hi CES,
you are gving the answeres by yourselve

the ball screw with a spider coupler ($15 from Amazon)

you ae talking (dreaming) about 0.005 (doe's not mater if it is imperial or metric) with a rubber loaded Spider coupler (ok that is only one part of the dream).

ok again 0.005 (doe's not mater if it is imperial or metric) some "ideas"

-machine air condituioed?
-spindles rolled/grinded
-stepper Motors with Feedback (angle error??)


your Tuning expiriances 9999 or 10000 say everything.
sorry i have sayed this.

Tom