I was having problems with the Y axis binding and back lash. After some work I figured out the lead screw was bent or not concentric. You could see the far end move almost 1/8” as it turned. This was with both the stock retainer and my home made bearing block. If you tightened down the acme nut the axis would bind, bad.

I finally ordered a replacement lead screw and nut, 20 tpi from LMS. I went to put them in and the opposite end also moves as it rotates but less than 1/2 what the original one did. So I play around and finally get some compromise where the acme nut is tight in its mount and the stepper does not stall BUT the whole table rocks as it turns! If I tighten the jibs down enough to take that movement out the stepper stalls.

So the problem still seams to be the lead screw and bearing surfaces are not concentric. Is this a common problem? I have done some google searching but have not seen any direct complaints about this machine. Is there some way to design a bearing mount to compensate for the problem with out increasing back lash? Maybe find some one with a lathe that would let me true up the shaft and then buy new bearings and pulley?
Y axis rocking - YouTube

Thank you.