How this calculator works
The neutral layer follows an arc between the inner and outer sheet surfaces. K is the neutral-axis offset divided by thickness. Use the angle turned from a flat sheet, not the finished included angle. Bend deduction uses the two outside setback dimensions. The right K-factor comes from the material, tooling and bending process, ideally a measured bend coupon.
Formula
BA = theta (r + K t); outside setback = (r+t) tan(theta/2); BD = 2 setback - BA, theta in radians.
Worked example
For a 90 degree bend, r = 2 mm, t = 1 mm and K = 0.4, BA = 3.76991 mm and BD = 2.23009 mm.
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Frequently asked questions
Is bend angle the included angle?
Here it is rotation from flat: 0 degrees is flat and 90 degrees is a right-angle bend.
Can I assume K = 0.5?
That places the neutral layer halfway through the thickness. Real bending can move it, so verify the process.
What is bend deduction used for?
Subtract deduction from the sum of two outside flange dimensions to obtain the flat blank length for one bend.