Re: Encoders
If you want tight tolerance then I would keep the servos and put 1 micron magnetic linear encoders on the axes, on table and the z axis. That gives you 25400 counts/ inch. Cost about $120 per axis for magnetic encoders. You need a real industrial motion controller and mating software. I use Galil motion controllers, and my own software. My software is not for sale, but I do give it away for free.
Mach 3 would not be my first choice for controllers. For one thing, encoders are useless on Mach3, it has no way to read them. Mach3 is open loop only. I don't know anything about UCCNC.
I've upgraded a few machines, and the last one I did for a guy will hold single digit micron accuracy consistently. It was a nice tight machine. My mill will hold +/- 0.0001 (+/- ~2 microns) in all axes if I need it to.
Jim Dawson
Sandy, Oregon, USA