Sheet Metal Bend Calculator

Metal stretches on the outside of a bend and compresses on the inside, and somewhere between the two sits a neutral axis that does neither. The K-factor says where — typically 0.33 to 0.5 of the thickness from the inside face — and it is why the flat blank is shorter than the sum of the legs. K-factor rises with bend radius and varies with material and forming method. 0.44 is a reasonable default for mild steel air-bent at a radius near one thickness; bottoming and coining push it higher, and the only reliable figure is one measured from a test bend on your own press. Bending below about one material thickness of inside radius cracks most steels on the outside of the bend, and aluminium alloys are worse — some temper designations need three or four times thickness. The grain direction matters too: bending across the rolling direction is far more forgiving than along it.