3D model issues after STL Import with smooth shading

Hi everyone.

i’m new to these forums, so I hope I put my question to the right category.

I’m currently working on some rendering which should in the end be as photorealistic as possible. I got the 3D models provided and they were exported in a quite high poly version from Solidworks in STL format.
First of all I have to admit that this is the first time for me to work with stls… however, basically almost everything works as it should… almost. My problem occurs when I render the models with the shading set to smooth. It messes with some of the reflections, but only some of them. See picture attached.
So, a Subsurface Mod doesn’t help, Auto smoothing doesn’t help (read somewhere that this is because of the STL), Subdividing doesn’t help… i’m running out of ideas :-/

Has anyone here experiences with problems like these? Whats the problem with these models? Is it a problem between Solidworks and Blender? What’s the quickest or easiest way to solve them.

Any help would be highly appreciated.

additional Info:
i’m working with Blender 2.79 (daily build), cycles render, principled shader, 3k textures from poliigon, the image attached was rendered in 4K at 200% and is zoomed in to … however I don’t really think this info helps much, as I think the problem is caused somewhere else.


It doesn’t, that’s why one prepares and uploads an example .blend file of the problem. A small piece of geometry in a file to replicate the issue with should also carry the cause of the problem

Auto smooth cuts the shading on the edges above the set angle, and edges marked as sharp. Stored normals can override that, which could come from import but not sure .stl has that. Those are cleared in object data properties -> geometry data.

There’s no subsurface modifier. It’s subdivision surface modifier. It affects the surface, not something below it.

STL format is the absolute worst quality for rendering. I’ve seen people use ZBrush to retopologize STL meshes, but then there’s the ZBrush license cost.

The best solution is to use Moi3D with an STP export from SolidWorks. Moi3d saves quads in Obj format, with smoothing normals. And its less than half the cost of a ZBrush license.

It’s not the file format’s fault that a CAD package exports crappy meshes. Getting it in quads with custom normals might help to hide it for rendering, but it’s still crap.

There’s no example file so can’t check the geometry. The fix in this case might be simple. An external program could help speeding up retopology but that can also be done in Blender.

Yes, the mesher is the problem with the cad application, so its not specifically STL. Since 3D printers don’t really care about the aspect ratio of the triangles, most meshers in CAD apps don’t either. The end result is typically poor for rendering across the range of cad apps.

… Which is why Moi3D is unique. The mesher in Rhino is improving, but its not as good as Moi3D.

STL does not retain smoothing normals, so in that respect is is partially a format issue.

I’ll upload a .blend file later today so you guys can get a clear picture of what’s happening. I really appreciate your help and thanks for being patient with me :slight_smile:

In case you want to clean up that STL and export in a better format for importing to blender.

Thanks for your help so far and sorry for not uploading a blend file earlier… Problem is that my colleagues exported the object in a very high-triangle setting, so even when I reduce it to only a snippet of the surface, the .blend file still has 110Mb and obviously exceeds the upload Limit here. The the body of the spray gun, as shown earlier has almost 3.500.000 edges and 2.300.000 faces.
Sorry, but I can only provide it on dropbox https://www.dropbox.com/s/ams4qzwt74jhn9l/export2.blend?dl=0

I did some trying out in blender and I found out that enabling smooth shading with an Auto-shade set on 2 degree currently is the best compromise handling the mesh… although I have to admit that the rendered result is a compromise as well.
I’d really appreciate your help with this.

Currently I’m trying out all the different options you gave me. Also, from tomorrow I can check other export options from SolidWorks so if you have any reccomendations on how to proceed your help will be highly appreciated.

Thanks in advance!