Cut a notch in the top of the two tall boards large enough to hold the smaller board snugly. The small board is the crossbeam and the two longer boards are the side posts. Place the crossbeam in the notches, in the side posts, and lay the formation flat. Line everything up so that the side posts are parallel to each other, and 22 inches apart.
Drill two holes through one of the side posts and the crossbeam. Repeat this process for the other side.
Position the crossbeam inside the two notches and secure it with glue. Thread wood screws into the drilled holes. The crossbeam should now be securely attached to the side posts. This completes the frame for the wooden swing.
Pick a level area to build the swing. Dig two holes 3 1/2 feet apart and 2 feet deep. Place a thin layer of gravel at the bottom of the hole for drainage.
Have an assistant help you lift the two side posts of the frame and slip them into the holes. Make sure the crossbeam is level, then pour quick-drying concrete around the posts. Add water per manufacturer's instructions to the concrete. Allow the concrete to dry before installing the swing.
Sand all of the rough edges of the 2-foot-long board. Pay particular attention to the corners, as this will be the swing.
Thread a screw-in shackle onto each end of the swing board. Screw the remaining two shackles into the crossbeam of the frame, 2 feet apart from each other.
Place an "S" hook through each of the shackles in the crossbeam. Hook a length of chain on each "S" hook.