I made this “hyperdrive” slot (will have a shaft later). When I printed it, I selected 0% infill because I just want it to be a shell, no fill required. I used Makerbot, the latest version with a Rep 5 (firmware current), and selected “print supports.” It didn’t print supports that would allow it to print the top shell, other than some supports in the top of the curved part of my STL.
I made the shape by drawing the arc, extruding it, then drawing a rect, extruding it, then “intersect faces.”
Your top figure does not look like a SketchUp solid. Did you make it a Group or Component, and if so, does EntityInfo report it as solid? If not, that is likely the cause of the problem. You could try one of the Solid Inspector or SolidSolver plugins to tell you what is wrong and maybe fix it - though be aware that there are some kinds of situations in which they can’t guess your intent, hence can’t do a repair.
A Solid in SketchUp is a single Group or Component whose geometry meets certain conditions.
When those conditions are met, Entity Info indicates the model is a Solid Group or Solid Component.
Also notice Entity Info indicates the Volume of a selected Solid.
• The geometry must form a single airtight vessel.*
Like a perfect soap bubble … •No gaps •No holes •No leaks
• No extraneous Faces inside or outside the vessel.**
All Faces must serve to enclose the singular volume of the vessel.
• No stray Edges.
All Edges must serve to support a Face that in turn serves to enclose the airtight vessel.
Thus, each Edge supports two Faces … no more, no less.
• No nested Groups or Components.
*A Solid Group or Solid Component may contain one or more separate airtight vessels.
**Best that all Faces are oriented Front Side (white) facing out.