Its hard to put in words but easy for .5 k factor. So I’m going to go into depth, and I hope it helps someone. This is the best video I’ve found. When he says radius, he means radius plus k factor. K factor is almost always .4 to .5 for steel and aluminum. So he just took half of his material thickness being.( .5 = K factor). He then added that to the bend radius to get his “R” it’s really this!!!!!……….. material thickness x the K factor x 2 x pi x the angle of bend divided by 360 ……… that’s the equation if not an easy .5 k factor. (K factor changes on the type of metal you are bending) there are easy google charts if you know what you are bending. There are also calculators but learn this first!

I think that the figures calculated are with a neutral axis in the centre of the material so that the stretch and shrinkage are equal in this case . To make a more realistic bend allowance formula requires the formula BA= AxPi/180 x( R + KT ) Where BA = Bend Allowance A = angle of bend in degrees R = Internal radius of bend ( found from bending tool ) K = K Factor , which is found empirically ( By trial and error ) Or from Westinghouse tables T = Material thickness . So I think that this is a start to find the allowances but will be inaccurate as the K factor varies .

Circumference of what?

@@dart70ca Circumference of the circle on the neutral axis . So a 90 degree bend would be a quarter of the circumference of the circle , as 90 / 360 = 0.25 . I hope this clarifies it for you .

That works well for 90 deg bends but not as well for other angles.

Yeah that doesn’t work if you have quality control and tolerances. You need to actually do the math.

Scrolled down to the comments to ask who the hell Ross Gibbs is. You beat me to the punch, you Spanish bastard! Also, I heard a rumour that Kevin smells.

@@donorush Ross is from the engineering department and I actually had him for Statics and Mechanics of Materials. Great teacher but pulls no punches