View Full Version : foam master for mold

03-28-2008, 01:25 PM
I am in the process of building a 3 axis cnc router.
I also have 3d Studio max version 6
and was thinking about getting Cut 3D and make models.

I would like to use the 2" thick blue or pink foam to route out the model parts.
My question is can I use the Foam master to make the silicon mold
I would be using the Smooth-on brands of rtv mold rubber.

Will the rubber melt the foam?
What do you do to prepare the foam for the rubber?

Or would it be better to make a plaster block and route the design in that
and use that to pour the rubber on to.


High Seas
03-30-2008, 01:39 AM
The Smooth-On folks outta be a lot of help for this type of project. They have a great deal on trial packages - but you're limited to one purchase : (

One problem I found with silicon molds - was the number of repeat uses. It tends to loose its life and tear if not too careful. If your models could be cast in a harder mold - like fiberglass you'd get more castings. Something you'd have berre knowledge of.

For that application , you can use acrylic house paint, or plastic tape, or other specifically designed media to keep the resins from eating the foam. Some of these could also be used as a sanding/finishing filler on the silicone molds.

Best of luck, and
:cheers: Jim

03-30-2008, 10:29 PM
as a master if you don't care about surface detail. It's always going to show that porous texture. I much prefer using machinable wax, though. It is very smooth, cuts easily, doesn't make that nasty dust which clings to everything, and if you don't need your master any more, you can melt it down and make something else with the wax.

But no, silicone rubber won't melt the foam (fiberglass resin will, though.) A plaster model would look better than a foam one. There's a special plaster called Rayite that's more machinable than regular Plaster of Paris, although that can work. Dish soap makes a pretty good release for silicone rubber, but test the specific combination of materials first before committing to something important.

Andrew Werby