Converting STL to STP self-intersecting faces error

I’m fairly new to SketchUp, and learned/used the web version today to create this 2 piece part. I wanted to convert the STL to a STP file for machining and am using FreeCAD 0.18. When I go to analyze the mesh, the only option that prompts repair is for self-intersections (repairing this caused the mesh to be unusable). Not really sure where I went wrong in SketchUp to cause this, but if anyone could take a look and get back to me that would be great, thanks.

Panel Comb.stl (115.4 KB)

Try these, I cleaned them a bit and aligned them to an axis.
I can’t see any specific error that would relate to that error message.
Comb Box.stl (706.9 KB)

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Hm it still is having issues when I evaluate and repair the mesh. I’ve attached a screenshot of what it looks like when I repair the self-intersections, it looks like it’s deleting parts of faces which makes it not a shell and thus unable to convert to solid.

Solid Inspector 2 throws an error when inspecting the left hand STL object imported into a new .skp file, and shows surface border errors in the right hand one where the red lines are:

Can you upload the .skp file instead of the .stl one?

You may be running into the ‘small faces and edges’ error in SU. It cannot create, and may merge, very short edges in SU.

Search the Forum for the Dave Method to see one way to fix this when modelling the original in SU - essentially, work on a scaled up COPY of the original COMPONENT, at 1000x scale size. The original scale component will inherit the scaled down edges and faces, without collapsing them if they are very short.

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Looks like scaling it up then editing has helped. Also noticed that when I separate the parts into 2 files and then load each to FreeCAD it recognizes the shape I make from mesh as a shell and converts to a solid. Thanks for the help here, hopefully will be good from here! Will definitely post back though if I have further issues.