I’m waiting for the parts to break in (I may need to polish the ends of the screws where they meet the helical couplers), but the preliminary results are in. After fashioning some parts and putting the X axis on my retrofitted mill back together, the results are quite a bit better than they were initially. I’ve now got double ballnuts on the X axis, along with zero backlash helical couplers.

1/1000 of backlash on the X axis. I don’t actually have the helical coupler screwed in because the initial fit was so tight, so it is possible that it’s causing a wee bit of slip (I doubt it though). 1/1000 is way better than the initial 7.5/1000 that I was getting before though. Later this week I will write a CNC program to run the axis back and forth a couple hundred times…then I’ll recheck the thrust bearings and measure backlash again.