Jah Boss - I "pinned" a few parts when working at an optical shop back in the 70's to the boss's dismay until I figured out that the down stop bolt on the overarm was unscrewing during runs from vibration and letting the quill jump the socket and come down on the parts. I put a lockwasher and nut on the down stop and stopped that. You should check your overarms and set the down stops before starting a run to make sure the quill tip only comes down low enough to engage the driver socket and not low enough to pin your parts.

If you machine your cast iron grinder to a CX radius, you should make a matching CC grinder so you can grind them together with SiC to true them to each other and get them both truly spherical and on radius. They will grind each other a lot faster than trying to true them using glass; the wear rate is something like 100X faster on glass than on cast iron.

Also, the concentric channels are OK but you need to cut some radial channels as well so you don't get suction and sticking when you get to 9um or 5um. I prefer X,Y channels in a grid over concentric channels, but that's just personal preference.

Mike