Leg vise from junk

[Toolmaker51]

Agreed, Drew1966. I don't recall leg vises that weren't associated with blacksmithing. Mechanically speaking, that seems to counter best possible grip on parts; of jaws engaged flat on material. I've considered fabricating a leg vise over the years, with a notched link versus hinge. Tuomas's compression springs are a great solution.

With some bit of a thread hack;
Mentoring potential machinists, getting to discussions on machinery setup, I rely on a quick demonstration of leverage. Sketching it out is not effective. Some few decades now, the ability to grasp simple, unalterable principals has waned.

"Put your index fingers flat on the table, about this far apart [using a wood pencil]".
I lay pencil across their fingers and thumb the middle. Then I move thumb closer to one of their fingers, and press the same amount.
"So what position of the clamping stud is going to hold more securely?"
They get it every time.
Having them arrive at concept the strap must pinch at the end or be flat, takes a little more convincing.