Yesterday I had a small aluminium piece about 1" in diameter, like a small cylinder head, and I needed to clean up and lightly polish the end after parting. The whole part was only about 3/4" in length so it was barely sticking out of the chuck at all.
I successfully took a light facing cut and proceeded to begin sanding it with some wet and dry at about 600 RPM (the speed the lathe was set to for the facing operation). I was cautious of the chuck jaws and tried to make sure I was using only light pressure and staying to the bottom of the piece.
It turns out I wasn't cautious enough and I'm guessing I strayed above the centreline of the part, which generates different forces on the wet and dry and requires different counterforces from the operator. I didn't have time to realise my mistake before the part grabbed the paper and threw my pointer finger into the 4 jaw chuck. The end of my finger jammed nicely between two of the jaws and in 1/20th of a second had twisted 180 degrees around the chuck, taking my hand/wrist to their maximum twist angle as well, then luckily ejected it into my chest, still attached to rest of me, although a little sore from it's adventure.
The ending was pure luck and could just as easily have ended with me only being able to count to nine. I know it was my fault, and I know exactly what I did wrong (nearly everything in this case) but I thought I'd write it up as a warning for others to listen closely to that little voice in your head that says "Don't do it, it's dangerous, you're being stupid". I got away with it this time but it scared the heck out of me...