I’m using the Shell command more and more. It’s rather handy for both architectural and 3D-printing applications. It’s a neat feature, however even after the latest update, which promised more reliability, it’s still rather flimsy even with simply geometries.
just for others that need a simple _shell - workarround and dig in the forum:
(1 - simple)
sub-select (Mac: cmd-shift-klick, Pc: ctrl-shift-klick) the surface for the opening
_offsetSrf (solid=yes)
(the flange is perpendicular on the faces surrounding the opening)
(2 - maybe nicer flange)
_extractSrf (copy=yes) (the face to open)
_offsetSrf (solid = yes , above face, Distance as much as possible)
_offsetSrf (the input geometry, solid = no, the shell-thickness, flip normals inward)
_createSolid ( initial closed Surface + both offsetSrf’s results)
delete unneeded geometry
if createSolid fails - try trim join.
if further problems try with corner setting of _offsetSrf round or sharp
the flange is perpendicular to the removed face / opening