Bend deduction and K-factor explained simply

When sheet bends, the inside compresses and the outside stretches. The neutral line in between keeps its length.

The K-factor tells where the neutral line sits — usually 0.33 to 0.45 of the thickness from the inside.

Bend deduction is the amount you subtract from the outside flange lengths to get the flat blank. It depends on thickness, inside radius, die opening and material.

Test once on your own press brake with your own tools, record the value, and store it in your bending table. After that every unfold is accurate.