I am not a young student. I'm an old man with rotten physics and maths.

My plan is to build a sheet metal folder. This kind of thing:

https://www.kincrome.com.au/metal-bender-730mm
Just like a hinge you lay the sheet metal on, across the hinge bit, and then close the hinge up which forces the metal to bend.

I need to know how strong to make the various parts. There's not many, a top clamp and the bending leaf and the hinges at each side is about it.

Those are the places that will fail if I get it wrong.

So I've learned that mild steel has a Yield Tension strength of about 250MPa

So I guess that force must be applied by the bending leaf to the job at the hinging point.

And one should be able to work out what force must be used to lift the folding leaf given its size and what the forces will be on the hinges and therefore how strong they must be and what force on the clamping bar...

BUT: I don't know how to do it.

To show I'm trying I'll set out what I've figured so far, such as it is:

mild steel sheet metal Yield Tension Strength 250MPa.

Use 1mm thick sheet metal for convenience (pretty real, too).

Use 1 metre wide sheet of metal.

Use flap of metal on the folding side of 1m long.

So we've got a moving flap of metal 1m x 1m.

So the cross sectional area of the bend is 1mm x 1m = 0.001mē

So 256MPa = 256M Newton/mē

So I need 0.001 x 256M Newtons = 256K Newtons.

I think that's the force that will need to be exerted at the bend and that force will bear back on the hinges of which there's only two.

So the hinges will bear 128K Newtons each.

Now 1 kg weight = 10 Newtons.

So this is like 12.8 K kilograms each.

That's fantastic. That's like 12.8 tonnes on each hinge.

So that's me stymied. I reckon that's got to be wrong but I don't know how to make it right.

And when I consider the whole hinge thing I can't understand it as a lever. Where is the fulcrum? At the bend it must be? Or where?

And so on.

I would really like some help.

There's plenty of help, tables and formula on the web for press brakes - that is bending machines that bend sheet metal by hitting it with a die.

But I can't find anything about this. Yet this seems the most basic and primitive. A real starting point.