The bearings in this grinding spindle were very noisy when the spindle was rotated by hand incoming. During breakdown, it was noticed that the rear bearings would slide on & off the rear shaft journal by hand. The journal was undersized by nearly twice ISO, a condition which if left uncorrected would lead to premature bearing failure. Our dimensional evaluation also revealed excessive runout on the drive pulley taper OD, tooling pilot face & the front bearing shoulder. The customer did not provide their drive pulley, but from the rub out & signs of heat on the pulley taper, it appeared that there was poor contact between the pulley ID & taper OD. The customer did provide us with a quill which afforded us an opportunity to confirm that the 4µ runout on the pilot face was significant, translating to 52µ runout on the ID taper of the quill when installed in the pilot.
We remedied the dimensional issues by performing a grind, chrome plate & finish grind of the rear bearing journal as well as a kiss grind of the drive pulley taper OD, tooling pilot face and the front bearing shoulder. The only parts to replace during reassembly were the front & rear bearings. We test ran & balanced the rebuilt spindle while confirming the vibration & thermal characteristics before returning it to our customer.