Jonathan,

wrt spindle: evidently you have read the manual for my lathe more recently than me, I have no reason to question the MT4!! Thank you for correcting me :-) I am sure I would have worked that out at some point when I draw up the spindle :-)

my grandiose ideas of using 5 AC precision bearings as per SKF recommendations: I think now are more likely to be tapered rollers as you suggested - they are much tougher and 2 of them should be just fine.

wrt cross slide: putting ballnut at the rear of the slide seems a bit ugly but tis a workable solution, a driven ballnut would be nicer, but I can't find anything appropriate.

wrt motor: As I said, the gearbox has too much slop in it for it to stay for live axis use, I am looking to invest in an Servo to drive the spindle, something slightly smaller (this is a 36Kg motor!!) than http://www.ebay.co.uk/itm/REXROTH-IN...#ht_959wt_1071 :-)

With a 1:2 drive:spindle ratio that would give me 9K RPM :-) I don't see any issue with low speed using a servo motor.

Clearly the inertia ratio here is overkill and I don't want to blow that much on it but I have time for hunting.

cheers,

Jon