Bend Deduction Calculator
If you’re operating a CNC Press Brake, or in general if you calculate the changes to material length caused by adding bends, this calculator will do that for Steel, Aluminum or Stainless. Just enter your material, angle, inside radius, and thickness. The diagram and readouts update live. K-factor can be entered directly (most accurate) or estimated from the material and radius-to-thickness ratio as a starting point to confirm with a test bend.
Inputs
Cut Length
Pick your part shape, type the finished length of each side (measured to the corner, the way it is dimensioned on your drawing), and get the length to cut the flat blank before bending. The bend settings above (angle, radius, thickness, K) decide how much is removed at each fold.
Both bends in a U-Bend use the same angle, radius, and K set above. For a part that mixes different bends, work it out one bend at a time.
How it is calculated
With bend angle A (degrees bent through), inside radius R,
thickness T, and K-factor K:
- Neutral-axis radius:
Rn = R + K×T - Bend Allowance (neutral-axis arc length):
BA = (π/180) × A × Rn - Outside Setback (tangent point to virtual sharp apex):
OSSB = tan(A/2) × (R + T) - Bend Deduction:
BD = 2×OSSB − BA - Flat length:
L = Σ(mold-line flanges) − (bends × BD)
The neutral axis is the layer that neither stretches nor compresses during forming.
K places it as a fraction of thickness, measured from the inside face. Bend deduction is
the amount the flat blank is shorter than the summed mold-line dimensions, because the sharp theoretical
corner contains more length than the actual rounded, stretched bend.
On K-factor accuracy: K is empirical. It shifts with material, temper, tooling (punch radius, die width), and bend method. The published default of about 0.44 traces to low-carbon steel air bent over a conventional V-die. Soft aluminum at a tight radius can run nearer 0.33. Use the estimate to lay out a test bend, measure the result, then back-calculate K from the real part for production layout.
Geometry is exact for the inputs given. K-factor values are empirical starting points, not certified results. Verify with a test bend before committing material.
