The picture that georgebarr posted is just one step shy of the ideal bearing support. It only has a set screw on one side. If you drill and tap all four sides you have what is a (very) basic 4 jaw chuck!
All your end plate alignment problems evaporate.
And, thinking about it for a moment, you could probably do something similar on the table drive plate too. Then radial adjustments of the nut as fine as frog hair are easy
.
robotic regards,
Tom