Milling Foam with CNC Machines

Hi there!

We recently purchased a 7-Axis Robot and are looking to create some 3D sculptures and props with our machine. Before we get started, I wanted to see if anyone had any insights or advice on materials... specifically foam.

QUESTIONS:

- In your experience, what are the best types of foam to use for milling 3D sculptures and props?
- What density of foam would you recommend for milling 3D sculptures?

Also, if you have any recommendations for the type of foam finishing / hard coat materials that we should be using after milling, I would love to hear advice on that, as well.

I would appreciate any insights or advice that you have. Thanks in advance!

CNC foam is a hugely broad term. To one person it might mean a piece of blue insulation foam from the hardware store to another person it is a highly specialized urethane material that is very expensive and used for precision pattern making for foundries and that type of thing.

Since you mentioned density, I'm hoping that you are looking for the later.

There are going to be people with more up to date information than I have, since it has been a few year since I was machining patterns. We generally used a material called RenShape or Renboard. We used a variety of densities, but I want to say we preferred about an 8 pound density. We generally used carbide endmills because the material is surprising abrasive, but we used very aggressive cutting conditions. Basically as fast as the machine would go. Your stepover will largely depend on how much hand finishing you want to do on the final product.

Be prepared for some significant mess in the form of dust and bulky chips. I generally wore a dust mask when I did pattern work, but we also worked with a lot of mdf. As far as top coat, (and revisions and fixing mistakes); we generally used a variety of Bondo like products used for automotive body work. We had a team of artists, sculptures and "hand" pattern makers that were experts at sanding and finishing patterns so I was never overly involved in that (button pusher). But they did amazing work.

6-8lb polyurethane foam works pretty well. The dust is like sand, it machines well, and you can do a lot to put a finish on it. It takes fiberglass very well, so you can cover your models with that. The foam itself can be damaged easily, so if your parts are going to be handled much you'll want to put some kind of hard outer layer on it. If you need to "sand" tool marks out of it, just grab another piece of foam and use that as a sanding block. They'll wear each other out, so your sanding blocks will need to be replaced somewhat regularly.

Hello. I have cut 10 lb foam pretty successfully. We used endmills from onsrud engaged them pretty deep and used high speed machining with rather small step over. The cut you want makes chips that look like and move like large snowflakes. There are numerous two part products that you can use to finish.

I've done several seat prototypes from this stuff that later had carbon fiber molds pulled directly from. I used the 20 lb board, its quite strong and takes details really well, even sharp corners without breakout (so long as you are careful and not aggressive near edges). easy to glue up multiple sheets with their glue and the glue machines the same as the rest.
Foam Board

The shavings are like saw dust and I just used shop vac to keep it cleaned up. Big enough dust that it didnt seem to float in the air, just fell inside the machine.
View attachment 203728

I've used a lot of closed cell urethane, like celotex. You can glue up sheets to whatever thickness you need. Works pretty good for proving out programs.

Thanks everyone for the insights and the recommendations - there's some really good info shared that I'm going to start researching.

What have you all used as a coating for these projects to help protect the foam from damage over time?

thinktankgroup said:

...What have you all used as a coating for these projects to help protect the foam from damage over time?

Click to expand...

The urethanes take epoxy or polyester resins just fine. We used to build boat stuff from it, and glass over.

The majority of the people that I have spoken to have recommended either Polyurea or Epoxy coating for our foam projects.

Does anyone have any recommendations for brands for either of these coating types? Or any recommendations for spray systems for applying them?

Thanks in advance!