Stuart, yes many thanks, Google got me there as well, but their 4 mm rollers are either too short at 4mm or too long at 11.8 so I decided to use the originals.
So onwards and upwards! I removed the vertical and horizontal thrust races. The Horizontal one has 80 solid 4 mm rollers all of which were ok measurement wise so they went back as is.
The vertical one on which the weight of the table and work is taken comprises 36 hollow rollers of 8 mm diameter, one of which was broken
![:bang:](https://madmodder.net/Smileys/default/BangHead.gif)
However I now think that this was why the table was jamming. I was surprised to find they not only were hollow, but had really quite thin walls. I've come across hollow rollers in bearings before in for instance the Gamet headstock bearings of a Colchester Student, but they were quite thick walled. So what to do?
Options - a/ Leave a roller out b/ Try and source one c/ Make one. I opted for c/ on the grounds that although it probably would be perfectly ok leaving one out, it's not very professional, and I was unlikely to be able to find just the right roller. I turned a piece of silver steel to just oversize in the hard state using carbide tooling, then lapped to size. I decided to leave it solid as no doubt the flexibility of the steel would be totally different to the original.
So here we have the broken roller with it's replacement, and the bearing back in situ: