In my case, just like Gerry's reply, I was missing steps and pulled my hair out trying to find the culprit. Machine 2.5D all day,but would randomly skip steps on 3D stuff and you coud not hear when or where it happened. Playing with settings didn't do any good.
So I replaced the steppers with ones of  two and half times  the original torque rating, got rid of the backlash in X and Y axis by replacing  the bearings and adjusting the ball screw nuts, and life is good again. Now if i would only get off my lazy butt and redo the Z axis life would be really good on the mill.
RICH

I  have slowed the z axis way down and reversed the settings as someone else suggested.  It is much more accurate now.  I am making a gun stock.   Lots and lots of Z movement. It always worked O.K.  if I finished using the long axis X,  but when I finished using the Y axis going the short distance back and fourth across the material there is a lot more z movement

Thanks
JR

Hi,

I had a similar situation - Z axis would "drift away" after many moves.
Eg. after test case with 500 runs of subroutine that moves 10mm up+down, zero position would consistently be arround 4 mm to low. That makes arround 0.004 error per move (less than one microstep in my setup which is 0.0125mm).
Anyway, after I tried/checked all that was suggested in this thread, finaly changing the kernel speed from 35kHz to 25kHz made it work perfectly.
HTH

I am already at the 25kHz It is close but still after 25,000+ lines it is about .1in off not bad on wood I can fix most of that with sandpaper.

Thanks
JR

JR,

Do you get lost steps on any other axis or is it just the Z ?

Tweakie.

Just the z.