can't find inverted normals

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First look :

You have some double faces, for example :



On the left shows which part, on the right what's inside:
the striped poly's are double, two faces with different normals in the same place.

They are caused by different shells of which faces are on the exact same spot but oriented different.

You are also using a lot of multiple shells (my software counts 82 shells, this can cause all sort of problems.

Try making everything into one manifold shell, using boolean functions.

Model was done on commission for me because I'm not much of a 3d modeler. So while I have a vague understanding of what you said, I really don't know how to fix it. They were supposed to be done for rapid-prototyping. My normal print bureau would automatically fix them, but they need to be perfect for Shapeways. Thanks for the insight and I'll see if I can learn anything from it.

VirtualV was kind and took care of this. He did a fantastic job on it. Thanks a ton.