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I usually use the Shrinkwrap approach to cut any kind of hole into a curvy shape. Its work flow is to subD the base mesh to 2 levels, shrinkwrap it to the same mesh (called guide mesh) that has been subD'ed to 4 levels, then proceed to cut a hole in the base mesh. This results in a perfect smooth shape.

For this method to work, the shrinkwrap modifier must be after the SubD modifier, so I can't use this technique if I want to export the base mesh as a fbj/obj file for others to work on, because I can't apply all the modifiers. If I try to apply the shrinkwrap modifier without applying the SubD modifier first, then the result still looks not good enough because it only shrinkwraps a low poly version.

I'm getting stuck at this point, trying several methods but to no avails:

  • I tried to make sure that the faces which will be insetted are planar. This only works on a surface not extremely curvy.
  • I tried to apply the SubD/Shrinkwrap to achieve the perfectly smooth result and then use Decimate to unsubdivide it, with a naive belief that it would magically revert to the exact original topology, which it doesn't.
  • I tried to use the Knife Project tool to cut the circle into the mesh. Still same result.
  • I tried to use Data Transfer to transfer the normals information to the mesh. This works, but it brings us back to the orignal problem, because the Data Transfer solution requires geometry to work well, just like the Shrinkwrap solution.

I always get some subtle pinching like in the following image:

enter image description here

What I want to achieve:

enter image description here

So, how can I cut a circular hole into a curvy shape and have a perfectly smooth surface without using the Shrinkwrap technique?

My Blend file: cuttingHoleIntoACurvySurface.blend

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  • $\begingroup$ You spent a lot of time explaining your process but the .blend file does not have the "guide mesh" in it and does not use a shrinkwrap modifier. If you want us to check if you can salvage your process, you need to upload a more representative file. Also: I strongly recommend upgrading to 2.8. $\endgroup$
    – hatinacat2000
    Oct 19, 2019 at 13:59
  • $\begingroup$ Hi hatinacat2000, I tried to explain my work flow to clarify why I'm looking for another solution, not to ask why the Shrinkwrap modifier doesn't work in this case, so I think it's reasonable enough. But thank you for your recommendation, I'll edit my question. $\endgroup$
    – LOTR_7193
    Oct 19, 2019 at 14:07
  • $\begingroup$ Question edited with another image and an edited blend file. $\endgroup$
    – LOTR_7193
    Oct 19, 2019 at 14:15
  • $\begingroup$ There isn't anything somehow generally different if working in 2.8, improvements were made but the procedure is still the same. I don't really get why you want to avoid applying modifiers though; you can either export object with modifiers into FBX / OBJ, they will be applied and your resulting geometry will be exported; or you can export helper mesh and mesh to be shrinkwrapped. If exporting modifier stack won't be preserved anyway regardless of way used $\endgroup$
    – Mr Zak
    Oct 19, 2019 at 15:06
  • $\begingroup$ Hi Mr Zak, I can't apply the modifiers because other people will work on my mesh. If I apply the SubD, then they will find it hard to make changes to a high poly mesh. I'm apply for a hard surface modeling team, who uses 3DS Max for their work. I have no idea how 3DS Max works, but thank for your suggestion. I'll try using the Shrinkwrap technique to see whether it can be done the same in 3DS. $\endgroup$
    – LOTR_7193
    Oct 19, 2019 at 15:30

2 Answers 2

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The answer is just to have enough geometry to support the holes. The shrinkwrap modifier has spoiled Blender user for being able to make a smooth surface without thinking much about topology/geometry usually required.

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I'm not sure exactly what you need to export your file for others to work on.

One solution is to just make the hole in the base mesh, using a subD'd copy of the original mesh for shrinkwraping. This can give you a reasonably good cosmetic base mesh with a hole, or holes, which others can subD after their work.

Attached images 1 & 2 show the base mesh of a torus with a hole. The third image show it subD'd. enter image description here enter image description here enter image description here

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