I am talking about a sheet metal bender. Sometimes called a 'brake'. Bending metal of 1mm thickness or less. For those who don't know that's merely a long horizontal hinged metal bed upon which another sheet of metal is laid and clamped down just short of the hinge. Then closing the hinge forces the metal to bend at the clamp. If I take a piece of such metal say 1" wide, 6" long (and 1mm thick) and put one end in a vice leaving say 4" ( 100mm for convenience in measuring) sticking out I can attach a spring scale to the free end and pull on it while watching the scale. I note that the metal bends at 2kg of force applied. Continue that same 2kg and I can bend the metal down 90 degrees. So I am thinking that if I had a piece of that same metal 4' long then the force required to bend it would be 48 x 2kg = 96kg. And this is not an extraordinary force. And at the clamp there's no more than 2kg applied at each inch. It all sounds very simple and ordinary. But I am told that constructing such a device would require very strong construction indeed and that the force at the clamp would easily distort the clamp and cause a poor bend. That trying to bend heavier metal - say 2mm - would be sufficient to break the device, even the great heavy ones such as that found in my local hardware store for instance. Hinges snap off. The clamp breaks. So my understanding of the forces is obviously totally wrong. How are they to be understood?