Mirror Modifier not working in Blender

Mirror Modifier Not Working in Blender? – Part 1

Actually, it works very well, but mirroring something is not quite as apparent as we might expect. Why the Blender programmers don’t make it as easy to use as CAD programmers do is a mystery to me. But… what do I know? I’m not a programmer.

Consider this simple object. It’s just a cube with two edges bevelled so we can easily see what is happening. The object origin is located at the world origin; the cursor is located at the object origin. So it can hardly get more straightforward than that :

A simple object with its sides clearly identifiable

Now let’s mirror it so that the filleted edges are mirrored to the other side. Select the object and add a mirror modifier.

Nothing happens!

Ok, let’s push some buttons on that modifier…

The only time anything seems to happen is if we press the Y axis button

And then the object seems to turn into a cube!

What’ going on?

Well, let’s see if turning on transparent mode and Wireframe mode helps clarify matters…

Wireframe Mode with Transparent mode toggled on
Ah! Now we see what is going on.

The object is indeed being mirrored across the Y-axis. Still, because the Y-axis (The red line in the image) runs right through the middle of the object – it is actually mirroring about itself.

So how do we Fix this Mirror?

This is the point where Blender becomes non-intuitive but is quite logical if you think about it.

Switch to edit mode Tab Key and select the image:

The original shape is selected – it’s mirror structure is not highlighted because the mirror modifier has not yet been applied.

So now we move the selected edges away from the red X axis in the Y Direction (The green axis).

We wind up with two shapes

If we want them to join one another “back to back”, we simply move G Keythem back in the Y direction until they meet:

Original and it’s mirror back-to back.

Tip

If you check the Clipping box in the Mirror modifier panel after you have brought them together, this acts as a sort of glue.

Click the Clipping checkbox to apply “glue”

Now if you move the selection outward again, it stays glued together and simply extrudes the joining faces:

Glued together

To finish off, toggle to object mode Tab Key and apply the modifier:

Apply the modifier by clicking the down arrow and then click Apply

This is the simplest way to mirror an object, but there are some problems with this method that may or may not affect you.

  • The first problem is that you are physically moving the object you already made. This may or may not be a problem to move the original object back to where it was.
  • If you are trying to model precisely, the two flat faces may not perfectly coincide without some fiddling.
  • There will be an internal face created after applying the modifier.
  • If you want to mirror across a plane that is not parallel to an axis, the mirror gets very difficult to construct.

Click Part-2 to look at a more intuitive precise way of mirroring…

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