Any change in OD will have to be wear in the slideways, you have to go up to tool room (Moriseki etc) lathes to get them not to cut a taper.
Marc the round columns have a problem stayng on centre when the head is raised or lowered. If it cuts on the backcut the head isn't straight.
Hi Lozza thanks for the tips, I will have to try the bar test at some point and take some measurements. But as long as I can hold a couple of hundredths over 300mm that will be good enough for bike axles and more than good for spacers.
Interesting my step father bought Chinese drill press for $100, fitted precision bearings and tuned it to make a mill for his model train parts ..... it is accurate enough to within a few microns at the drill chuck, so a lot can be achieved in the set up..... plus ditching the bearings in anything from China and Korea is a step forward.
