Today we look at a more precise intuitive way of using the mirror modifier. See Part 1 for a description of the “default” way to use it.
Let’s take another look at our simple object, but this time we see that the face/plane we want to use for a mirror is not orthogonal, in fact it can be any inclination in any plane:
If we try to mirror this object using the previously discussed method, this is what happens:
The best way to control a mirror operation is to mirror the object about another object. In this case we only have one object in the scene, so we need to construct a mirror object or plane. To mirror across the indicated face, the easiest approach is to construct a grid object on the plane.
Switch to Edit mode 
and select Face mode by pressing 
. Select the face we want to put the grid object onto:
Now we change our view to look directly at the selected face orthogonally. We do this with 
. Or we could use the Align View menu:
The view changes to this:
Next, we want to place the cursor onto that face. Type 
:
The cursor jumps to the middle of the face.
Now, switch back to Object mode , and type 
and insert a new Grid object:
After clicking Grid, the Add Grid panel appears. Change the Align parameter to View:
The wireframe view of the grid looks like this:
We chose a grid object instead of a plane object because it is then very easy to confirm that it is correctly placed.
Now the mirror operation is very straightforward. Select the object to be mirrored. Add a Mirror modifier to it. Click in the Mirror Object box and select Grid from the dropdown.
While still in the Modifier panel, click each Axis box in turn and choose the appropriate axis. (In this case it will be Z) :
The object is now mirrored using the Grid object as the mirror plane. This has the enormous advantage that the mirror is exact, and the original object does not have to move. The grid plane can, of course, be orthogonal, whereby you will get the same effect as the method described in Part 1 except that it will be more precise.
To finish up,
- Apply the modifier
- Delete the Grid Object
- Delete the internal face.
