[Kwirk]

normally I prefer .012mm / 300mm (.0005" / 12" inches). If it is out more in X, than Y this would cause what you see.
Also with scales you cannot check backlash since the scale is trying to hold the axis in position.
This is NOT the case under a dynamic load when cutting!
You need to look at the ball-screws. (Procedure attached)
"_Troubleshooting_Axis_Positioning_Problems-VMC-110518GEW.pdf" (289.0 KB)

Thanks alot for taking your time

I havent checked the screws more then by feeling them byhand
And having a 0.002 dial gauge. They feel really nice.
The finishes it leaves during roughing and finishing are really nice. I cant even feel the slightest errors where it changes direction so focus on the screws has been minimal.

I have witnessed some sloppy screws on the scales machines and during machining you can easily feel the backlash on circles

I am thinking of stacking up some calibration gages of 300mm measure first in X with 3d taster. Then measure in Y direction ( first turn taster 90 degreees )
Im pretty sure the measurement will differ 0.02.

What would be the cause of this then?

[gwood]

The tests I provide instructions for on the end of the ball-screw take less than 15 minutes;
spend your time looking for bad thrust bearings; or ball-screws that have lost their preloads.