Daewoo ACE V35 Even sealed bearings can fail (in part) from contamination
Daewoo ACE V35, 7000 RPM, grease lubrication, belt driven
Our customer indicated that they noticed vibration in this vertical machining center spindle during operation, and that the bearings felt gritty when the spindle was rotated by hand. We noted that the bearings were in fact very noisy and felt rough when rotated in assembly incoming. Upon disassembly we observed that the spindle interior was full of a black sludge. Despite having a complement of sealed bearings, this contaminant had washed out most of the grease and what was left was severely degraded. But there was another factor in the failure of this spindle, which turned up in our full dimensional evaluation of the major spindle components. The vibration our customer had noticed was due to the excessive wear and runout (>60µm) we measured on the pulley journal of the shaft. This condition in turn likely caused significant fretting damage to the 60mm rear bearing journal. We also noted that the #40 tooling taper ID and the tool retention gripper fingers were in relatively poor condition.
We completed a grind, chrome plate and finish grind of the pulley journal and the 60mm rear bearing journal. We also completed a single-pass kiss grind of the #40 tooling taper ID. After a thorough cleaning of all components, we rebuilt the spindle with all new bearings, Bellevilles, grippers, o-rings and assembly screws. We finished this rebuild with our final test run, break-in, trim balance and final QC, and the spindle is currently back in production and running like new again.