I think I have backlash, I was having some problems using my mill as a lathe with a cut off tool on some brass and starting measuring things. A test indicator was put into the spindle, I brought the Z axis down to the vise until the needle moved, then zero the indicator dial and the DRO. holding the control key and stepping .001 it takes exactly 5 button pushes to move down .005 (this would be continuing down from a previous downward motion). Then when I start pushing the page up key the first push has no physical movement but you can hear the motor turn. It takes 6 pushes .006 to move the .005 distance back up to zero, then it takes another 6 pushes to get back down to .005 because again the first .001 of the direction reversal does nothing.
So, that sucks, how do I fix this? would it be the ball nut loose on the screw? or is it the thrust bearings on the end of the ball screw? At any rate the gibs are tight enough to allow this to happen otherwise there would be no backlash at all if the head was hanging from the screw like a bowling ball hanging from a rope (not that I am suggesting that as a fix only as an observation of current function).