Thanks, Matt. Those circles were made that way, one circle and a 1MM offset. I don't know how they got polygonish. Polygeist?

Thanks for the Hidden Geometry tip.

How did you see that the edges had bits that were askew? I tried to look across the edges and they looked good. Is there some precision trick to compare planes?

Take a look at the attached screenshot clip.  I've selected the button on the toolbar that says "A1" and then picked various endpoints.  The label defaults to having the point coordinates (there's probably a way to change the displayed accuracy but I don't know offhand what that is.

I moved the model around a little, but you can see where these points all lie 1mm above the "0" horizontal plane.  Except one, which is at ~1.0mm.

The obvious question is "is there a way to edit the point to move it to the desired Z coordinate while leaving X and Y the same" and the short answer is I never looked around to try to figure that out.

Hope that helps a bit ...

Thanks for the Hidden Geometry tip.

How did you see that the edges had bits that were askew? I tried to look across the edges and they looked good. Is there some precision trick to compare planes?

As always, thanks for your time, pal.

Regarding the model you've been working on : there are a number of points that are on edges that don't form a plane where you would expect it.  In other words, two edges of what should be a flat surface have points on them that are slightly off the plane.  So SU puts in some hidden geometry that is seen as a "shard."  If you go to "View" and check "Hidden Geometry" and also explode the model as much as possible and "Show guides" you'll see a lot of items that could probably be cleaned up.

Sorry I can't produce a clean a version for you, but it's evolved to a point where I think only you know what should be where.  I would suggest replacing the two interior polygon "circles" with extruded circles (one that's 13mm in diameter overlaid on one that's 14mm diameter; delete the internal circle and extrude the remaining ring.)

Not that I have an answer for you either way. I'm still using the last version from before they switched to the new branding. Although, even when SketchUp was still at Google the updates seemed few and far between and bugs had a long shelf life. Trimble doesn't seem to be doing any better, at least in my experience. About the only reason I still use it is because the price is right.

Do you think they are concerned and working on these thing (crashes, tendency to go non-planar, reversed face 'shards', etc.)?

I've considered switching to Wings or Bender or something but the other stuff either looks like it was built for Pixar or underfeatured. I couldn't get Wings to import my STL even though NetFabb and Repetier will. Even after NetFabb had repaired and blessed it, Wings refused to take it.

What's a mother to do?