Hi Michael,

Thank you for your explanations. I understand FILLETing now much better.
I was able to SHELL KleinTeil.3dm too and have submitted the shell to the 3D-Printing company.
I will receive the result in about two weeks and could show it here, if this would be of interest.

>for removing internal volumes, you can just model some rough shapes and put them inside the model and use boolean difference to make them cavities within the main shape -

I will follow this very helpful suggestion, which meets my objective of reducing 3D-Printing costs :-)))

thanks & regards
Jurgen