How To Calculate Forces In A Sheet Metal Bender?

I want to build myself a sheet metal bender.

That is an instrument with a hinged flat bed we lay a sheet of metal on, clamp it down near the hinge and then lift the movable side thereby making the metal bend at that point.

I would like to know the force required and therefore the force experienced in the jaws of the thing and therefore how strong I have to build it.

The plan is to be able to bend up to 4 foot wide and metal up to 1mm thick. Mild steel.

My researching has taught me a bit and I've come up with formula for bending by a die forcing metal down into a V and for a die forcing metal down over the corner of a block. They're both pretty similar.

A constant multiplied by the length of the bend multiplied by the thickness of the metal (squared in one instance) multiplied by the tensile strength of the material and divided by the gap length in the case of the 'V'.

So I get the idea but I don't get it well enough to be able to figure out the formula for the simple bender I'm thinking of.

And I seem to have exhausted google's resources... can't find anything more with better information. A bit surprising really because I'd think this kind of bender would be the ubiquitous, most common and basic, etc... But the info I find is much more about big machine shop die presses and stuff..

Can anyone help ?