FlatBend: Sheet Metal Unfold

FlatBend is a fast, precise flat-pattern (blank length) calculator for sheet metal workers. It runs fully offline, is a one-time purchase, and has no ads or tracking.

WHAT IT DOES
- Single-bend quick calc: from thickness, inside bend radius, bend angle and K-factor, see bend allowance (BA), bend deduction (BD), outside setback (OSSB) and neutral radius instantly.
- Multi-bend flat pattern: lay out flanges (outside mold-line lengths) and each bend to get the total flat length automatically (Σ outside − Σ BD).
- Reverse solve: fix the flat length and solve one unknown flange.
- K-factor: presets 0.33 / 0.40 / 0.446 / 0.50, or an auto estimate from R/T (air-bend guide). Manual measured values are welcome too.
- Units: mm and inch, with fraction display (1/16, 1/32, 1/64).
- Angle: switch between bend angle and included angle.
- History: name, save and reload jobs, each with a bend-profile diagram.

METHOD
Neutral radius = R + K*T
Bend allowance BA = (pi/180)*A*(R + K*T)
Outside setback OSSB = (R + T)*tan(A/2)
Bend deduction BD = 2*OSSB - BA
Flat length = sum of outside flange lengths - sum of BD per bend

NOTE
Results are geometric estimates (K-factor method). K-factor varies with material, process and tooling. For precision, enter the measured K-factor from a test bend.