Sheet Metal Flat Blank Length Calculator

How to use the calculator

Measure each leg from the outside surface to the virtual sharp, the point where the two outside surfaces would meet if the bend were sharp. Add the legs together and enter the total. Set thickness, inside radius and the bend angle as the deflection from flat, so an L-bracket is 90. If all bends match, set the number of bends and the calculator subtracts one bend deduction per bend. Read the flat blank length from the primary result and use the sweep chart to see how sensitive the length is to your K-factor assumption.

Worked example and common mistakes

A 2 mm steel bracket with 100 mm and 60 mm outside legs, a 2 mm inside radius and K of 0.33 gives BA = 1.5708 x (2 + 0.66) = 4.18 mm. Setback is 4 mm, so BD = 8 - 4.18 = 3.82 mm and the flat length is 160 - 3.82 = 156.18 mm. Common errors are measuring legs to the tangent line instead of the virtual sharp, entering the included angle instead of the deflection, and assuming one K-factor suits every material, tool and radius.

• Use the deflection angle, not the included angle
• Measure legs to the virtual sharp
• Validate K-factor with a sample bend