K Factor Calculator
Calculate sheet metal K-factor, neutral axis location, and bend allowance from material thickness, bend angle, and inner radius.
What Is a K-Factor Calculator?
A K-factor calculator finds the neutral axis position during sheet metal bending. Enter material thickness, inside bend radius, bend angle, and either bend allowance or K-factor to compute the other values used in press brake and fabrication planning.
How K-Factor Is Calculated
The K-factor is the ratio of neutral axis distance from the inner surface to material thickness:
$$ K = \frac{180 \cdot BA}{\pi \cdot \theta \cdot T} - \frac{R_i}{T} $$
Neutral axis location from the inner surface is:
$$ t = K \cdot T $$
Bend allowance can be recovered from K-factor using $BA = (\pi \cdot \theta \cdot T / 180) \times (K + R_i / T)$. Typical K-factors for sheet metal fall between 0.3 and 0.5 depending on material and tooling.
For angle conversions used in bend calculations, try the Angle Converter and Right Triangle Calculator.
Frequently Asked Questions
What is the neutral axis in sheet metal bending?
The neutral axis is the line inside the cross-section where stress is zero during bending. Material above it is compressed and material below it is in tension. Its position shifts with bend radius and material thickness.
What is bend allowance?
Bend allowance is the arc length along the neutral axis for a bend. It is added to flat pattern length so the finished part reaches the intended dimensions after forming.
What K-factor should I use for steel?
Many cold-rolled steel jobs use K-factors between 0.33 and 0.45 depending on inside radius to thickness ratio. Measure a test bend or use shop standards for best accuracy.
Can I calculate bend allowance from K-factor?
Yes. Switch calculation mode and enter thickness, inside radius, bend angle, and K-factor. The calculator returns bend allowance and neutral axis distance.
Does bend angle affect K-factor?
K-factor is often treated as a material and tooling property, but bend allowance always depends on bend angle. This calculator uses angle directly in both K-factor and bend allowance formulas.
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