I ordered a set of ball screws and linear bearings from Chai. When they arrived the box was badly damaged at one end. I took photos of the damage before opening. The ends of two rails were bent. I mailed Chai and he said that the cost of shipping was prohibitive for replacement. If I placed another order for whatever I didn't need, he'd happily slip in a replacement. I cleaned the ends up on my mill and ground the linear bearing ends so they are now nice and pretty (previously it looked like they were cut off with a chop saw).

Roll on several months and I build my z-axis. Installed the ball screw etc. and when rotated the re-circulating bearing oscillates up and down. I initially suspected that the screw was bent, but after much fiddling I concluded that the screw was not turned centrally when the shoulder was machined for the fixed bearing mounts. This is because even with the ball re-circulator at the fixed bearing end, it still oscillated by the same amount as when it was in the centre. If the screw was bent I would expect the movement to diminish as the bearing reached the extremes of travel (think plucked guitar string).

As this was discovered six months after delivery, rather than get into a discussion (argument?) with Chai, I priced up a replacement (~£19 delivered). I have fastened the ball screw down with as near as damn it half the error to try and minimise the forces placed on the screw (this makes it have stiff-spots when rotating). It is not brilliant, but I will try it on the machine and then decide to throw more money in Chai's direction. I am a couple of months away from having power on the z-axis so this decision is deferred.

Even with the less-than-brilliant experience as described above, the price is a small fraction of parts sourced in the UK (Moore International etc). I wanted to buy British, but it just doesn't make sense as I would have spent ~£1500 more on the basic drive parts.

Neil.