Tube bending formula

[smcadman]

I haven't been able to find a formula for bending square tubing. Typically we cut a few pieces until we get it right, but there has to be a way to calculate this without going through several stocks of tubing.

For example:
1" square cold-rolled steel tubing
45 degree bend
2 1/2" inside bend radius
leg 1 = 35"
leg 2 = 21 1/2"

Also, a formula for round tubing would be great also.

Flores

 

[ajack1]

Not sure about tube but for sheets I always start with

(2/5 thickness + inside rad) x 6.28 =360 degrees and then build in a factor for the material through experimentation, this gives the development for the bend.

So for the example you give

(2.90) x (6.28 / 8) = 2.46” so assuming the lengths of 21 ½ and 35 are flat lengths and not to intersection points the length would be 58.96”

This should give you somewhere to start and from there I would factor in any errors and see how different wall thickness etc change things through experimentation.

The more you refine the closer you will get.

Hope this helps.

 

[smcadman]

Thanks Ajack, but I was hoping someone had a formula for square tube. For sheetmetal bend dedcutions, I use Bendworks,

http://www.massey.ac.nz/~odiegel/bendworks/

But, because of the side walls in square tube, Bendworks isn't perfect. For 90 degree bends, a k-factor of .6035" seems to work pretty good, but I can't find a suitable k-factor that works for all angles.

Flores