Calculator Inputs
Three columns on large screens, two on tablets, one on mobile.Plotly Graph
The chart compares bend allowance, bend deduction, and flat length across your selected angle range.
Formula Used
1) Neutral axis radius: Rn = R + K × T
2) Bend allowance: BA = θ × (R + K × T), where θ is the bend angle in radians.
3) Outside setback: OSSB = tan(θ ÷ 2) × (R + T)
4) Bend deduction: BD = 2 × OSSB − BA
5) Flat length for one bend: Flat Length = A + B − BD
6) Reverse K factor from measured bend allowance: K = ((BA ÷ θ) − R) ÷ T
Keep all dimensional inputs in the same unit system. K factor is dimensionless.
How to Use This Calculator
- Choose whether you already know the K factor or want to solve it from a measured bend allowance.
- Enter thickness, inside radius, bend angle, and both flange lengths.
- Provide either the K factor or the measured bend allowance, depending on your chosen mode.
- Select quantity and graph range if you want a broader angle study.
- Press Calculate to show the results above the form and refresh the graph.
- Use the export buttons to save the calculation as CSV or PDF.
Example Data Table
| Thickness | Inside Radius | Angle | K Factor | Bend Allowance | Bend Deduction | Flat Length |
|---|---|---|---|---|---|---|
| 1.20 mm | 1.50 mm | 45° | 0.33 | 1.489 mm | 0.748 mm | 79.252 mm |
| 1.20 mm | 1.50 mm | 90° | 0.33 | 2.978 mm | 2.422 mm | 77.578 mm |
| 1.20 mm | 1.50 mm | 135° | 0.33 | 4.467 mm | 8.569 mm | 71.431 mm |
FAQs
1. What does K factor represent?
K factor shows where the neutral axis sits through the sheet thickness during bending. It links material stretch behavior to bend allowance and flat-pattern accuracy.
2. Why is K factor usually between 0 and 0.5?
The neutral axis normally stays between the inside face and the sheet midpoint. That makes most practical K factors fall between 0 and 0.5, though unusual inputs can solve outside that band.
3. When should I use reverse mode?
Use reverse mode when you already measured bend allowance from a test coupon or proven shop part. It helps derive a K factor that matches your actual tool, material, and process behavior.
4. Does the calculator support inches and millimeters?
Yes. You may work in either unit, but every dimensional value must use the same unit system. The calculator preserves consistency rather than converting mixed units automatically.
5. What is bend deduction used for?
Bend deduction converts flange dimensions into a flat blank size. It is especially useful when drawings are dimensioned to mold lines or outside dimensions instead of direct flat lengths.
6. Why do larger bend angles reduce flat length?
As bend angle rises, bend deduction often grows faster than the straight flange sum changes. That means the developed flat length can shrink for the same flange inputs.
7. Can I use this for production estimates?
Yes, for quick estimating and planning. For release-level manufacturing, confirm results with shop standards, tooling data, material grade, grain direction, and at least one physical bend test.
8. Is this only for one bend?
This page models one bend between two flanges. Multi-bend parts can be handled by repeating the calculation for each bend and summing the relevant developed sections carefully.