Bridge edge loops difference between 2 circles and the same circles extruded

Question

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)

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)

Now if I extrude the circles (I removed the faces previously created)

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

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!

Answer 1

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

Answer 2

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

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.

with this result:

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.