Y axis problem

[Neale]

If you are using a dti to measure travel, you should be able to measure backlash, if any, and eliminate that as a cause. Set up the dti so that it is at mid-travel, then move the axis a couple of mm in one direction and return to starting position. Note dti. Then do the same in the opposite direction. Difference in dti readings is a reasonable estimate of backlash. Could be as simple as badly-adjusted ballscrew angular contact bearings.

If the error were rather smaller (of the order of 0.005mm) but increased by the same amount each time you repeated the movement, I would suspect a step pulse polarity problem. I'm a bit sensitive to this one as it bit me in the bum on my machine, and it's a bit subtle to detect as it doesn't show up very easily except after many repeated direction changes. However, your error is many times larger - which is why I asked exactly how you were doing your test. Over what distance, at what speed, does the error show up after one movement or after many repeats, etc. If you can fill in the details, it might let someone spot a likely problem and/or eliminate red herrings.