Work out the flat blank length for a sheet metal part. Enter the thickness, inside bend radius, bend angle and material (which sets the K-factor), and the calculator returns bend allowance, bend deduction, outside setback and the flat length by both the allowance and deduction methods.
What it gives you
- Bend allowance from the K-factor neutral axis position
- Bend deduction and outside setback
- Flat length by the bend allowance and bend deduction methods
- Neutral axis offset for the chosen material
- Bend allowance versus angle table for the current material
Method and standards
Bend allowance is the arc length of the neutral axis through the bend: BA = (π/180) A (R + K T). Bend deduction is twice the outside setback minus the allowance, where the setback is tan(A/2)(R + T). K-factor depends on material, tooling and bend ratio, so the values here are typical starting points; confirm with a test bend for close-tolerance work.
How to use it
- Enter thickness, inside radius and bend angle.
- Pick the material, or type a K-factor from your press brake data.
- Enter the leg lengths to get the flat blank.
Questions engineers ask
- Which K-factor should I use?
- Around 0.33 for tight bends and 0.44 to 0.50 for radii larger than the thickness are typical for mild steel and aluminium. Your own press brake tests are more reliable than any table.
- Metric and imperial?
- Yes. Both unit systems are supported.
- What about hemming and multiple bends?
- Calculate each bend separately and sum the flat lengths. Hems need their own allowance.
Need this calculation done properly, with a signed-off calculation pack or FEA behind it? Forgepoint provides mechanical design, analysis and pressure equipment engineering from Manchester, UK-wide.
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