Foam Cutter Moves Like A Hot Knife Through Butter

Make enough attempts to cut foam using whatever you’ve got — utility knife, hacksaw, serrated plastic knife — and you’ll wish hard for something that cuts cleaner, faster, and better. While there are all sorts of ways to build a hot wire foam cutter, this design from [jasonwinfieldnz] is both interesting and imitable.

If you don’t already know it, nichrome wire is nifty stuff that’s readily available in thrift store hair dryers and toasters. It stretches as it heats up, and shrinks as it cools back down.

The interesting part of this build is that instead of using a spring to keep tension on the nichrome wire, [jasonwinfieldnz] designed and 3D-printed a bow out of PLA that does the job elegantly. While [jason] was initially concerned that the bow might possibly melt, he found in practice that although the bow does get warm to the touch, it’s nowhere near hot enough to even warp.

One nice touch is the simple fence that rides along two slots and secures with wingnuts. We also like that [jason] made this foam cutter largely from scrap material, and rather than buy a spool of nichrome, he opted for a skinny heating element and pillaging the wire.

If you’re a nichrome noob, know that it doesn’t take much juice to do the job. Even though a computer power supply is what [jason] had lying around, it’s complete overkill, so you would definitely want to limit the current. Check out the build video after the break.

Still not portable enough for you? All you really need is a 18650, some nichrome, and a few bits and bobs to hold it all together.

13 thoughts on “Foam Cutter Moves Like A Hot Knife Through Butter

  1. I almost never need perfectly straight cuts on foam. I do large cuts with an electric carving knife and details with a butter knife that I’ve heated with a blowtorch.

    1. And apparently it’s still around, albeit, from different companies. Generally in the $30-$40 range based on a quick Google search. My mother used to have a Styrofoam cutter that looked something like a coping saw.

  2. I tried to build this, but I already got stuck @00:02.
    I’ve been trying to push two pieces of wood though each other but I can not get it to work, even with help.

    1. Wire EDM.
      Not titanium, not melting, but still. Also not just aluminum, fully hardened steel. Has drawbacks. Cracks love to start on EDMed surfaces.

      Recent home built Lathe with wire edm cutter hackaday article.
      Much better than twine wrapped tire table article.

      I still think someone should program an EDM to play chemical brothers. Even if they have to put a pizo speaker across the power supply caps.

  3. I think the main advantage of cutting foam, especially polystyrene, with a hot wire cutter, is that there’s a lot less mess. Cut polystyrene blocks with a knife and you get little beads everywhere, even with a fast saw, you get plastic dust that clings to everything due to static electricity building up, but with a hot wire cutter, you get a clean edge and the only mess is due to the bits you cut off.
    What’s also nice to do is bend a profile into the heating element and cut repeatable contoured surfaces, great for things like model aircraft wings.

    1. Model airplane wings are typically cut the other way. With a long tensioned wire and wooden wing sections attached to the ends of the blank.

      Much easier and allows wing taper.

    2. Back in the late 80’s early 90’s… if survived that long… I forget…. ok, anyways… I used piano/music wire purchased from the local hobby shop that was bent on the ends to wrap around maybe 1/8″-1/4″ diameter larger ~6″ lengths, notched where the wire wrapped around, that were placed at slight angles facing away from each other so could bend into a more perpendicular position on the music wire end, where maybe ~1/2-1″ protruded through to the top of the 2×2 wood handle. The top protruding ends is where I clamped my power supply and I never did… though I recall someone with theirs hung theirs from the ceiling on a rope with a long spring to have more even tension for smoother pulls when making wings or fuselage. I thought the spring seemed like a good idea since my pulls were never as smooth as I wanted them to be. Would be neat to get back into again.

  4. When i was a small kiddo (beginning of the 80’s). My father had a foam cutter that he used when he made wings for RC planes.
    The foam cutter is 1.8 meters long. Driven by a 12V car acid battery. As wire he used a normal steel wire. But he had a drive circuit made of a high power flash relay from a car 😁
    Sometimes the relay got stucked (because high amperage) and the wire got glowing red immediately 🤣
    It is still alive, living in my moms basement.

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