imported CAD mesh has normal artifacts even in flat shaded mode after merging mesh
and I cannot figure out what caused it and how to fix it.
If you select the mesh, have you this “Clear Custom Split Normals Data”?
That did really fix some of the issues but some remain.
I also played with the weighted normal modifier.
Have you tried:
- tris to quad?
- select all vertices and merge by distance to merge coplanar vertices?
- use the Auto Smooth with some angles?
CAD and 3D sometimes don’t really mix, and then it’s necessary to remodel at least part(s) of the imported mesh if all fails…
yep yep yep
I tried all of those
Unless you clean up the polygon mess at the inside corners of the legs, and some of the inside of the chair, rendering will be hard to get proper.
Like I said, sometimes the only way is to remodel parts of a imported mesh to get it right. Welcome to CAD models inside a 3d application 
I’ve downloaded and opened the file.
I don’t see the artifacts… I’ll try with some different lighting
check the model itself in edit mode, it’s rough at certain locations.
The blend file has the untouched RAW model.
It was an USDZ export and those often are fragmented because of the different texture maps the exporter produces.
Merging them together is what then creates the chaos
And I just found the solution for it:
When Merging use the “Sharp Edges” option
Great now I can reshoot my tutorial again lol …
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ah…good you solved…
Now, I’d like to know why in my Blender seems fine… 
:
Sharp Edges also works in some invalid areas.
If this is a problem, you can also try the WeightedNormal modifier. 
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WOW this is a REALLY good tip! Thanks for sharing