Hardinge VMC 1500XP3 Spindle failed rotary union



CHALLENGE

Contaminated bearings, leaking rotary union Hardinge VMC 1500XP3, 8000 RPM, grease bearing lubrication, pulley driven This vertical machining center spindle arrived completely disassembled, but it was readily apparent that a leaking rotary union had allowed coolant contamination to penetrate the entire spindle interior. Not only were the rear cover & drive pulley heavily corroded, but the grease was mostly washed out of the rear roller bearing and the front quad set of angular contact bearings, plus the drawbar assembly was full of sticky coolant residue as well. When we tested the tool retention force, it was 1300 lbs compared to a minimum spec of 1900 lbs. The light wear we observed on the gripper (collet) fingers may have contributed to this. We also measured runout of 30-40µ at the end of a 9” test bar.

SOLUTION

To alleviate the excessive runout, we performed a kiss grind of the tooling taper in-house on one of our Kellenberger grinding machines. We then reassembled the spindle with all new bearings, Bellevilles, o-rings & assembly screws. Our customer opted not to have us install new grippers because they already had a set in good condition left over from a previously-replaced drawbar assembly. We test ran the spindle for 4 hours to break in the new grease while closely monitoring the vibration & thermal characteristics. When our customer received the rebuilt spindle, their 3rd party CNC service technician installed a new rotary union and the replacement gripper set. The rebuilt spindle is now making chips and performing flawlessly.

DETAILED CAUSE OF FAILURE

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