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I am very very new to blender and have seen similar questions but just need an explanation - I have finally succeeded in cutting the edge off a cube using the boolean modifier here -

enter image description here

and I need to know how to make this EXACT same cut on the other side. I have gone over many tutorials and attempted to use the mirror modifier but the best I can come up with is duplicating the object, flipping it and trying to join it to the original. There must be a better way here.

How can I mirror any modifications I make to an object across 1 axis of the object?

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  • $\begingroup$ Just wanted to add that for this particular mesh manipulation you can simply select the edge and press Crtl+B for Bevel, if you don't need the exact measures of the cutting object. Selecting the edge on the other half will result in what you want to achieve here. $\endgroup$ – Dimali Apr 7 '17 at 23:18
  • $\begingroup$ I can't see any reason to not use Mirror modifier in this case, either before creating that beveled edge on the top or after. $\endgroup$ – Mr Zak Jun 18 '17 at 22:54
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Blender wont mirror operations made on a mesh but will mirror the mesh itself, in the state it is when the mirror is applied.

So, most of time, you may anticipate that your shape will be symetrical and define the mirror appropriatly.

By default, mirror is applied along the x-axis (1) and at the center point of your mesh (the yellow dot you can see in object mode marked 2 here). In this example the mirror position corresponds to the plane defined by X=3, as the mirror is on X and is defined relatively to the object's center at the position (3, -1, 0).

enter image description here

This previous image shows a cube. But in fact, only a half cube is defined in this example :

enter image description here

This half cube is not a plain figure, but some kind of open box as a face is missing (see above) because the final mirrored cube does not need an inner face (at least this is the most common situation but this is not mandatory).

Once the mirror is placed and if you want to use the boolean modifier, some tricky things may happen (boolean modifier is not allways so simple) : or the intersecting object is not itself mirrored or it is :

enter image description here

If it is not, all is fine, and you obtain this kind of result when you apply the boolean modifier :

enter image description here

But if it is the two shape will be intricated, and that's probably not what you want :

enter image description here

So to avoid that, an easier way is to work on a half of the model (not mirrored) and add the mirror modifier once finished with the boolean.

In my opinion (but the following remark may be considered as subjective), using the boolean modifier is not the simpliest way to start using Blender, even if it seems "simple" at first sight (it may also have some other unwanted consequences). So for a begining, I'd suggest to keep using the mirror modifier (if you need it) but go in edit mode to model your shape manually.

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  • $\begingroup$ I've tried to follow your answer but I'm only able to mirror after selecting another object (i.e. camera or lamp) and this results in the mirrored object stuck on a different axis.. what am I doing wrong here? $\endgroup$ – skyguy Jun 20 '16 at 4:10
  • $\begingroup$ @skyguy can you provide a screen capture of this ? $\endgroup$ – lemon Jun 20 '16 at 6:09
  • $\begingroup$ Good detail to your answer, but the premise to it is simply not true. See my answer for further clarification. $\endgroup$ – JakeD Nov 16 '16 at 18:27
  • $\begingroup$ @pycoder, this question was bumped just now... and after a new read, I still wondering... what is false 'in the premise'? $\endgroup$ – lemon Mar 8 '17 at 14:58
  • $\begingroup$ @lemon If you do what I showed in my answer, the operations can be "mirrored". You said that "Blender wont mirror operations made on a mesh," but this is not true. $\endgroup$ – JakeD Mar 8 '17 at 22:28
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Blender does allow you to do this, but a mirror modifier is more often used:

enter image description here

Just enable the X Mirror option in 3D View > Tools > Options > Mesh Options > X Mirror. Note that this will only mirror along the x-axis (that should be your mirror axis anyway) and will only work if the mesh component (vertex, etc.) is at the exact same position as the one on the opposite side. To insure symmetry use the Mesh > Symmetrize tool.

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