Kitamura Mycenter 5X Spindle Repair

The Kitamura Mycenter 5X is a CNC vertical machining center.  It comes equipped with an air/oil bearing lubricated and gear driven spindle capable of running up to 10,000rpm.

CHALLENGE

Prior to the arrival of this Big-Plus capable spindle, our customer indicated to us that the tool was deflecting radially during cuts. Our first observation prior to disassembly was that the spindle shaft had >60µ of axial movement (endplay.) We determined that this loss of bearing preload was due to a hydraulic nut which had been positioned (with the locking nut in place) so that it was not contacting the inner race of the rear-most bearing of the front quad set. Another result of this condition was that the 100mm front housing bore was fretted oversized +7/+25µ (ISO = ±7.5µ) in four bands where the unloaded bearings were located.

We also noted that the Big-Plus 40 taper & face were worn with excessive runout up to 6µ & 5µ, respectively. The tool retention grippers and the drive dogs were also heavily worn, and the incoming tool retention force was significantly lower than it should be. The front housing cover had some obvious dents, but these were purely cosmetic & would not have impaired spindle function in any way.

SOLUTION

We performed a grind, hard chrome plate, and finish grind of the 100mm front housing bore and the Big-Plus 40 taper. We also kiss ground the taper face to complete the re-qualification of the tooling interface to Big-Plus factory spec. We reassembled the spindle with all new bearings, belleville springs, grippers, drive dogs, o-rings, and assembly screws. We also supplied, at the customer’s request, a new rotary union.

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.