"DIF over" is a report back to you saying that the actual position of the axis is not the same as the programmed or calculated position and this error difference is over the permitted allowance.
As it is occuring on the Z-axis, check all on this axis, leadsrew, gibs tight in 1 spot, backlash, swarf build-up, ( stupid question- but are your drills sharp ? ) anything that may make the drive work harder, seeing it go to 105% makes me think the motor is OK, and the problem is either with the action on the slideways, leadscrew and/or bearings, or the action of the tool into the workpiece
When the macine is OFF, leadscrew should turn freely by hand.
does it occur with no tool being used ?
does it occur in other spots of the slide ?
does it occur using the manual handwheel or jogging ?
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