Calculate bend deduction from sheet thickness, inside radius, K-factor and bend angle, then use it to determine flat pattern length from finished outside dimensions.
Outside dimensions are measured from the theoretical outside apex of the bend to each flange end.
Enter your bend information and calculate.
Bend allowance (BA) is the amount of material along the neutral axis that forms the bend.
Bend deduction (BD) lets you work backward from outside flange dimensions to the flat blank length.
For a simple two-flange bend:
What is bend deduction? Bend deduction is the value subtracted from the sum of the outside flange dimensions to obtain the flat developed length.
What is bend allowance? Bend allowance is the developed arc length through the bend, normally calculated along the neutral axis.
Does K-factor affect bend deduction? Yes. K-factor determines the neutral-axis location and therefore affects bend allowance and the resulting bend deduction.
Why is the outside setback important? Outside setback determines the distance from the bend's outside apex to the tangent point of each flange.
Can I use this for any bend angle? The mathematical calculation supports bend angles from greater than 0° through 360°, but practical sheet-metal bend conventions and tooling geometry should be considered for unusual angles.
Can this replace a sheet-metal CAD system? No. It is a calculation aid for simple bend geometry. Complex multi-bend parts require a validated flat-pattern method.