I built this as a wildly rough-n-ready proof-of-concept from stuff I had lying around my shop.
I wanted to see if the idea was worth pursuing.
Well, it WAS worth pursuing, and I've gotten most all of the engineering done on a production version:
I gotta get this thing finished up one of these days - but I've run into a seemingly intractable problem . . .
You see, I want it to be a 'dead man' foot pedal - you step on it to RELEASE the ball, and if your foot slips off, WHAM! It locks in place.
My current proof of concept will kill you if you let go of the vise/workpiece when the pedal is in the released position. That's bad form, old boy! Bad Form!
But... the problem is, it takes about 1000 pounds of force on the center of the toggle-clamp linkage to compress the spring enough to release the ball.
With about a 10:1 leverage applied on the foot-pedal lever, that's 100 pounds - easily done with one foot.
But... if your foot slips off, the PEDAL will fly back at the speed of sound (my terrified guess) and can whack your shin, splintering it into many little fragments!
No, this is not a statement from direct experience, it is an FMEA (failure mode event analysis) conclusion. But I am assured by my prior experiences with stored energy (with the scars to prove it!) that it's a predictable result.
So... my design sits on my shop floor, half finished, waiting my brain to kick in and cough up the answer.