BA = bend allowance (mm)
Sheet-metal bend allowance
Neutral-axis arc-length estimate for one bend, using radians for angle.
FORMULA REFERENCE
BA = θ(R + Kt)
Neutral-axis arc-length estimate for one bend, using radians for angle.
Variables and units
Keep each value in the units shown below before substituting it into the displayed relation. Convert first rather than mixing unit systems inside one calculation.
θ = bend angle (rad)
R = inside radius (mm)
K = approved K-factor
t = thickness (mm)
WORKED EXAMPLE
Calculate the stated condition, then interpret its boundary.
Known values
- θ = 90° = π/2 rad
- R = 3 mm
- K = 0.33
- t = 2 mm
Substitution: BA = (π/2)(3 + 0.33 × 2)
Calculated result: BA = 5.75 mm
Engineering interpretation: Use a K-factor established by a bend test for the actual material, tooling and process; this is a preliminary allowance.
Conditions, limitations and review
- K-factor is based on actual material/tooling/bend condition
- Preliminary flat development only
Use this formula to understand or screen the stated engineering condition. A final design requires the governing standard, actual loads, material condition, manufacturing features and professional engineering judgement.
Source: J. G. Bralla, Handbook of Manufacturing Processes; approved shop bend-test data controls final blanks.