Bend Allowance Formula
The bend allowance formula gives the developed neutral-axis arc length through one sheet-metal bend. Use it with measured K-factor and tooling data before committing a flat pattern.
bend allowance formula bend allowance formula inside radius k-factor sheet metal bend allowance formula
Formula
BA = theta * (R + K * t)
Symbols
- theta: bend angle in radians.
- R: inside bend radius.
- K: neutral-axis factor for the material and tooling setup.
- t: sheet thickness.
Flat-pattern follow-up
Bend allowance is the neutral-axis method. If the drawing uses outside flange dimensions, convert with bend deduction: BD = 2 * OSSB - BA.
Frequently asked questions
Is bend allowance the same as bend deduction?
No. Bend allowance is added along neutral-axis flats. Bend deduction is subtracted from outside flange dimensions.
Should K-factor come from a chart?
Use a chart only as a starting value. Production flat patterns should use a measured K-factor from the actual material and tooling.
Related pages
- Sheet-metal K-factor calculator - back-solve K from a measured bend allowance or coupon.
- Bend allowance calculator - use a known K-factor to calculate bend allowance.
- Bend deduction calculator - convert between outside dimensions and flat length.
- What is K-factor? - neutral-axis explanation and formula context.
- Bend allowance chart - chart-style reference for the same live calculator.