New Mythbusters CNC'd mold?

[AndyJ]

In the new Simpsons episode of Mythbusters they create a two-part mold of Homer's head on a CNC mill out of urethane foam. I was wondering if anyone had any experience with this technique, specifically after the mold is finished it appears to be hardened with some sort of bondo or resin, and I'd love to know that materials and techniques to doing that.

There are lots of guys here with CNC routers that I bet would love to know how to make great molds with their machines!

 

[Moviefreak]

Maybe someone could PM you with an accurate description on how to do this... asavage

 

[8 perf]

Haven't seen the episode, but its likely "Styroplast" or something very similar. Its used a lot in the themed entertainment industry to harden foam based sculptures.

 

[AndyJ]

I just looked up Styroplast, and it does indeed look like that could be it, perhaps sprayed on. Here are some photos of the raw foam and finished mold, which are suspiciously a similar color, though in the episode there is a very audible "thunk" sound when they handle it. They also brush on latex as a skin when they cast the piece.

 

[NormanF]

It's an 8-piece mold. I assumed they used RenShape or a similar material to machine the mold from and you might not need to do anything to treat that before you cast in it (at least for a one time cast) but I do not know since I don't want to spend that kind of money to find out.

 

[AndyJ]

Welllllll, you can see in the photos I posted above its clearly rigid foam. However, that doesn't mean that was the final material.

 

[cray]

+1 Renshape or similar. It comes in many different densities, the higher end of the scale can take really fine detail and is strong enough to be used for vacuum forming without being crushed. No need for it to be coated with anything. It's closer to timber or MDF rather than light weight blocks of insulation foam and the like.

Bit of info here: http://lcamtuf.coredump.cx/gcnc/ch4/

 

[AndyJ]

I found Smooth-On's Epsilon foam coating and contacted them about it. They said coating urethane foam with it, it should be an excellent mold for silicone or flexible two-part foam with the right release. Planning on doing some tests soon!

 

[nicom1234]

Id have to agree with that it is 'RenFoam'. When Ive used it in the UK, we called it 'chemical wood'. Its a great material for machining and is almost like a very dense, incredibly fine grained wood.