Art, when we began testing a new Buddie48 PRS for repeatability we used a dial indicator inverted under a centering point bit chucked in the spindle.
This confirmed that we could develop a few thou hysteresis if we used an XY move then Z up and down followed by an XY return and a Z up down. After a few cycled moves we found about 0.002-0.004" hysteresis in repeatability of the Z axis movements.
I thought that was just the motors and drivers loosing a fraction of a step of resolution over repeated operations?
What did you do, if you did finally resolve this matter, to solve your problem/question that lead to this thread?
cheers,
Kevin Morin