Then, why do you wish I didn't use a rotating ballnut on the shorter axis? Has my choice caused you bother in some way?

My recollection is that you said it was overkill. It's not your job to tell me if I'm making a bad choice but I also don't expect 'I told you so' comments when I'm struggling to get it all working.

I think I know what the issue is anyway. On the ballnut mount I didn't have those massive retaining nuts on the shaft tightened up very much. That means when it pulls on the shaft the pulley inside the mount rubs. Does that make sense? However if I tighten the nuts on the end of the shaft to keep it in place, the shaft then rubs on the body of the mount since the two bearings are not perfectly parallel. I think I need to put a tiny spacer in there.

For those who don't know what I'm talking about, here is a picture of the mount.