Just spent some time playing with a dial indicator on my Z axis. Run the axis up to zero, then using the Inc jog buttons, back it up. Strange thing- back the axis up .001", but it "jumps" about .004". Jog back the other way, it jumps again, back to zero. Only does this on the first button push each way, I.E. only when changing direction. Each successive move in either direction moves .oo1" as it should. This might say something about my drift issue. I wonder what the problem is- obviously not backlash as that would cause it not to reverse at all, especially not that small of a move. Maybe a gib too tight? "Stick-ion?"
Hmmmm, I'm making progress.