It your choice; but I would bet it is mechanical alignments, or leveling.
I believe you..just running out of ideas.
I did now measure with 0.0001" dial and the out of round is
0.0127 per side so a diameter in X is 284.00m and in Y
283.9873mm
The smaller it get the better it is.
Would a tram error do this ?
Would tram error result a square to be smaller in one direction too ?
I will borrow a level and check the machine when i have time for it![]()