Hi Michael,

& thanks again for your feedback & help!

I found the tiny edge you indicate on your picture in the model and when I selected this edge as well I was able to make the surface without any further issues. :-)

So, after checking things again I sent it off to printing today. So now I look forward to actually molding my objects inside the model ...

Thanks again & the best for your weekend (when it comes to you in your part of the world).

Jesper