I met a guy on another forum who had a really nice mill, but no vise. He claimed it was in storage, and just needed it for a little project. My wife had an emergency so I was running out so I just gave him the vise and told him I'd get to his shop later. I explicitly gave him a 6" box end wrench and told him to only use that for tightening the jaws...
2 hours later I got to his shop. horrors. He had removed my hardened and ground in place jaws. He was using a 2-4-6 block to tighten on the bottom of a rotary table and was trying to take a full milling pass of 1.5" 7" above the jaws of the vise (if you can't imagine it, think the piece is 8" high and was taking a 1.5" cut along the top edge.
- of course the part was moving, and messing up the cast iron where the real jaws seat to. In addition, he was using a socket and a 20" Johnson bar to try to clamp down on the soft cast iron. - So the lead screw nut is ruined, the jaws won't seat any more, and his job was a mess.
I clamped it properly, finished his job and took the ruined vise home. I haven't had the heart to rebuild it, yet. I bought a new vise to do work on in the mean time. Of course, loaning tools to this jerk will never be an option again.