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I'm still fairly new to blender and can't manage to understand what's happening here. I have 2 circles: one has 12 vertices, the other 60 (multiple of 12) enter image description here

if I loop select both circles and use the 'bridge edge loops' function it works perfectly (well almost, you can see the number of vertices connection is uneven) enter image description here

Now if I extrude the circles (I removed the faces previously created) enter image description here

and do the same with the top circles the result is completely different (and not what I expected) - same happens if I try the bottom circles enter image description here

I did try to recalculate the normals even if I read the bridge edge loop doesn't account the normals and it didn't have an impact indeed.

anyone could explain why is it happening? and if there's a better way to get there: My only solution so far is to create the top face, the bottom face, and the extrusion as 3 different objects then join, merge vertices (by distance) and recalculate normals. it works but seems like a tedious overkill.

Thanks!

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    $\begingroup$ if you flip normal of inner tube it should work... $\endgroup$
    – alambre
    Mar 6, 2022 at 18:52

2 Answers 2

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I think you can use face normals to tell the operator what you expect it to do...

face normals

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  • $\begingroup$ thanks a lot for the explanation! I could make it work $\endgroup$
    – Malisz
    Mar 7, 2022 at 2:32
  • $\begingroup$ interestingly if I extrude following Z going down normals are not flipped, only if I extrude going up... I wonder why and if extruding down shouldn't be the best practice $\endgroup$
    – Malisz
    Mar 7, 2022 at 3:17
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This answer is correct in stating that because the extrusion caused the inner cylinder's vertex normals to be flipped, pointing inward, the basic bridge tool gets confused as to which inner vertex to match to each outer vertex.

You can, as the answer suggests, manipulate the vertex normals so that the inner cylinder's point out and the outer's point in.

But an easier approach that allows more control is to enable the Loop Tools add-on

Loop Tools addon

Once you have it enabled, you should be able to produce better results in situations such as this. You can access the Loop Tools from the context popup menu (shortcut Right Click) and use Loop Tools → Bridge to accomplish the bridge.

context menu showing loop tools submenu

with this result:

properly looped edges

Loop tools tends to do a good job of understanding what should be inside or outside of the resulting bridge without referencing the vertex or face normals, and works even if you are using custom normals.

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  • $\begingroup$ thank you. I tried it and it works perfectly, much easier than checking/flipping normals $\endgroup$
    – Malisz
    Mar 7, 2022 at 2:32
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    $\begingroup$ You're welcome. Loop Tools is one of those add-ons that's rarely mentioned but incredibly useful. $\endgroup$ Mar 7, 2022 at 16:16

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