I've got a 3020T and it seems fine apart from a problem with the y axis which seems to come on after the mill has been running for a while. It stalls like if you have set the feed rate too high and looses track of where it is, i.e. end up being short of where it should have got to. I've taken a video of it, this was the worst it has ever been at this point.

http://www.readresearch.co.uk/person...l_stalling.avi

I've got the motor and coupling close and centralised OK, the y axis is tighter than the others, but this is to be expected as it's got more weight to carry and a longer leadscrew? Also has a tiny bit of eccentricity.

Any ideas? I'm wondering if it's the control box.