Kitamura Mycenter 5X Tool Deflection BIG PLUS
Kitamura Mycenter 5X, 10,000 RPM, air/oil bearing lubrication, gear driven
Loss of preload contributing to further component damage
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 & 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.
We performed a grind, hard chrome plate & finish grind of the 100mm front housing bore & the Big-Plus 40 taper. We also kiss ground the taper face to complete the requalification of the tooling interface to Big-Plus factory spec. We reassembled the spindle with all new bearings, Belleville springs, grippers, drive dogs, o-rings & assembly screws. We set the proper bearing preload & test ran the spindle for six hours to break in the new bearing grease (especially critical with the rear roller bearing) while recording the thermal & vibration characteristics. Our final outgoing QC indicated, among other things, only 2µ runout in the tooling taper & on the face and a 50% increase in tool retention force. We also supplied, at the customer’s request, a new rotary union.