Quote Originally Posted by 109jb View Post
This is because my ballnut setup uses springs to force the ballnuts apart resulting in absolutely no backlash. The spring force is about 100-150 pounds driving them apart. On most double nut setups the ballnuts have shims between them to provide as little backlash as possible without binding, but because of screw lead errors the shimming cannot eliminate the backlash without binding the screw at some locations, so this method usually still has a little bit of backlash. Not much, but still a bit..
Yep. I have a tiny bit of binding in places (minimal) after shimming. I've got down to 0.01mm on X and 0.025mm on Y. Near enough. I've gone a bit mad with 1100oz steppers which should cope. If anything the nuts will eat themselves before I have step problems

All this has made me strip the column again for the 4th time. Decided to rip out that crap DFU I just put in in have a go at getting my 2 single nut mashing design right. Took 0.13mm worth of shimming to get it to loosen off from where I had it. Seems to run smooth by hand now and looks like there is about 1 degree of free area. With any luck I'll be within a backlash of 0.03mm.