Coog - I'd be interested in the answer to your question about milling the E/G.
While I have no doubts about my spin casting method, retaining the resin in the mold, and the mold on the bench, I am worried about retaining the relative positions of channel formers. Being able to clean up the section after casting would be a useful insurance.
My gut feeling re milling it is that whatever cutter material you choose to cope with the aggregate particle - steel, carbide or diamond - it will become gummed up by the resin, even with an appropriate coolant flooding it.
I'd be glad to be shown to be wrong.
John
It's like doing jigsaw puzzles in the dark.
Enjoy today's problems, for tomorrow's may be worse.