The STL files have 'merged' components, as opposed to 'union-ed'. Since STL is just a 'bunch of separate triangles', all geometrical clues about this situation are lost, and this causes them to be unable to be used with the CGAL library in OpenSCAD (used for exporting). There's no workaround or possible fix for this.
For example, If I slice this stl in half through the center line, I see this 'box' intersecting, but not interacting with, the rest of the case.
Through the 'hole' that's not supposed to be there, you see rogue faces (because the preview doesn't know how to handle two front faces or two back faces in direct succession)
Long thread about STL difficulties (not exactly this issue, but something related): http://forum.openscad.org/Model-Not-rendering-CGal-error-td22122.html
Also, some slicers will do wrong things, as explained here: https://www.afaik.at/post/mergeopenscad/
The STL files have 'merged' components, as opposed to 'union-ed'. Since STL is just a 'bunch of separate triangles', all geometrical clues about this situation are lost, and this causes them to be unable to be used with the CGAL library in OpenSCAD (used for exporting). There's no workaround or possible fix for this.
For example, If I slice this stl in half through the center line, I see this 'box' intersecting, but not interacting with, the rest of the case.
Through the 'hole' that's not supposed to be there, you see rogue faces (because the preview doesn't know how to handle two front faces or two back faces in direct succession)
Long thread about STL difficulties (not exactly this issue, but something related): http://forum.openscad.org/Model-Not-rendering-CGal-error-td22122.html
Also, some slicers will do wrong things, as explained here: https://www.afaik.at/post/mergeopenscad/