Some time ago I worked in a repair shop. We fixed lots of machines which included wood lathes and the chucks to go with them. One day, one of the other technicians, who's english isn't too good, was going to check the runout of a wood chuck and he asked me how to do it. Just so happened I was going to check out a wood lathe which just happen to have the right kind of threaded spindle. Well, I had him clean the mounting surfaces and mount the chuck onto the spindle of that lathe (I'd already checked the runout of the spindle and it was within a few tenths). Had him mount a drill blank into the chuck and I clamped a dial indicator onto the tool post mount and without further fanfare turned on the machine. Just at that point I realized that the lathe was set to its highest speed, which was too sinking fast and without thought, turned the switch back off. Well, the lathe spindle stopped almost immediately, but the chuck didn't. And soon it was slamming against a wall in the shop and then over to the work bench whence it came and then back to the wall. Of course there were two bystanders who happened to be in the way and one of them is screaming at the other in Vietnamese about how the other's house should catch on fire, who's dog should be run over and who was going to suffer a broken nose as soon as he could stop dancing... not understanding a word, I made my escape as soon as it was prudent...