Shell failed: why?

Shell top flat face.
The shell at 0.5, for example, does not work. If forced 0.4 works.
(I tried to run an offset across the board, 0.5 distance, and this works.
If the offset is executed correctly, why does the shell fail? The principle of the two commands is very related …
OffsetSrf pezzo meccanico.3dm (191.5 KB)

Hi Davide - DivideAlongCreases > SplitAtTangents=Yes before shelling let’s it work here. It seems the curvature discontinuity in the single surface is not handled. Generally things will work better with tangent surfaces split up.


Thanks Pascal, a little elaborate as a passage … but Rhino is also this: many commands …

The shell fails if the emptying is performed on the upper flat face. Why? (Rhino 6)
shelling failed up face.3dm (127.1 KB)