Bend Deduction Calculator
When sheet metal bends, the flat length it needs changes. This works out the bend allowance and the bend deduction, so a flat pattern can be laid out from the finished dimensions.
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- Works offline after your first visit
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How it works
The bend allowance is the arc length along the middle of the metal: the angle in radians times the inside radius plus the K-factor times the thickness. The K-factor sits between 0 and 0.5 and depends on the material and the tooling.
The bend deduction is twice the outside setback minus the bend allowance. The setback is the radius plus the thickness, times the tangent of half the bend angle.
Worked example
For 0.125 in material bent to 90 degrees over a 0.25 in inside radius, the bend deduction is 0.271 in.
Questions
What is a K-factor?
It places the neutral line within the thickness, as a fraction. Shops often start near 0.44 and adjust it from test bends on their own tooling.
Why subtract the bend allowance?
The two outside dimensions run past the bend, so the flat length is shorter than their sum. The deduction is the amount that overlap removes.
Does this include springback?
No. Springback changes the final angle and is a separate correction, usually found by test bends.
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