Bend Allowance Calculator for press brake forming.
Enter the thickness, inside radius, angle and the sum of the outer flanges, and the calculator gives you the bend deduction and the length at which the part must be cut. A half-millimeter error over four bends puts the part outside assembly tolerance, and the correction is paid for in sheet metal already cut.
OSSB = (r + t) x tan(A/2)
BD = 2*OSSB - BA
L = sum of flanges - n * BD
From the outer flange sum of 300.0 mm, subtract 2 deductions of 3.48 mm, meaning 6.95 mm in total. Cut the part at 293.05 mm.
Limits of the calculation.
The K-factor is not universal
The default value of 0.44 is common for carbon steel at small radii. For stainless steel, aluminum, or large radii, the real factor differs and is determined on a test piece. The calculation is only as good as the factor entered.
Flanges are measured on the outside
The sum you enter must be the outer flange dimensions, meaning the drawing dimensions measured on the outer face. If you work with inside dimensions, convert them first.
Confirm on a test piece
Any serious shop validates the first part of each new item. The calculation reduces the number of trials from several to one, not to zero.
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