I'm a Blender newbie and I'm trying to use it to make a simple model for a 3D project. I'm trying to edit a cube with a mirror modifier to make a symmetrical shape, but when I drag some vertices to a side in edit mode it creates new vertices on the other side instead of moving the symmetrical equivalent:


What am I doing wrong?

  • $\begingroup$ All of the vertices of your "cube" need to be to the right of it's "origin" (The orange dot). You will also want to check the box next to "Clipping" in the Mirror Modifier panel. $\endgroup$
    – Dontwalk
    Commented Feb 23, 2018 at 18:41
  • $\begingroup$ What do you mean with "right of it's origin"? Also, if I activate the clipping nothing changes. $\endgroup$ Commented Feb 23, 2018 at 18:44
  • 1
    $\begingroup$ The "Mirror Modifier " mirrors around the objects Origin. vimeo.com/46062005 $\endgroup$
    – Dontwalk
    Commented Feb 23, 2018 at 18:47
  • $\begingroup$ I see, so it only adds vertices and in the end I'll have to delete the initial cube? $\endgroup$ Commented Feb 23, 2018 at 18:54
  • 2
    $\begingroup$ Watch the tutorial that I linked... The "Mirror Modifier" mirrors exactly what you have on one side of the objects "Origin" to the other side. In a simple scenario you shouldn't have to delete anything. You may want to "Apply" the modifier (in Object Mode) but you don't necessarily have to. $\endgroup$
    – Dontwalk
    Commented Feb 23, 2018 at 18:58

1 Answer 1


The Mirror Modifier, unless it's configured differently, mirrors a mesh around the Object Origin. It duplicates any geometry on the other side.

Usually you shouldn't cross the mirror glass. But when you add the default cube, 4 verts are left of the O.O. and the other 4 are right of the O.O. So it's not the best place to start.

Here are the 4 stages, shown with cubes:

  1. Every vertex is on the left side of the middle, everythings fine.
  2. 4 verts are left and 4 verts are in the middle. That's where clipping comes in. It will glue any verts to the middle that try to cross it. It doesn't repair any tresspassing. Be careful when you do that with a cube. It will trap a face in the middle which can lead to unclean topology.
  3. That one's not too healthy: most cubes are on the left side but one is on the right side. You can do that but it requires more attention.
  4. That one causes sort of bad geometry. the original and the mirrored mesh intersect, edges are crossing the line. z-fighting can occur when the faces are parallel to the mirror axis.

Now, technically you can do any of that, you just have to be careful not to cause unwanted effects.

enter image description here


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