What is bend allowance in sheet-metal fabrication?

Bend allowance is the arc length of the neutral axis through the bend region. It is commonly computed as BA = θ(rad) × (R + K × T), where θ is bend angle, R is inside radius, T is thickness, and K locates the neutral axis.

Why can finished parts still be off after using bend allowance?

Real parts vary with die opening, punch radius, grain direction, springback, and material lot. Production work usually applies shop-specific bend deduction tables from measured test bends rather than pure theoretical values.

Sheet Metal Bend Allowance Calculator

What K-factor should I start with?

A common starting range is 0.30 to 0.50 depending on material and tooling, with many mild-steel air-bend setups near 0.42 to 0.45. Use this tool for first-pass values, then calibrate against your brake and bend-test coupons.

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Use the Sheet Metal Bend Allowance Calculator to get an exact answer for your inputs.

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What K-factor should I start with?

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