Hi Joe,

  We currently repair STL atomic structure models using Microsoft's online Tools3D site as described in Tom Ferrin’s message below.  Since it is online that step could be done from a Mac (use Firefox, Safari does not allow upload for some reason).  You need a Microsoft account and it asks you to give permission to share all your email contacts, or some such non-sense and does not let you proceed unless you say yes.  I don’t understand that because it does not have access to those contacts since I don’t install anything on my machine, so I judged it harmless although annoying.  The Microsoft repair supposedly uses Autodesk and netfabb in the cloud.  We used an academic free version of Autodesk (on Windows only) to get similar results with more effort.  The Microsoft tool does not return STL, instead giving a .3mf file which needs to be converted to STL.  That can be done (on Window) with the Microsoft 3D Builder app.  At any rate, this whole process works ok on Windows and produces a good quality mesh removing intersections of ribbons, atom spheres, and bond cylinders to produce a single closed mesh that the 3D printer software can handle.

Tom