Normals on an extruded surface

given an 5-subset extruded surface, exported via .3ds to vvvv for visualization,
i get a strange lighting effect that seems due to “bad” normals
can someone recommend a missing step, something along “flat normals” ?

image: dx9 is the expected behaviour, dx11 is what i get with the extruded mesh

Offhand, I would say you want to use Unweld with a value of 0 - which will visually do what Flat Shade does - then if you have internal joints at a low angle that you want to hide, you can re-weld with a small angle like 10°…