Why do brake settings change with bend length?

[Deezl Smoke]

Let me preface this with,.....I am aware of the k-factor formulas and I am learning how to properly use them as time rolls on. In those formulas, the length of bend is included. I do understand that part. I use 3 point air bending here, no coining or bottoming etc. However...........

My mind works on a very basic almost child like manner. Most things are on or off, up or down etc. So when I have a brake that has a physical stop for the Y axis (depth of bend) why does length of bend matter? That,...is my question.

Let's say I want to bend a piece of 10g A36 mild to a 90* and install the proper die. If I use a scrap piece say 12" wide and set up a perfect 90* bend, (this is by trial/error, not formula based) and then put a 10' piece in to bend, I can't get but about 83*, maybe 85* if I'm lucky. Why??? Again, this brake has a physical stop on the ram for depth of bend. It is not based on digital input. 10g A36 wont begin to tax the press. So again, why? does the length of bend matter? It must have something to do with the metal's overall mass? It's not crown. It has to be something with the amount of steel in the bend. But can someone please explain this to me? I have an overwhelming need to understand the "why?" in formulas etc. For whatever reason I have never been able to just trust something as right without knowing the "why".

Thank you for any help or ideas.

[plasmanewbie]

I'm a pretty simple guy myself and you obviously have more experience with this than me however my guess would be flex in the machine. It would take more pressure to bend a much longer piece which may cause the machine to flex further reducing your bend angle. That's all i can think of.

[Deezl Smoke]

Ok. That does make sense. No matter how strong one might think the machine is built, there is a lot of power put in a very small location. I know if one does not anchor the brake to the floor, and does a fair bit of production work, the brake can actually walk around on the floor.

[Thor]

Yeah, flex of the upper and lower rams. Even though mine are like 2" thick and something like 3' tall each they still flex. That is why bigger better brakes have crowning adjustment. With that you can put an upward bend in the lower die to make up the difference of the flex. Without crowning and an air bending setup if you try and bend a long length you typically end up with a canoe shape.

You also have to be aware of your brakes max tonnage per inch. There are formulas to figure this out, but basically its a max number that if exceeded on a short length risks permanently bending the rams.

[adbuch]

Great information here! Although my press brake is much smaller, the same principles still apply.
Thanks,
David