Flipping and mirroring can be used when you want to repeat an element in the opposite position, but these tools are also very useful when you want to model symmetrical objects. Modeling half of an object has several advantages. It reduces the geometric entities; it takes half the time to complete items such as chairs, beds, sofas and tables; and the changes applied on components will be reflected in the mirrored copy.
I am using a presidential chair to illustrate this concept. To model half-chair I used a Photo Match function that allowed me to complete it in a few minutes. Mirroring allows you to duplicate that half to create the rest of the model.
There are two features that can be used for this procedure.
The first is to use the Scale tool by pulling a grip toward and then beyond the point about which you are scaling. This operation allows you to pull geometry inside out. Note that the grips snap to certain negative values (such as -1, -1.5, and -2) just as they do in the positive direction. You can force a mirror by typing in a negative value or dimension.
1. Select the object and make a copy.
2. Choose the Scale tool.
3. Pull geometry inside out. Note that the grips snap to certain negative values. Type -1.
4. Move the second half into position and use Shift+Erase to hide the edges.
The second way to achieve the same result is by using the Flip Along operation.
1. Duplicate the object.
2. Context-click on the geometry.
3. Select the Flip Along context menu item.
4. Choose the axis for the flip. Tip: if you are moving the object along the red axis, the green axis will be the mirror line. In that case flip along green; same using the other axes.
5. Move the second half into position and use Shift+Erase to hide the edges.