I use Inventor for some designs, and I occasionally face problems with exported STLs. Some of the scenarios where issues crop up (not always, but often) are:
- Assembly made of parts with different materials (Select solid / properties) - Sometimes
- Assemblies or parts where different surface materials are applied (Select surface / properties) - Almost always
- Parts which have been formed by extruding or sweeping spline faces, or have overly complex edges with fillet - Often
- Assemblies with parts not dependent on faces of grounded part, or sometimes not sufficiently constrained, e.g. spheres floating in a cage - Often
As a general workflow, I have standardized on always creating a derived part before exporting to CAD format.
- Derive style = single solid body
- "Remove geometry by visibility" checked
- "Reduced memory mode" checked
- "Remove all internal voids" checked. If one actually wants an internal void, one should be leaving a hole anyway for the ShapeWays support material to drain, barring some odd situations, so those would no longer be internal voids.
By doing this, I rarely if ever get a warning indicator when opening the STL in netfabb.
In netfabb, after the repair stage, I always use Part / Export to export the STL, even if there is no repair needed. This catches some odd issues with unmatched edges, from time to time, which you can tell netfabb to fix during export.
The resultant final STL has never failed for me on ShapeWays, no matter how messy the original assembly or part.