How much force does it take to bend 3”x16ga box tube to a 5’ radius in one pass? What’s the largest steel shape you can jam in a typical scene shop-built manual roll bender without cracking a roller? A week ago I didn’t know the answer to either one of these questions, now I’ve got a pretty good idea.
We’re talking about making a roll bender at work, and are waffling over whether to build a manual or motorized bender. I realized that we didn’t really have a handle on the forces involved in bending various steels to various radii; these numbers are instrumental when making this decision. (Not to mention during the design process.) Earlier this week I sat down and created an excel file to shed some light on the situation. Figured I might as well share it with my peoples.
Snag the files here: XLS or PDF
The majority of the worksheet calculates for:
- The force required to bend a variety of steel shapes to various radii in one pass (à la motorized bender).
- Adjustments for three different roller/die distances: 12”, 16” & 20” apart.
The manual pass sections are intended to show how much force would be needed when making the first pass in a manual roll bender. It calculates:
- The force required to reach the yield point of each steel shape.
- The resultant deflection and radius achieved in the first pass.
- The above calculations adjusted for three roller/die distances (12”, 16” & 20”).
Big effin disclaimer! Lets be honest folks, I’m not an engineer. Confidentially (just between you and me) I am confident that the calculations are fairly accurate. But under no circumstances will I claim that they are 100% accurate. The reason is this: the last thing I need is a lawsuit because someone too lazy to verify the math took it in the eye from a flying bit of steel. Don’t you dare cut corners.
This worksheet is only intended to give a general idea of the numbers involved when bending steel. It cannot be counted on to give precise data concerning specing and designing of a specific machine. There are no allowances for the inherent springy-ness of mild steel, dodgy steel quality and varying manufacturing tolerances.
Bending steel is indeed a fudgy art. But now you’ve got some numbers.