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Engineering calculator

Bend Deduction Calculator

Calculate the deduction for a sheet-metal bend and convert outside flange dimensions into flat pattern length.

Calculate Bend Deduction

Enter thickness, finished inside radius, angle and K-factor. Results update as you type. The starting values are an example.

mm

mm

deg

K is dimensionless. Use a value between 0 and 0.5 calibrated for your material, tooling and bending process.

Optional: calculate flat pattern length

Enter both outside flange lengths, measured from each free edge to the virtual intersection of the outer faces. Each must be at least the outside setback.

mm

mm

Bend deduction, BD

--

Subtract BD from the sum of outside flange lengths.

Per bend

Bend allowance, BA
--
Outside setback, OSSB
--
Flat pattern length, L
--

Enter both optional flange lengths to calculate L.

Preparing calculation.

Bend deduction formula

BD = 2 × OSSB − BA

OSSB = (R + T) × tan(θ / 2)

BA = (θ × π / 180) × (R + K × T)

T is material thickness, R is the finished inside bend radius and K is the neutral-axis depth divided by thickness. θ is the angle bent from flat in degrees. Use degree mode for tan(θ / 2); the calculator converts degrees to radians internally.

If you know the inside included angle α, use θ = 180° − α. A right-angle bend is 90° under either definition.

Reference: SOLIDWORKS bend deduction

Calculate flat pattern length

L = A + B − BD

A and B are outside flange lengths to the virtual sharp. Do not substitute the straight lengths to the bend tangencies. For those measurements, use L = a + b + BA in the bend allowance calculator.

Example: T = 2 mm, R = 2 mm, θ = 90° and K = 0.42 give BA ≈ 4.461 mm, OSSB = 4 mm and BD ≈ 3.539 mm. With outside flanges A = B = 50 mm, the flat length is approximately 96.461 mm.

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