Milltronics VM20IL Spindle Repair

The Milltronics VM20IL is a high speed CNC machining center.  It can come fitted with either a 10,000 rpm or this 15,000 rpm we repaired.  The 15,000 rpm spindle is grease lubricated, coupling driven, and comes with ceramic ball bearings.

CHALLENGE

This Milltronics VM20IL spindle had bearings that were growling and felt rough when rotated by hand in assembly incoming.  After completing a full breakdown and evaluation,  we noted that the rear bearing pair had failed, the cages were destroyed and the debris from those had contaminated the front bearings as well.  The front bearings contained an excessive amount of grease which was significantly degraded.  We then measured critical dimensions (bearing journals, housing, taper, etc.) and found a few issues.  First, the tooling taper ID had damage at the mouth and extremely poor tool contact.  Second, the drive keys were heavily worn and will need to be replaced.  Lastly, the gripper fingers (collet) were damaged on critical tool retention surfaces.  No other dimensional deviations were noted for this repair.

SOLUTION

The following actions were performed on this Milltronics VM20IL spindle:

• Clean, inspect overall dimensions
• Grind, chrome plate, and finish grind the tooling taper ID
• Replace ceramic bearings, bellevilles, grippers, drive keys, o-rings, and assembly screws

RESULT

After reassembly of all components, adjusting bearing preload, and undergoing break-in and testing procedures, this spindle passed our final quality inspection before being returned to our customer with a 1-year warranty.