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Weird PrusaSlicer error (lemmy.sdf.org)

submitted 1 month ago* (last edited 1 month ago) by [email protected] to c/[email protected]

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So, I redrew my custom shoe model in Blender because FreeCAD just can't create geometrically-correct, smooth, complex 3D surfaces like a shoe. This one looks much better

The entire mesh in Blender is error-free. When I export it as an .OBJ file, PrusaSlicer imports it without any problems (well, it's not oriented correctly but that's easily fixed).

However, when I export it as an .STL file, PrusaSlicer imports it okay, but complains that the file contains 677,376 errors - out of 677,376 facets 🙂.

It seem to slice it without issues though so I assume the facets in the STL file are just missing something unimportant. But just in case: does anybody know what's missing in my Blender model that could cause that error?

If you want to try it for yourself, the STL file is here and the Blender file is here.

(I haven't tried to print that beast yet, mostly because the printer has been busy for work purposes all week last week and I would like to print a few test parts first. But I'm hoping to print some TPU specimens next week.)

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[–] [email protected] 8 points 1 month ago* (last edited 1 month ago) (1 children)

All of the the surface normals are backwards. This means your shoe is inside-out; instead of being a solid shoe in a vacuum it's a shoe-shaped-hole inside a solid universe.

By default blender renders all polys as double-sided so you mostly don't notice (other than some lighting oddities near corners). Turn on backface culling if you want to check if your normals are the right way around or not.

I often end up with some of my polys backwards because of the way I extrude and join parts of my models. I distinctly remember a bug in Gmax (old free version of 3DSmax) where the mirror tool would create polygons with some special, broken property where their normals would be correct in the editor, but completely wrong when exported :( much time and hassle was lost to that.

[–] [email protected] 7 points 1 month ago

All of the the surface normals are backwards

Oh wow yeah, you're right. I didn't think of checking that. I flipped them and hey-presto, just like that, it works perfectly.

I learned something today. Thanks a lot!