Kira VTC40B Spindle Repair

The Kira VTC-40B is a production CNC vertical machining center with CAT40 tooling.  It comes standard with a grease lubricated and dircet coupling driven spindle capable of running up to 8,000 rpm.

CHALLENGE

Our customer indicated that this vertical turning center spindle had become very hot and had overloaded the motor. After it cooled off, they noticed that the spindle felt very rough when rotated by hand.

When we evaluated the spindle, it was apparent that the front quad set of bearings had failed due to coolant contamination. The front of the spindle was packed with a sludge of coolant and washed-out grease, and the races, balls & cage of the rear-most bearing in the front set had actually started to separate due to the increased friction and lack of lubrication. We also observed very low drawbar retention force due to compression of the Belleville springs. Our dimensional inspection showed that the ID of the rear bearing housing was looser than ISO spec, but there was no fretting on either the housing ID or the outer races of the rear bearing pair. We reported our findings to the customer, but did not recommend a grind, chrome plate & regrind of this component because it did not contribute to the spindle failure.

SOLUTION

The following actions were performed on this Kira VTC40B spindle:

• Clean all parts of the spindle
• Replace all bolts, o-rings, and bellevilles
• Replace collet gripper balls
• Replace bearings

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.