Hi Michael,

More than likely, it's me creating sloppy cuts/curves. I tend to overlook that while prototyping objects. Which, in turn gives me problems later :)

I'm including the 3dm file. I've actually now gone back to my original form (without any windows and such) to extract an inner frame from that. I've noticed there that sometimes the shell will not yield results but the offset works.

As usual, thanks for the quick response.

Tree