Hi, roy, I send an object, with curved faces that give me problems. It's not the first time that I notice that sort of artefact, and I don't know if it comes from nXt render or autoCAD
boule.dwgmodelisation. I've trying a lot of settings on tesselation, in Acad & nXt, with Packet T. or Path T., block or not, sun orientation, I can't get rid of this phenomenon. I've modeled this seat with a sphere and booleans tools. I give the dwg and the jpg, if you have the time to check it...