What kind of foam cuts well on a router-based CNC machine?
September 13, 2013 8:12 PM   Subscribe

I have a CNC machine and I usually use it to cut plastic, wood, metal, etc. But recently I've been doing a lot of my own g-code programming and I'd like to do some testing with foam materials.

Simulators and backtracers can get you so far, but at some point you have to try it out in a machine and a mistake can break a bit or worse.

I figure using foam will lower my risk, still give me something that I can hold, measure, try to use in place, etc.

Not sure what kind of foam to use, though, or where to get it? I want something reasonably rigid, i.e. not like memory foam or something, that won't get too melty when cut with a router, and that will hold some detail.

Any ideas?
posted by RustyBrooks to Technology (16 answers total)
They cut surfboard blanks made from EPS foam on CNC machines as industry standard practice.
posted by tylerkaraszewski at 8:35 PM on September 13, 2013

Best answer: Floral foam is cheap and cuts easily, but make a mess. Butterboard is made for this, but expensive.
posted by 445supermag at 8:42 PM on September 13, 2013

Best answer: Just a guess, but that stiff insulating construction foam seems like it would work pretty well.
posted by Good Brain at 8:45 PM on September 13, 2013

Response by poster: A mess is OK, my machine is contained in an enclosed cabinet with a vacuum attachment. I think I've seen floral foam cut before, maybe in that youtube video of the lego mindstorms CNC machine?

By construction foam do you mean like the pink stuff at home depot that comes in 4'x8' sheets?
posted by RustyBrooks at 8:59 PM on September 13, 2013

Best answer: Machinable Wax as per Guerrilla guide to CNC machining, mold making, and resin casting - "It is a hard, rigid, wax-like substance, technically a blend of low-density polyethylene (LDPE) and paraffin. It is not the cheapest or most durable stock, but has two important properties: it machines quickly to a very good finish with excellent dimensional accuracy; and more importantly, because it's much softer and more fragile than common plastics, even fairly major mistakes won't immediately result in a broken tool."
posted by Sophont at 9:07 PM on September 13, 2013

Best answer: I think you might be looking for the kind of urethane foam board sometimes sold under the name NC Proofboard.
posted by paulsc at 9:57 PM on September 13, 2013 [1 favorite]

Yes, I mean the pink sheets (I think I've seen other colors, like green too). The stuff I'm thinking of has a fine cell structure and is, I think, polyurethane. If you need it thicker, you could cut chunks and glue them up.

Speaking of machinable wax, I remember coming across this a while back.
posted by Good Brain at 10:39 PM on September 13, 2013

Best answer: EPS insulation board is the Home Depot stuff, pink or otherwise. It cuts well, but it can melt and the fumes are really bad for you. If you can play with rpm and feed rate you could probably get it to work.

This blue EPS foam seems less prone to melt than insulation board--maybe because it's less dense. A bit crumbly but it works well on a CNC as long as you're not looking for good detail.

Renshape polyurethane foam board is fantastic, but expensive. You can go cheaper with the low-density stuff, but I haven't tried it. We use the 15-lb density.

An electric knife does a great job of cutting through EPS, by the way.
posted by hydrophonic at 10:49 PM on September 13, 2013

Best answer: The rigid urethane foams mentioned by paulsc and hydrophonic are actually meant for this sort of machining and will cut really nicely and hold that detail even with light handling; they're the clear winners if you don't mind the cost. Floral foam, I think, would cut pretty well but also crumble and lose the detail very easily. The pink and blue insulation foams from HD will be cheap and cut reasonably well, though the surface will end up a little fuzzy and you may have to keep the RPMs down to avoid melting the stuff.
posted by jon1270 at 1:37 AM on September 14, 2013

Best answer: Everyone I have seen, in videos and in person, has used a chunk of pink or blue foam insulation panels that you can get from you local big box store.
posted by Kid Charlemagne at 5:06 AM on September 14, 2013

Response by poster: Awesome, exactly the kind of responses I was hoping for.

That instructable about machinable wax looks awesome but I will probably skip it for now. I *am* cheap but not quite that cheap. Machinable wax itself might be a good choice

I'm probably going to go with home depot construction foam though - of the above it's the most accessible, probably the cheapest and if it's likely to work OK seems like a good place to start.

More people interested in CNC here than I would have thought. If anyone's interested I've made a working CNC simulator (it works but I wouldn't call it perfect). It has saved me a TON of time, finding mistakes in my g-code. I've been thinking of making a web page for it and putting it on projects or something.
posted by RustyBrooks at 6:41 AM on September 14, 2013 [1 favorite]

Yup, blue expanded polystyrene. The urethane foam is awesome but more expensive.

If I recall, it's best routed with an endmill that had a downcut spiral so the bit isn't constantly flaking up chunks on the surface. This will give you a smoother, cleaner cut. Also, if you're doing surfaces, a ball end mill especially works like butter on the foam.

I'd love to see your G-code simulator!
posted by suedehead at 7:34 AM on September 14, 2013

Another point for the rigid blue insulation stuff. It's what pretty much anything sculpted is made out of on a theater set.
posted by cmoj at 8:05 AM on September 14, 2013

RustyBrooks, your G-code simulator sounds awesome! Please post it to Projects!
posted by Quietgal at 10:04 AM on September 14, 2013

Response by poster: OK, I will try to get something together. Until last week you literally had to recompile it if you wanted to use a different g-code file or change the dimensions of your blanks. I do have some test videos on youtube

The main thing I need to fix now to make it usable for other people is that the memory allocation is really just awful for lots of kind of complex reasons, which limits the resolution you can simulate at.
posted by RustyBrooks at 10:09 AM on September 14, 2013 [1 favorite]

I have personally machined the pink "Foamular" XPS by Owens Corning on a CNC machine using a standard V bit and it worked just fine. No melting as the bit wasn't working hard enough to heat up that much.
posted by davey_darling at 8:57 PM on September 14, 2013

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