I have been modelling a wheel-like object. I started with a torus. Stretched it out a little. Then added a mirror modifier to work on it with symmetry.

I'm trying to keep a nice clean topology. Clean topology from this side

And all was looking good until when I noticed on the mirrored side a big block of black filling in the wheel around the central hub.

I thought maybe I need to add some loop cuts to square up the faces a little more.

Now I have this weird black loop around the "rim" Weird black band on the mirrored side

These first two images are from the object with the mirror modifier.

I thought maybe it was the modifier with a bug so I duplicated the object and applied the modifier on the second version. I still have the same black banding!

If you look closely, the black band shows up from the middle of the face. It isn't the whole face that is black. And if I merge a couple of vertices, the black banding follows... sort of. The whole face isn't blackened

If I centre the view down the Y axis is highlights a familiar pattern.. Overlapping faces???

It looks similar to overlapping faces along the same plane.

But it only happens on this one side. The "mirrored" side, both before and after applying the mirror modifier.

I've checked the normals.. they are all pointing in the correct direction. Face orientation

I've checked the vertices, edges, and faces, in case I'd managed to double them up somehow.

Deleting the mirror modifier and creating it again didn't help.

It would be nice to understand what I managed to do wrong.

I expect my next step is to drop the modifier and just duplicate the side I have and weld them together to form the full object again.

NOTE: There are no materials yet defined or applied to the object as yet.

I'm using Blender 3.1.2 on Windows 11

Blender version

Here's a link to the blend file... https://www.dropbox.com/sh/tlfxrho8gf8fr77/AADZqKphYxavNtAl8izZzPCoa?dl=0


Thanks to the answer below, I now see that I apparently forgotten to check selection of vertices during z-ray mode which highlights the now obvious double up of vertices. Select during z-ray mode to see there are two vertices on top of each other


1 Answer 1


The problem is that you have two loops at the same position:

double loop

You can delete that or move it a little.

  • 1
    $\begingroup$ Ah! Thank you! I thought I'd gone into x-ray mode to help select "hidden" points but apparently I hadn't... sigh... $\endgroup$
    – BlackMael
    Apr 23, 2022 at 0:19

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