Thanks to Zapp and Kip for the information.

I've machined the ballscrew as per KIps drawing and fitted the BK BF as Zapp's instruction and all is well. In fact all is so well that I went on a building binge last week and especially the weekend and almost finished the mechanicals. X,Y and Z axes are near as dammit complete so look out for some piccies soon. I say almost finished because Marchant-Dice still haven't delivered my Rack and Pinions after three weeks, they now say TNT lost them and they are having the manufacturer send them direct, I thought MD WERE the manufacturer! Only the second time I've dealt with them and never again. I only went with them because Zapp don't do rack (hint, hint).

Anyway.....

I had originally intended to buld the gantry from heavy PVC plate but I think I was heading down a dead end street. I couldn't see how I would get the stiffness I needed given the forces invloved. I therefore decided as I work in the local forge (as they call it here), I should make the base frame and gantry from steel box section. The gantry ends are still PVC as are the Y and Z tables and it has worked out better than I could have imagined. The marriage of the two materials has worked really well. The Z is driven by one of Zapp's ready made 16mm ballscrews and the Y by a 25mm ballscrew (machined by me, first time ever on a lathe YAY!!!). The X is driven by rack and pinion, both sides (if it ever gets here).

Cutting area is 1250mm x 800mm x 120mm in the Z (I intend installing a 4th axis as soon as funds allow).

I'll post some pictures later for your critical gaze....

regards to all