Hi

I have small homemade CNC machine and I want to try machine it.
So this is my plan: mill foam, coat with epoxy, use 2-3 polyester primer coats, sand and polish. After that semi permanent release and tooling gelcoat and so on.

Choose XPS or EPS, what is more milling friendly, more rigid?
Can I use polyester primer over epoxy? I have read that polyester don't stick very well to epoxy?