I am trying to create a ring for 3D printing. Part of the requirements for 3D printing is to not have any non-manifold geometry in your model. When checking whether I met this requirement, I found that my model contains two edge loops consisting of "Boundaries" non-manifold geometry.

Highlighted in orange are the non-manifold edges of type "boundaries" (Highlighted using Ctrl + Alt + Shift + M, only Boundaries is toggled so that I could narrow down what type of non-manifold this is): Non-manifold edges (boundaries)

When I zoom in and move some of these edges aside, I find that there exists a duplicate edge loop underneath!: Here, you see that there is a duplicate loop hiding underneath my loop

I undo that translation, reselect the non-manifold edge loops through Ctrl + Alt + Shift + M, and I "Remove Doubles". Here, I find that the hidden duplicate loop no longer exists, but now my non-manifold edges are of type "Non Contiguous": Non-contiguous edge loops

I read that non-contiguous edges are due to face normals being in opposite directions(?). Turning on face normals, I get this: Face-normals

Honestly, I am new to 3D Modelling and Blender, and am not sure how to correct my issue from here. Do you guys have any advice?

Edit: Here is the .blend file prior to the modifications mentioned in this post:


1 Answer 1


In this case:

  • Select all vertices, and (M) Header > Mesh > Merge > By Distance
  • Then, with all still selected, (AltN) Header > Mesh > Normals > Recalculate Outside.
  • $\begingroup$ At first I tried this with just the non-manifold geometries and it didn't work, but explicitly following your instructions and doing this to all of the vertices did the trick. Thanks!! $\endgroup$
    – Logan
    Oct 6, 2018 at 17:52
  • $\begingroup$ Sadly, this no longer works. In 3.5, it broke me mesh (thankfully undo works better these days!). :) $\endgroup$ Apr 29, 2023 at 2:26
  • $\begingroup$ Hi @SeanRobertson.. sorry you had a break! I just retried this, (with updated shortcuts: M for merge, and Alt-N for normals) on the original heart mesh.. and it worked for me. It''s not exactly a very general Q or A, though.. more one of those 'fix this particular case' questions. Not sure it's very useful to the archive. Maybe it has to go. $\endgroup$
    – Robin Betts
    Apr 29, 2023 at 6:12
  • 2
    $\begingroup$ Hi, @Jay! Point taken, but. A bit of a quandary, this one.. not only have the key-mappings changed, so have the menu items, so even if I hadn't used keyboard shortcuts, the answer would still have been misleading, for more recent versions. Personally I can't see a way of getting round this, except expecting the reader to take into account the date of the posts, and relying on folks to come in with an edit, where they spot it's appropriate. Thanks for the heads-up, I've edited, ( until the next time :) ) $\endgroup$
    – Robin Betts
    Dec 24, 2023 at 9:00
  • 1
    $\begingroup$ @RobinBetts There's enough version churn on Blender. Perhaps the blender foundation has addressed the issue. Thanks for helping $\endgroup$
    – Jay
    Dec 24, 2023 at 15:42

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