So, I’ve got a costume project in the wings that requires me cutting templates out of a sheet of foamex - I’m using A3-size pieces, 5mm thick. I despise cutting foamex by hand, since I’m unable to be as accurate as I’d like, so I’d love to be able to use the CNC machine to get it perfect/be a bit more fancy than I’m able to myself. Just two issues there. Number 1, I don’t know if that’s something we allow on the big CNC (and the small CNC is too small), and number 2, I’m not actually inducted on either of them, so I can’t do this myself.
Would some kind soul consider helping me out here?
I’m interested, and inducted on the big CNC, but still very new to it. Not sure if any bits would be suitable and how you hold down the piece without a vacuum table. A good double sided tape might be the best way, perhaps with masking tape if foamex tears too easily. I’m also interested in carving in polystyrene/ insulation foam too.
What exactly do you want to do? Have you got a file with the design? How many pieces, what size? Why CNC rather than cutting on laser? If ok to use in the laser, that would seem a much better option.
Any spinning tool would destroy the foamex in my opinion, what you need is a rotary cutter attachment which will be useful for textile too.
We were thinking of it since a while but haven’t done it yet.
To address that last point - going to be working on getting a file with the design, wanted to look at feasibility and options first because if I have to do it by hand that’ll drastically change the design! Unfortunately, as far as I’m aware FoamEx isn’t suitable for laser cutting because it’s PVC-based, which is a no-no for lasers apparently!
A sharp single flute acrylic blade seems to be ok with FoamEx IF it is held down properly. See discussion here: https://uksignboards.com/forums-2/discussion/advice-for-cutting-foamex-with-cnc/. Cutting into sacrificial board was also recommended. Would need to find right speeds and feeds - as always! I do like the idea of making a super sharp blade attachment, but that’s probably going to take longer to get than a suitable bit.
@Theranis, you may have to chew up a few test pieces to get it right. Holding it down firmly will be key, whatever blade or bit you use. It’s jerry building a vacuum table or using double sided tape, or perhaps using a kind of jig - a board with cutouts and tabs that could be pressed down onto the foamex that is a little wider than the cutting bit. If the pieces you are cutting are simple curves, then you could also use the CNC to make a cutting guide or jig to cut by hand.
I was looking at some industrial version - basic drag knife only needs 3 axis, so that’s ok.
Making one seems doable, and be very nice to have. But it always comes back to needing a vacuum table or other way of holding down. What to do about that?
We don’t need a 4th axis for the drag knive as it only cuts 2d profiles and we don’t need vacuum table for foamex as it can be hold down via clamps.
The vacuum table is a requirement for fabric or thin paper
A random thought came to mind…. For holding down foamex, cardboard etc., what about using snake weights - long thin tubes made of fabric filled with lead shot, glass beads, coarse sand or something similar (a bit like a sandbag, only long and thin, and can be adjusted and shaped around curves). These are used in conservation work for holding down paper, parchment, fabrics etc. as well as with rare books as book weights. They also wouldn’t be hard to make. They’d have to be carefully positioned to not be in the toolpath, but close enough to weigh down the work area. Snakes may be a bit scary though, but less so with a drag knife than with an 18,000 rpm bit on the spindle.
I understand @Federico spoke with Roman about making a drag knife. I’ve sent him some images of an STL I found of a drag knife to give him a better idea of what is wanted.
