This morning I had one of our operators call me over to look at a problem she was having on an old Mazak lathe. It is an old QT-15. Well, she had been running just fine when she shut the door and saw that the screen had gone blank. In addition, the spindle speed over ride had dropped to 000 and the indicator light for the tailstock showed that it was extended. First thing I did was push the reset button to clear everything. Crap, when I pushed the reset, the spindle came on and the turret indexed. At that point, I peed a little while scrambling for the E stop. I called our maintenance guy over. He reset the E stop, and opened the front of the controller, which caused the turret to index again. Ghost in the machine. After some examination, he discovered that a CNMG insert had somehow fallen into the electronics and lodged behind the circuit board. It was randomly shorting out, sending spurious commands, as if someone was randomly pushing buttons on the controller. Never saw that one before.
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