Sheet Metal Bend Deduction & Allowance Calculator

Precision flat pattern unfolding calculations for sheet metal forming and press brakes.

Sheet Metal Thickness T (mm):

Inside Bend Radius R (mm):

Bend Angle (degrees, e.g. 90):

K-Factor (default 0.33 to 0.45):

Result

BD = 3.55 mm

BA: 3.49 mm | OSSB: 3.52 mm (90° bend, T=2.0mm, R=1.5mm)

Methodology & Formulas

BA = (π/180) × Angle × (R + K × T)
BD = 2 × tan(Angle/2) × (R + T) - BA

When bending sheet metal on a press brake, the material on the outside undergoes tensile stretching while the inner radius compresses. Accurate bend deduction ensures precise dimensional tolerance in CAD flat patterns.