Problems with STL Export when using ThreeCSG


I am using Three CSG to intersect two letters created with TextGeometry. The result looks great on screen, but when I export to STL, all is not so good.

The model looks fine, but then when I come to slice it in PrusaSlicer (for 3D Printing), it’s clear there is something wrong. I can also load the file into Blender and use the 3D Printing Addon to check the model - it tells me there are 16227 Non-Manifold Edges. If I use the auto-fixing tool, the issue goes away in PrusaSlicer and I can print the object just fine.

So what I need to work out is if there is any way to me to fix this issue before exporting from ThreeJS to avoid needing to take every model into blender. I have tried all kinds of tricks on the internet but nothing has resolved the situation.

I built a minimal reproduction of my code here: where you can download the resulting STL.

Thank you so much for any help you can offer!

Any luck finding a solution to this? I ran into the same issue but pulling it into Blender to run the auto fix doesn’t work for me.