The K-factor calculator finds the real K-factor of your material from one test bend. Enter the flat strip length, the measured flanges, thickness, inside radius and angle; it returns the K-factor, Y-factor, bend allowance and bend deduction to use in CAD and in flat pattern calculations.
Bend a test strip once, measure it, and enter the numbers below.
Use this K-factor in the flat length calculator or your CAD sheet metal settings. Questions about tooling? Ask our press brake engineers.
Formula
From the measured part, the bend deduction is the difference between the flange lengths and the flat blank. The bend allowance follows from the outside setback, and the K-factor from the bend allowance:
When flanges are measured on the inside, the inside setback tan(A/2) × R replaces tan(A/2) × (R + T).
How to bend a test strip
- Laser cut a strip of the production material at a known length, for example 100 mm × 50 mm wide. Write down the exact cut length.
- Bend it to 90° in the middle with the same punch, die and machine you will use in production.
- Measure both flanges from the outside with a caliper, and measure the inside radius with a radius gauge.
- Enter the values. Repeat for each material, thickness and die combination and keep a table.
What K-factor values to expect
| Bending method | Typical K-factor |
|---|---|
| Air bending, R about equal to T | 0.38 – 0.45 |
| Air bending, large radius (R over 3T) | 0.45 – 0.50 |
| Bottom bending | 0.38 – 0.42 |
| Coining | 0.30 – 0.38 |
A result outside 0 to 0.5 usually means a measurement error: check the flat length, whether flanges were measured to the outside or inside, and the bend angle.
Frequently asked questions
What is a K-factor in sheet metal?
It is the position of the neutral axis, the layer that neither stretches nor compresses during bending, expressed as a fraction of thickness from the inside surface. A K-factor of 0.5 means the neutral axis is in the middle of the sheet.
Why measure K instead of using a table value?
The K-factor depends on material batch, grain direction, die opening and the machine. A measured value removes the guesswork and keeps flat patterns accurate to a few tenths of a millimeter.
What is the Y-factor?
Some CAD systems use a Y-factor instead of a K-factor. It equals K × π / 2. For a K-factor of 0.44 the Y-factor is about 0.69.