I always have trouble rendering curved surfaces. This isn’t just in this model—it happens pretty much every time there are curved objects in my models. Suddenly, there are very sharp light/shadow edges on the surfaces. It doesn’t matter whether I have the sunlight turned on, and it doesn’t matter which light type I use. Does anyone have any idea what might be causing this? I’d really appreciate it if someone could comment on this—thanks! 
Systeminfo.txt (2.3 KB)
In your first images that looks like discontinuities in the normals on the surfaces.
For most of the images to my eye that looks like a specular reflection on the highest point of the curved surface to the viewport. I’m going to guess you have a high window behind the viewpoint and you have e completely empty outside scene, fully white.
Perhaps turning the reflectivity of your wood material down would help, or not have fully white only environment outside your windows.
Unfortunately, none of that works. I can completely remove reflections or make the background black, but it doesn’t change anything… I don’t think there’s anything obvious in the settings; I suspect it’s some kind of rendering error, unfortunately.
Do you have a texture on it? looks a bit like the texture is not seamless at all? One side is darker than the other
Yeah, but unfortunately, that has nothing to do with it. This happens with textures (even when they’re mirrored) and also with simple materials like plastic or plaster—it doesn’t matter…that’s why I uploaded several versions of the images to show this 
what are your rendermesh-settings ?
do a minimal sample - a cylinder or similar where this effect happens. skip using extrusions (convertExtrusions) In Properties set a custom, very fine render mesh.
still there ?
_extractRenderMesh to see if this somehow corresponds with the artefact.
make sure to check if some bump-map is set.
remove it to see if this is the devil.
my 2 cents.
good luck in trouble shooting.
tom
Unfortunately, none of that solves the problem either. It happens with solids, surface groups, Subds, etc. The material doesn’t matter. With or without a bump map, with or without a texture…
Thanks for the ideas. Maybe someone from the Rhino team has another idea about what might be going wrong in the program. As I said, I don’t think it’s a problem with the settings. Thanks a lot
