Bending calculator

Bend Deduction Calculator

Calculate sheet metal bend deduction and outside setback from bend angle, inside radius, thickness, and K-factor to size a flat pattern from outside flange dimensions.

Calculator inputs

Results update as you type. Switch units at any time without changing the physical values.

Set all

Use Fabworks production values

Choose stocked material to load its production bend radius, calibrated K-factor, thickness, and production tool setup.

Only catalog combinations with measured bend calibration are shown.

Stock thickness
0.032 in
Production inside radius
1 mm (0.0394 in)
Calibrated K-factor
0.373
Production tooling
1 mm (0.0394 in) punch nose · 8 mm (0.3150 in) V-die

Fabworks tooling keeps its native metric callout. For air bending, the V-die opening and material response also affect the finished radius, so the preset pairs that radius with the K-factor calibrated for the complete production setup.

Upload a STEP file to Fabworks and we detect the bends, apply the production setup, and calculate the flat pattern for you.

The angle through which the material is bent.

Neutral-axis position as a fraction of thickness.

Results

Bend allowance
0.1024 in
Outside setback
0.1 in
Bend deduction
0.0976 in

Quick answer

How this bend deduction calculator works

Bend deduction is the length you subtract from the sum of the two outside flange dimensions to get the flat length. It equals two outside setbacks minus the bend allowance, so it depends on bend angle, inside radius, thickness, and K-factor.

How to use the calculator

  1. 1Enter the bend angle (how far the flange turns from flat, 90° for an L-bracket), material thickness, and inside bend radius.
  2. 2Enter a K-factor, or choose a Fabworks material preset to use measured production values.
  3. 3Add the outside flange dimensions from your drawing and subtract the bend deduction once per bend.
  4. 4For production parts, confirm the flat pattern against the material and tooling that will form the part.

Worked example

90-degree bracket from outside dimensions

Inputs
Two 1.000 in outside flanges, angle 90°, inside radius 0.040 in, thickness 0.060 in, and K-factor 0.42.
Result
Bend deduction = 0.0976 in; flat length = 1.000 + 1.000 − 0.0976 = 1.9024 in.

Each outside setback is 0.100 in and the bend allowance is 0.1024 in, so the bend deduction is 2 × 0.100 − 0.1024.

Common questions

What to know before using the result

When should I use bend deduction instead of bend allowance?
Use bend deduction when your drawing gives outside flange dimensions. Use bend allowance when you add up tangent (straight) lengths and the arc length of each bend.
Does bend deduction change with material?
Yes. Thickness, inside radius, and K-factor all change it, and those depend on the material, temper, and tooling used to form the bend.
Do I need to calculate bend deduction for a Fabworks order?
No. Upload a STEP file of the bent part and Fabworks unfolds it with the material and tooling that will form it. The calculator helps when you design from a drawing or check a flat pattern.

Formula

BA = θ × (R + K × T)

The bend angle θ is converted to radians. R is inside radius, T is thickness, and K locates the neutral axis through the material thickness.

Engineering references

Assumptions and limits

  • The bend has a constant inside radius and thickness.
  • Fabworks presets use measured production calibration; generic K-factors remain estimates.
  • Bend deduction uses two equal outside setbacks.
Educational estimate
Use this result for learning and early design exploration. Verify safety-critical or production decisions with the governing standard, material data, real tooling, and a qualified engineer.

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