Miyano BNC-34C Axial and Radial Movement in the spindle shaft


Our customer’s lathe spindle arrived covered in dried coolant residue. Coolant contamination had completely washed out the grease from the front pair of angular contact bearings and the rear roller bearing. At some point the rear bearing cage had disintegrated, spilling the rolling elements into the spindle housing and distributing a fine black powder throughout the spindle interior. Needless to say, the front pair fared no better. Now provided with freedom of radial & axial movement, the spindle shaft rubbed out on the front labyrinth. We also noted severe wear on the timing pulley, in the tooling pilot & on the shaft face. Although there was light fretting on the shaft from the bearings once the lubrication had disappeared, there were no significant dimensional deviations found on the shaft journals or in the housing bores.


We first performed a kiss grind on the shaft face to alleviate the excess runout, and we machined out the rubout damage to the front labyrinth. We replaced the bearings, o-rings and assembly hardware. Our customer declined our recommendations to replace the timing pulley and to grind, chrome plate and finish grind the shaft tooling pilot. According to our standard break-in procedure, we ran in this spindle at progressively increasing speeds for a total of eight hours while checking the vibration signature & thermal signature and shipped it to our customer within three business days as an expedited repair.


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