Sheet Metal Bend Allowance Calculator

Inputs

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Degrees the flange turns from flat (90° = right-angle bend).
°
Inside bend radius (the radius the punch forms on the inside of the bend).
mm
Sheet thickness.
mm
Neutral-axis position; ~0.33 for air bending, up to ~0.45.

Results

Default result
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Bend allowance(BA)
5.749mm

Neutral-axis arc length through the bend.

Also computed

Bend deduction(BD)4.251mm

Subtract one per bend from the summed outside flanges to get the flat length.

Outside setback(OSSB)5mm

Method notes 2 notes
  • Flat (blank) length = sum of the outside flange lengths − one bend deduction per bend.
  • The K-factor places the neutral axis as a fraction of thickness; it is empirical and varies with material, tooling and bending method — verify it with a test bend.

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