CS: I haven't heard of this group : do you have any contact for them?
Ian : No , I've got far too many projects to go that way
though its not a bad idea in the future. There are some excellent articles on home foundary in the old ATM series of books published mid last century by Scientific American.
I'm designing polishing tooling for a 32" mirror. I will probably go the route of aluminium sheet faceplate with tack welded triangular strengthening ribs on the back.