When exporting to STL File object doesn't form a solid when flipped

Roof Rack For printing.skp (10.2 MB)

Hi, i’m trying to export the above drawings as individual stl files to 3d print.
Everything seems to work well except the one of the 2 small mounting brackets and 2 of the side rails.
When i open them in my slicing program they appear clear instead of solid.

In both cases the objects were created by flipping the original.
test file.stl (501.5 KB)
here is the stl file i get when i export the brackets. One works fine and the flipped one doesn’t.

any help or advice is welcome.

Thanks,
Darren

These aren’t solids. There’s all sorts of internal faces that need to be removed.

Flipping objects can be problematic with some slicers. You could explode the flipped groups and remake them so they work correctly.

So far nothing I see would be considered a bug in SketchUp.

Thanks, is that an extension you’re using to view that?
I guess i never checked if they were solids after i flipped them. not sure what would cause that though.

Yes. Solid Inspector 2.

The other parts show as solids in SU. Some slicers don’t seem to be able to handle the transformation resulting from flipping a group or component.
Screenshot - 8_25_2020 , 3_41_04 PM

Mirroring components can cause flipped face normals (see the description from Thomthom), I think this behaviour is still the same in newer versions (?)

interesting that there aren’t any other issues. I found i was having the same issues with the flipped side rails as the brackets.