Homebrew stud extractor

The most important thing on installing cotter pins is that they are tight and don't wiggle in the hole or twist because it could eventually causse them to wear.

John

A chain wrench, strap wrench, oil filter wrench, pipe wrench, vise-grips as in the picture, etc., are made to work well in one direction.

I'm thinking of motorcycle front drum brakes, which evolved to dual-leading shoe designs with two cams, lifting the leading edges of both shoes. And then, they had very little stopping power when rolling backward, which didn't matter anyway. They worked significantly better in one direction.

I snap the stud, absolutely.

Maybe he could have hammered the stud over into an L shape, and then got a crescent wrench on it.

Many of the wrenches you've described -- in fact all but vice-grips -- are indeed designed so that turning in the "right" direction makes them grip substantially tighter. Not true of vice-grips, and really doesn't look true of a nut in a clamp (in this case the clamp is the vice-grips, of course).

Not familiar with motorcycle brakes -- but with automotive brakes, the brake cylinder pushes the top of both shoes, and the friction of the front shoe against the drum ends up pushing the bottom of the rear shoe. It also works substantially better forward than reverse, but that's not because of any wedging.

That would be awfully crude! Easier to get a nice shiny finish cutting it off flush with an angle grinder, and if you were careful, wouldn't ding the threads, either.

Use vise-grips the wrong direction, and they practically fall right off the fastener and pop open. At least, mine do. Look at the movable jaw in the picture posted. Turn the tool the correct way (left) and the jaw is wedged closed, tightening around the nut. Turn the wrong way, and the jaw is forced open.

the vice-grips,

The nut in this homebrew stud extractor isn't in a clamp, it's the clamp. It's an extension of the jaws, part of the tool.

And if the nut _still_ turns on the stud, some lapping compound on the threads could gain the extra bit of friction to make it work.