 thoughts on “DIY Foam Cutter Makes it Too Easy

  1. Reading this right after the crayon lathe item and … hold my beer, I’m gonna try something.

    (Well, not quite… the nichrome won’t be in until Tuesday, but I’m really glad I ordered the extra length now.)

    1. Glad you like it. I just posted better sketchup files given that people seem quite interested in the machine. If you need any help feel free to ping me!

      1. I’ll be building by hand, so I’ll probably just riff on the concept, and add a spindle for the foam along the way. I have some reasonably thick foam, and know that I can create unreasonably thick rods/columns with spray-in insulation foam, and the same order that brings the nichrome was inspired by a sale on four-packs of steppers … so there’s a spare or two around now, and thus the time may have come for either a foam-lathe or an unusually well-padded fail.

        I wonder what size I can get away with, given how crowded the shed is….

    2. Nychrome actually tends to break alot more then really thin steel wire. So there is that. If you have access to small gauge metal guitar stings they actually last longer then nychrome. however you cannot get them as hot before they fail (you don’t to get them that hot)

  2. When I made my foam cutter didn’t find in my house any suitable transformer. Either get my wire red hot (too hot to make a decent cut) or didn’t get hot enough.

    What I found to work great was to use a light dimmer and a 12 volt transformer (the ones used for halogen lamps).
    This setup gives you more power, needed in the case of thicker or longer wire, and the ability of controlling the temperature of the wire.
    The components are cheap and easy to find, the setup is simple, and you can use the great structure Darcy designed.

    Here is a blog entry of when I made my hot wire foam hand saw. Sorry it’s only in Spanish. http://comomcgyver.blogspot.com.es/2007/11/cortador-de-hilo-caliente.html

      1. that’s the way that I did it.
        made a really long throat (about 18 inches) so I can get to the middle of large pieces, and I can just slide the power connection along the top rail of the device where the bare nicrome sits, (easy variable power).

  3. Always only use power supplies that provide adequate isolation from the mains voltage of course! The small but powerful supplies that modern gadgets come with, are switching regulators, they will not always provide isolation. And if you use one of those, you might have 9V over your wire, but when you touch it you might touch a connection to your live mains wire …

    1. if by modern gadgets you mean phones, tablets, etc. there is only one reason for them not to be isolated, that is if they are broken

  4. While making mine, I found the spring was needed to put tension on the wire as it elongated while heated.

    Also, a good source of ni-crome wire is an old hair dryer. I just put a nail in the coil, while unwinding it, so that it would be straight instead of just pulling and having kinked and spiraled wire.

        1. Seems like good prices… probably fast ship too. I use ebay which is slow but I don’t mind. I have 10,000 projects going at once, I can always work on other stuff while I’m waiting. :)

  5. I had V2 of the machine in the works but given the interest shown today, I accelerated it and published it. Even easier to make. I’m cooking up some kits for some friends and I couldn’t control myself, I made a bunch of improvements. I published the sketchup file. :)

  6. FWIW, I’ve also heard of people using stainless steel wire for their cutters. They get it from either welding shops or picture hanging kits.

  7. highly recommend variable AC power supplies, allows you to adjust the voltage to match the different temperatures required to cut various foams (EPP, EPS, and Corning Owens all require very different temperatures to cut well). Also allows you to change wire length to better meet your project

    1. You’re totally right a variable power supply is way better. I’ll likely do one up with one and will add that to the post. I just happen to have a box of wall warts. :)

  8. Nichrome (nickel chromium) has a much higher resistance than steel wire. So to use steel you need a power source that delivers more current at a lower voltage and such a power source is far less common.

    Nichrome also stretches a lot when it heats and hence the need for a spring.

    Although nichrome stretches as it heats, it does maintain it’s tensile strength quite well. Steel however, looses most of it tensile strength as it get hot.

  9. Sorry for the new question, but I downloaded the templates and can’t view them. How can I view your sketch up files?

    1. You can view the sketchup files in um…. sketchup.

      Actually, I can put up some pdf files if you want. Would that help? But I’m out on the road right now so you’ll need to send me an email with a reminder so it gets into my inbox/todo list.

  10. Nice post!

    The polyurethane foam cuts very cleanly. Building the frame doesn’t seem too hard, it’s a good thing a friend has a CNC router.

  11. Did anyone ever consider measuring the resistance of 12″ or the wire they want to use? You need approx. 7 Ohms. No matter what wire u use, can be made to this ohmage. Guess how this can be done. There are numerous ways. THINK!!!!!!!!!!!!!!!! Keeps you from aging!

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