Because you mentioned I just went to my workshop to check my spindles taper bearings http://malamuterun.co.uk/homemade_cnc_mill_spindle.htm
It was running for good 4 hours cutting a metal and spindle around bearing is hot. I did not break them in at all. Just wonder, are they heating up because they are submerged in oil (run @ 3000rpm) or because I didn't follow breaking procedure ??