STL export from Rhino has bad faces, need help

Hi all,
I’ve created an object in Rhino that I’m trying to 3d print.
The model is solid and clean as a nurbs object inside Rhino. And I get no ‘naked edge’ warnings when I export the model as an stl. -The exporter is happy with the model.

However when I open up the stl back into Rhino and other 3d apps - there’s a handful of these errant polygon faces.

I’m not sure what to do about them?

There’s not too many of them, it wouldn’t be hard to simply select and delete them all. But I’m weary of invalidating the stl by doing that?

Has anyone seen this kind of thing, and know what I might be able to do about it.

The inner rim has a whole lot of out-dented writing on it. Initially this was giving me a lot of problems generating a water tight, solid, stl with no naked edges. Eventually I solved that issue by booleaning the text one by one, instead of all together. However stumped on this issue.


Hi Simt - most likely the text has a loop in a trim curve - text is often pretty hard to work with as the curves tend not to be very good to begin with, and then flowing onto a surface adds a stage of potential degradation. It looks like the skinny ring with the text is not shading properly as well- that is another indication that the trims need a look. Can you post the file or send it to


Hi Pascal,
thanks for the response. I’ve emailed an attachment of the file to


Hi Simt- Can you please also post/send us the flat text? I assume this was 'FlowAlongSrf-ed", correct? There are many minute zigzags in the letter surfaces and this makes the trims there loopy. I think we can find a better way to get this text flowed if we can have the original flat version.


Hi, a big thank you to the McNeel people.

Via email I got a response from Brian J, in it he said,
“Right now the trim borders of the flowed text objects appear to zig zag
back on themselves creating bad edges in the trim surface. I would try
CurveBoolean on the flat curves prior to flowing especially if they
originated in Illustrator where this is known to happen.”

The text curves were indeed from Illustrator and after I ran them all through a CurveBoolean - it all worked. I got a nice clean surface that exported out nice and cleanly.

Again a big thank you.


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