Free Engineering Tool

Bend Allowance & Bend Deduction Calculator

Compute the flat pattern length of bent sheet metal parts using bend allowance, bend deduction and K-factor for air bending and bottoming. Supports L and U shapes plus K-factor reverse calculation.

1 · Mode

2 · Material & K-Factor

K-factor (0….5 typical)

Air bending: mild steel 0.33 · stainless 0.35 · aluminium 0.33. Bottoming: add 0.05….10.

Sheet Thickness t

Inside Radius R

Bend Angle α

3 · Shape & Flange Lengths (to bend intersection)

Leg 1

Leg 2

Measure flange lengths to the bend intersection (mold line), not to the outside of the bend.

Flat Pattern Length

75.75 mm50 + 30 −BD = 75.75 mm

Bend Allowance BA

5.75 mmneutral-axis arc through the bend

Bend Deduction BD4.25 mm2×OSSB −BA

Outside Setback OSSB5 mm(R + t) × tan(α/2)

K-factor used0.33neutral axis / t

V-die suggestionV-die opening ≤?16 mm8T rule

Geometry within recommended limits for this material.

Geometric values only …"springback is not modelled. Confirm with a first-article bend; typical overbend compensation is 2…° for mild steel, 5–0° for stainless and 5…° for aluminium. See DIN 6935, ISO 7438 and Machinery's Handbook.

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