Eric, I've never been able to find any advice on preload for taper roller bearings. All I ever do is to run the machine (lathe, in my case) for 15 minutes at a fairly high speed to warm it up, then feel round the bearings to make sure things aren't heating up too much before I start adjusting. Then I tighten the adjusting nuts while rotating the spindle manually until a bit of additional drag is apparent. Next, I back off about an eighth of a turn (which is around 5 thou on my 1mm pitch adjusting nuts), lock the nuts up, and run for another 15 minutes. If another temperature check shows that, while warmer than before, things are no hotter than a comfortably drinkable cup of tea, that seems to work. At least, it works for me (famous last words!).
A finger inside the spindle to feel around the inside of the bearings can be better than feeling round the outside, where the mass of metal conducts heat away more rapidly. Unplug the machine first, because fingers don't screw back on too well. And make sure there's someone within calling distance, if there's any chance of getting your finger stuck.
Andy
