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I'm a new blender user, i was wondering why do i have strange black line after preview rendring my mesh, when i'm in edit mode everything looks normal, also dont't have doubles so i don't understand the problem. Can someone please help me ?? Here are some picture below to understand it better? maybe i can link the file... thanks ogject mode looks fine ( i think aha) dark edges appears when pre rendered details looks like there is no problem in the mesh

enter image description here

Gaston Janssen
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  • The topology of the hole looks like it will cause degenerate triangles on the left and right side. That might cause problems. – Robert Gützkow Aug 30 '19 at 17:12
  • So how to i correct this problem ? Change the size of the hole ? – Gaston Janssen Aug 30 '19 at 18:25
  • By fixing the topology, for instance by using knife project: https://blender.stackexchange.com/questions/5856/cutting-a-circular-hole-in-a-hollow-cylinder-without-distorting-the-cylinder – Robert Gützkow Aug 30 '19 at 18:31
  • thanks for the answer but i did every thing using knife project.. – Gaston Janssen Aug 30 '19 at 18:56
  • There is no real "easy fix" for this. Cutting holes in round shapes is one of the more challenging tasks when modelling. My suggestion would be to redo the part in the following way: BEFORE you cut the hole, add horizontal loopcuts to the cylinder so that the cylinder will consist of squares rather than rectangles. Right now, the cylinder consists of many long, vertical rectangles. Adding loopcuts will prevent resulting elongated triangles at render time. (Every mesh gets triangulated at render time) After you have cut the hole, you can manually fix any areas that still cause problems. – michaelh Aug 30 '19 at 19:29
  • Ok thanks you very much @michaelh I will try your advice ! – Gaston Janssen Aug 30 '19 at 19:39
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    Sure thing. It's probably a good idea to watch some tutorials about topology and specifically about creating holes in round surfaces. That an help you understand better what is happening here. But don't worry, this really is one of the harder things. ;) – michaelh Aug 30 '19 at 19:44
  • The LoopTools add-on can be quite useful as well. – Robert Gützkow Aug 30 '19 at 22:20

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