Turns out that the bearings are moving in the blocks. I'll have to try our local bearing supplier tomorrow and see if they have some of these: Shim/Support Washer 20mm x 28mm x 0.3mm DIN 988. If not, I'll have to get the blocks skimmed to reduce the depth of the bore.

I'm really pleased with the ballscrews and machining from Chai but these bearing blocks are shyte. Have I got some from a bad batch or is this "normal"? I guess this clarifies why John S told me he doesn't use the BK or BF bearing blocks!

While on the subject, which way round should the 7001 AC bearings go in the blocks?