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

Q: 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.

Q: 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.

Question

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

Accepted Answer

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.

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

Answers