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I found this answer, which I cannot comment on, so need to ask it again(sorry): Mesh disappearing when symmetrize it

I also am having the issue when trying to symmetrize, that faces disappear. At first I just thought maybe vertices were that bad out of alignment, so I refilled all the faces that deleted. However, when trying to symmetrize again(in the same spot) the faces will delete again. I then checked each vertex, and they were all exact mirror positions from 0. The origin itself was also at a perfect 0, working on an X-axis. I tried what that post answers, by setting the meshes origin to geometry. Still same effect, of faces deleting.

I also confirmed, then when using a X-mirror(editor option, not modifier), both vertices that mirror each other do move as expected, so technically they are symmetrized. Why then does symmetrize still delete faces(only on one side of X-axis)?

  • I have no shape keys
  • I do have vertex groups, which I think this area is locked(unlock did not change result)
  • I am only selecting and symmetrizing a few vertices
  • Any other questions on details, please ask before symmetrize

after symmetrize

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  • $\begingroup$ hello, maybe apply the rotation in Object mode? Oe please show some screenshos or share your file: blend-exchange.com $\endgroup$
    – moonboots
    Feb 18, 2023 at 16:47
  • $\begingroup$ All scale, rotation, and positions have been applied multiple times, as this project has been re-worked many times. And normally symmetrize does exactly what I need, it just after trying to re-do the mouth area, I am getting faces to delete when trying to symmetrize $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 16:54
  • $\begingroup$ @moonboots I do however notice the median x is somehow 0.00001. is that the reason? as somehow maybe one of the vertices is just off a hair? $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 16:59
  • $\begingroup$ The best would be to share your object or at least a part of it in order to test $\endgroup$
    – moonboots
    Feb 18, 2023 at 17:11
  • $\begingroup$ @moonboots I think I uploaded the mesh - link should be under the second screen shot $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 17:20

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I think you're not using the tool the way it should be used, you're selecting the same vertices in both sides (-x and +x) in order to replace the vertices of -x on +x, but actually it won't "replace" the +x by the -x, as you may expect, it will delete the vertices of +x and symmetrize the vertices of -x (and they will be floating as they are not automatically connected to the other vertices).

So what you need to do, if you plan to change the vertices on -x and see the result on +x, is either use the X mirror option (top left), which will move the vertices on the opposite side if the mesh is perfectly symmetrical, or make your changes on -x, select all and symmetrize.

Actually, as long as you're modeling a symmetrical object, it's easier to work with a Mirror modifier, only use the Symmetrize tool if, once the modifier has been applied, you realise that it needs some changes and it would be more tedious to re-use a Mirror modifier...

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  • $\begingroup$ I'm just trying to make sure any knife cuts I do get symmetrized, so that X-mirror works. But now that you say it, I normally do select the whole mesh and symmetrize it, not sure why I'm only selecting vertices at the moment, lol. But true, I thought symmetry just moved vertices, not replace them. I will test quick to see if it was because I was only choosing select vertices. $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 17:45
  • $\begingroup$ Got to be kidding me..... lmao, thank you so much, this problem was driving me crazy! $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 17:47
  • $\begingroup$ I always use X-mirror(after mesh was finished, and decide to make changes), the problem I found is, that sometimes when using knife cuts the mesh will become un-symmetrized. So I've gained the habit of always symmetrizing before I move onto another area, or section. But as you adequately explained, symmetrize doesn't move vertices, it replaces them. So if you don't select all, then Blender won't know to re-make faces where they are needed. again, cheers! $\endgroup$
    – WideEyeNow
    Feb 18, 2023 at 17:55
  • $\begingroup$ As I say in my edit, when you model a symmetrical object, use the Mirror modifier until you're about glad, because operations like knife or join or loopcuts won't be symmetrized with the Mirror option only $\endgroup$
    – moonboots
    Feb 18, 2023 at 18:05

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