K-Factor Calculator

When sheet metal undergoes a bend, the inner surface experiences compression while the outer surface undergoes tension. Between these two zones lies the neutral axis—a layer within the metal that neither stretches nor compresses. The K-factor represents the ratio of the distance of this neutral axis from the inside bend surface (t) to the total material thickness (T). The primary equation used is: K-factor = (180 * Bend Allowance) / (π * Bend Angle * Material Thickness) - (Inside Radius / Material Thickness). Additionally, the exact physical location of the neutral axis from the inner surface can be found using: Neutral Axis Location = K-factor * Material Thickness.

Imagine you are working on a custom fabrication project where a piece of sheet metal requires a specific bend. Let us plug the following values into our formulas: Bend Allowance = 15 mm, Bend Angle = 60 degrees, Material Thickness = 10 mm, and Inside Radius = 10 mm. First, calculate the K-factor: multiply 180 by the bend allowance (180 * 15 = 2700). Next, multiply pi by the bend angle and material thickness (π * 60 * 10 ≈ 1884.96). Divide 2700 by 1884.96 to get roughly 1.432. Finally, subtract the ratio of inside radius to thickness (10 / 10 = 1), yielding a K-factor of 0.432. To find the neutral axis location, multiply this K-factor by the material thickness (0.432 * 10 mm), resulting in 4.32 mm from the inside surface.

Always verify your material's temper and grain direction, as these physical properties can slightly alter the actual K-factor compared to theoretical calculations. Standard structural steels often default to a K-factor of around 0.33 to 0.50, but precise measurements on scrap test bends will yield the highest accuracy for tight tolerance work. Ensure your units of measurement—whether millimeters or inches—remain entirely consistent across every input field to avoid catastrophic scaling errors.