OK, thanks for all the advice! Have now dismantled the machine and
- Good news, ballscrew seems to be ok
- Not so bad news, looks like the problem was one of the bearings on the ballscrew ends. Specifically the "fixed end" with dual bearings has a crunchy bearing which looks extremely worn (wobbles significantly with finger pressure)

Some photos of the busted bearing here. You can see that one side of the bearing is heavily worn:
https://www.dropbox.com/s/4o3jqujyoy...53.23.jpg?dl=0
https://www.dropbox.com/s/63o33g6d96...53.36.jpg?dl=0

Now this machine is not setup ideally.
On the motor side is
- Single bearing 26x10x8mm (OD x ID x width), labelled 6000Z
On the opposite (to motor) side is the dual bearing, each is:
- 22x10x6mm, labelled 6900Z

The bearing housings are literally just holes cut in the aluminium chassis plates (reasonably accurately drilled, bearings are a tight fit). On the motor side the bearing fits from the outer side. On the dual bearing end there is a hole each side of the frame, so the machine frame is between each bearing (I guess you could describe the mount as an I shape with the bearings each side of the I). There is a large nut applying clamping force to the outside end of the ballscrew (dual bearing end) and I think no washers.

So working backwards.
- I think I need to replace the dual bearings with angular contact type?
- Google finds me these: http://www.wychbearings.co.uk/71900-...C5-Enduro.html
- Any comments about price, alternatives, suppliers?
- I guess I need to understand and check the mounting arrangement for these? My limited understanding would be to arrange the bearings back to back, such that they are being clamped together by the two ends of the ballscrew? However, I would need to check that the machine frame isn't touching the inner race (which looks like it was in the photo above, causing a bunch of wear due to the inner race being ground between the outer nut and inner frame mount)?
- What kind of torque levels should be applied to the AC bearings? Keep increasing until there is no measured backlash?

- I'm also planning to change the larger motor side bearing (since it has evidence of damage on the oil seal). I believe this should be a deep groove bearing? Any thoughts on suppliers? I plan to add a wavy spring washer to tension it, but still allow for some machine movement? Perhaps another angular contact bearing would be better though? (machine is aluminium framed)


I also observe that the linear bearing carriages are quite stiff to move. I'm unclear on how smooth these linear carriages should be though...? I will post something separately once I have the bearings replaced, however, any thoughts in the meantime appreciated. Note I have no idea if the carriages (hiwin) are already greased. There is nothing left after the wipers from the track move past. There is a bunch of chatter from the balls. It does have grease nipples already fitted (unlike the ballscrew...), any thoughts on what to lube with (uncovered linear rails, so dust is a problem, prefer to use dry/non sticky lubes where feasible)

Thanks!

Ed W