Aligning faces

If there are two faces in a model that look like they’re aligned, but in actuality, they’re out by the tiniest amount, there’s a bunch of stuff you can’t do to them (like remove the line between the two faces in an effort to join them).

What is the best way to align two faces on a particular axis?

I would use the Rotate tool (default keybind Q).

  1. Double-click on the face that needs to be adjusted; this selects the face and its bounding edges.
  2. Activate the Rotate tool.
  3. Press one of the arrow keys to lock the action to a particular axis, e.g., Up Arrow constrains the rotation to be about the Blue axis. The protractor should be blue in this case. (Left Arrow locks to the Green axis, Right Arrow locks to the Red axis, Down Arrow locks to an arbitrary face that you are pointing at and shows a magenta protractor.)
  4. Click on a corner of the face about which you want the rotation to occur. This sets the axis of rotation (along with the constraint induced by the arrow key).
  5. Click on another corner of the face, or for that matter anywhere on the face. This indicates the pre-rotation starting position.
  6. Move the mouse to a target reference point, such as a point on another face or on a guide (which you might need to create ahead of time), and click a third time. This triggers the rotation, where the selected geometry is pivoted from its initial alignment to the new (third-click) reference alignment.