@Spelljammer This is along the lines of what I was thinking for potential causes of the warping. I think the pivot point comment is particularly on the mark. It's hard to tell without seeing the designs; but I think part of the problem is that the position of the center point is in the middle of the thread - not actually at the mirror (front or back). This would change the distance from the lasby PaulP - Polar Machines, SCARA, Robot Arms