Step 3: Notch out the vertical post
The easiest way to notch out the vertical supports is to drill out the corners with a 1/4" drill bit. And then use a coping saw or a jig saw to cut out the rest. The notch on the 2" x 4" is 2.5" in from each side and 4" down. This will make the notch a little bit big, so you will have to cut within the lines.