I have about .006" lost motion in my "Y" axis on my knee mill and that is the best I can get it. I have taken everything apart and cleaned and readjusted my gibs and checked everything with an indicator but I can't get it any better than that. How can I use the cnc control to account for the lost motion?
There has to be a mechanical source that can be fixed. 0.006" is really more backlash than you want to try to compensate for in software.
Have you checked for axial freeplay in the screw, indicating that the thrust bearings are not secure or (less likely) worn out?
Have you verified that the yoke holding the ballnut is secure?
Can you feel the backlash when you turn the pulley back and forth by hand with power removed?
If you really want to try software lash compensation, it is on the Machine Configuration -> Motor Parameters table:
1) Press F1/Setup
2) Press F3/Config
3) Enter the configuration password (default is "137")
4) Press F2/Machine
5) Press F2/Motor
6) Arrow over and down to the Y axis lash comp value
7) Enter the desired compensation amount
8) Press F10/Save
9) Press ESC three times to return to the main screen.
If you have newer software (since perhaps 2003?) you can also access the lash comp amounts from the Utility screen: F7/Utility, F6/User Maint.