4 Axis CNC Foam Cutter Sports A Unistrut Frame

CNC Foam Cutters are capable of cutting out some pretty cool shapes that would otherwise be extremely difficult to do. They do this by pulling a heated metal wire though a block of foam. Electrical current passing through the wire heats it up causing the foam to melt away, there is no dust and no mess to clean up. [batchelc] decided to make his own large-scale CNC Foam Cutter and took a lot of photos along the way.

Since machine is 4 axis, meaning both sides can move forward/back and up/down independently of each other, tapered shapes are possible. One example where this would be helpful is cutting wings that are swept or have different profiles at each end.

DIY foam cutter made from Uni-Strut.

The main frame of the machine is made from Unistrut and measures a whopping 60 by 60 inches. Subtract the size of the mechanical components and the cutting area ends up being 48 by 42 and 22 inches high. The foam sits on an MDF bed, gravity is the only method of holding the foam down during cutting. The wire doesn’t actually touch the foam so there is no force applied to cause it to move. The hot wire moves slowly and melts the foam just a few thousands of an inch in front of the wire resulting in no contact between the two.

Both axes on each side are driven by 1/2-10″ lead screws supported by bearing blocks on both sides. The longitudinal axes smoothly traverse the length of the machine by means of skate bearings that ride on the Unistrut channel itself. The vertical axes have a plastic bushing that slides along a round shaft.

The control portion of the machine is a HobbyCC FoamPro kit that came with the 4 axis stepper motor control board and 4 NEMA 23 stepper motors. GMFC software is used to both generate the g-code and send the commands to the stepper motor control board.

29 thoughts on “4 Axis CNC Foam Cutter Sports A Unistrut Frame

  1. That’s pretty neat. Unistrut is fairly rigid over the distances we are talking about and with the tolerances a machine like this can operate under. Are there any provisions for fume exhaust? Why MDF for the base? It warps, it offgasses formaldehyde, it supports mold growth when wet and it burns. On the other hand, it’s cheap and quick to cut.

    1. Two or more coats of polyurethane varnish would solve most of the issues with the MDF. MDF warps due to uneven moisture absorption. Seal the surfaces and it can not offgass. Mold will not grow on the polyurethane. It will still burn, but would be hard to ignite. The best attributes of MDF is its rigidity and flatness…great for CNC machinej base applications.

  2. i did see a slight issue – the piece looked like it shifted a bit when falling to fill the melt-gap a few times (at the right end of the cut from the camera’s POV) the small wedge underneath fell away, for example. this might be alleviated by cutting pieces from the top of the starting block of foam rather than the bottom…

    1. The only solution that I can think of would be to use gravity to your advantage. Support the block from the top, cut the wing bottom surface first leaving the last bit of trailing edge. This leaves the foam hanging, then cut the top surface and then the last bit of trailing edge free since its accuracy (covered by flaps/ailerons) is least important.

    2. I see that kind of shifting shown in the video a lot when cutting foam. I’m not sure why it occurs (I heard it explained as “internal stressors changing” – sounds interesting but I don’t really know what is really happening). As you cut the upper arc of airfoil it tends to pull up at the leading and trailing edge. I’ve noticed it also tends to balance out when you make the lower arc of the airfoil, leaving you with an airfoil that’s very close, if not identical, to the airfoil intended.

      My solution to the problem of shifting and movement in general is to lay a sheet of scrap counter-top granite on the foam being cut. It weighs nearly 20lbs, which is fine for the foam, and leaves no chance of movement. The moment the wire cuts through, the gap pressed closed by the weight. There are rare times when the core and the shell will bond, but never so much that they can’t simply be pulled apart.

  3. “… pretty cool shapes that would otherwise be extremely difficult to do. …” You can say that again. I tried stuff with a coping saw and all I ended up with using a lot of smoothing of edges and finally throwing the stuff away. Still I wouldn’t be able to afford one for the occasional work I do, sigh ;-)

  4. It’s not true that the wire never touches the foam. The foam will fall as pieces are detached and so it will end up falling into the wire.

    now, gravity may be enough to hold the block of foam in place for normal use, but that’s not the same as saying that the wire exerts no force on the foam.

        1. how would that be any more exact? a tightly stretched wire is VERY straight (although if they are moving the two sides independently, how do they account for the different distances?)

          Lasers would not be more accurate than a properly tensioned wire, and would have the same problem with material falling as you cut away it’s support

  5. Submitted this link a few days ago for the _other_ CNC foam cutter– on a roll lately with foam cutting, huh? Here is a link to an instructables that builds something very similar. This one does not have a frame– you attach each end to a desk or other work surface. It should give you very similar functionality with independent control of both ends of the wire.
    http://www.instructables.com/id/Make-a-CNC-Hot-Wire-Foam-Cutter-from-parts-availab/

  6. The linked article is 5 years old. It would have been nice to see some follow up info in the post here. For example, are the electronics and software still relevant? (or even available?) Is the device still in use or has the creator moved on to something else?

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