Sheet Metal Bend Calculator
Calculate bend deduction (BD), bend allowance (BA), setback (OSSB), and flat pattern unfolding length for precision sheet metal fabrication.
Flat Pattern Length
96.74 mmBend Deduction (BD)3.26 mm
Bend Allowance (BA)3.74 mm
Setback (OSSB)3.5 mm
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Unfolded Dimensions
Formulas based on ISO 2768 / DIN 6935 standards for air bending and bottoming.
Method
How Sheet Metal Bend Deduction Works
When sheet metal is bent, the outer surface is stretched in tension while the inner surface is compressed. The neutral axis is the plane where no deformation occurs, characterized by the K-factor (ratio of neutral axis distance to thickness). Bend Deduction (BD = 2 × OSSB - BA) accounts for material stretch so your cut flat pattern produces the exact finished outer dimensions.
Send Size to Laser Quote →Frequently Asked Questions
What is K-Factor and how to choose it?
K-Factor represents the ratio of the neutral axis depth to the material thickness (t/T). Typical air bending values range from 0.38 to 0.45. Softer materials like aluminum usually have lower K-factors (0.40), while steels average around 0.44-0.45.
What is the difference between Bend Allowance (BA) and Bend Deduction (BD)?
Bend Allowance is the arc length along the neutral axis around the bend. Bend Deduction is the amount subtracted from the sum of the flange lengths (A + B) to find the flat blank length (L = A + B - BD).
Does this support acute and obtuse bend angles?
Yes, the calculator supports any bend angle from 1° to 179°, dynamically recalculating outer setback (OSSB) and bend allowance accordingly.