Sheet-Metal Flat Pattern
One bend is arithmetic — that is what Sheet-Metal Bend is for. Four bends is where it goes wrong, and the number that goes wrong is not the blank length, it is where the bend lines land on it. That is what the operator sets the backgauge to, and it is not the running total of your leg dimensions.
Legs are outside mold-line dimensions — to the theoretical sharp corner, the way a drawing normally dimensions a formed part, and the convention the bend-deduction formula assumes. Blank = Σ legs − Σ deductions; the bend lines come from walking the blank, taking a setback off each leg and laying the bend allowance in between.
Material and tooling
The part, leg by leg
Each row is a leg and the bend that follows it. The last leg has no bend after it.
| # | Leg (mm) | Bend angle (°) | Radius (mm) | Direction |
|---|
Set the backgauge to
| Bend | Angle | Bend allowance | Deduction | Tangent at | Bend line | Tangent to |
|---|
Geometry with one K-factor for every bend. Real K varies with material, thickness, radius and tooling, and springback is not modelled at all — prove it on a test bend before you cut a hundred. It does not check bend relief, hole-to-bend distance, tooling interference or the order the bends have to be made in. The air-bending force uses F = C·UTS·T²·L/V with C between about 1.33 and 1.6 depending on whose friction allowance you take. A helper, not a substitute for engineering judgment.