Kitamura Mycenter 3XiH Spindle Failure from lack of lubrication
Improper bearing lubrication, worn Big-Plus taper
Kitamura Mycenter 3XiH, 20000 RPM, oil injection bearing lubrication, gear drive
Prior to shipping this high speed vertical machining center spindle to us, our customer indicated that it was very noisy when operated above 12,000 RPM. When we disassembled the spindle, we noticed that the rear shaft nut was only finger tight. Even more telling was the heat discoloration evident on the inner spacers of not just the rear roller bearing, but also between the front quad set of angular contact bearings. This was indicative of improper lubrication which would have eventually led to catastrophic failure of all bearings. Fortunately, this did not occur, and the only dimensional deviation we found in our evaluation was in the tooling taper. Our customer uses both CAT & Big-Plus dual contact tooling, and we found that the Big-Plus tooling was contacting the shaft face before it was touching the taper itself.
We first performed a grind, chrome plate & finish grind of the worn tooling taper to Big-Plus specification. We then reassembled the spindle with all new bearings, o-rings, assembly screws & grippers, which we had found to have significant wear. We test ran the spindle while checking its thermal & vibration characteristics. When our customer reinstalled the spindle they initially experienced a slightly elevated operating temperature, but the spindle was producing a mirror finish. We reminded them that they should check the operation of their oil lubrication system, and subsequent adjustment by their dealer’s service personnel solved the heat issue.