Thanks very much Lee, that is all very useful, I will go down that route for supporting the leadscrews. But that isn't what I was after! I was concerned about leadscrew movement in the direction of the axis- what you might call -fore and aft' movement rather than 'side to side'- as the leadscrew begins to turn, what stops it moving a short distance twoards the stepper motor (or away)? On my lathe there are thrust bearings to prevent that movement.
Thanks again
Richard