Bridgeport VMC 3020 Spindle Repair

The Bridgeport VMC 3020 is a high production vertical machining center.  It is equipped with a belt driven, grease lubricated spindle capable of 10,000 rpm.

CHALLENGE

This spindle arrived at our facility after being completely disassembled by another rebuilder. Our customer told us that he had become frustrated when the quote was not provided for nearly a month. After consulting with the OEM, the customer decided to get the spindle into our hands for re-quoting.

In these cases it is never a simple task determining the cause of failure, especially when the spindle has significant damage to multiple components. The ID of the front hydraulic nut was worn to the point of being unable to grip on the spindle shaft, which allowed the front bearings to lose preload. The rear roller bearing had also suffered catastrophic failure. In both cases, the bearing journals and shoulders of the spindle shaft had also been damaged. In addition, the tooling taper of the shaft had excessive runout and one of the drive dog mounting screw holes was severely damaged. Finally, it was determined that the drawbar shaft was bent and twisted by >170µ, and the spring seating washer was missing.

SOLUTION

Our usual comprehensive approach to spindle rebuilding would have made this repair cost-prohibitive, especially since our customer uses this machine for secondary operations. They asked us if we could find a way to provide a more economical repair while still offering our one year warranty. We were able to repair the front hydraulic nut by grinding, chrome plating, and finish grinding the ID. The spindle shaft, drawbar shaft and spring seating washer were replaced with used components which we had recertified to fall within spec. We used all new components to replace the front bearings, rear roller, bellevilles, gripper balls, seals, o-rings, and assembly screws. We even upgraded the rear roller from a brass cage as found to a version with a phenolic cage which has a higher speed rating more appropriate to the top rated speed of this machine.

RESULT

This spindle passed our final quality inspection before being returned to our customer with a 1-year warranty. Our customer reported to us that they have run multiple jobs and the spindle has performed as expected. They also expressed their appreciation for our responsiveness, quick turn-around and our ability to tailor a successful solution to their particular circumstances.