Cut a piece of 2x8 lumber to the desired length (about 9') to form the seat board. Cut a piece of 2x4 to the same length to form the brace board.
Cut two sections of 2x8 lumber to 35" for the uprights of the seesaw. Sand the edges smooth.
Dig holes for the uprights, using a posthole digger if desired. Secure the uprights in the ground at least 17 inches deep, leaving 18 inches above the ground. The uprights should be set about 7-3/4" apart to accept a 2x8 seat board between them. Set them securely in the ground with quick-drying concrete.
Using a jigsaw, cut out a U-shaped notch 2-1/4" deep in the top of each upright. The notches will accept the pivot bar made of 1-inch galvanized pipe.
Cut a U-shaped notch 1-1/4" deep and 1-1/4" wide in the center of the brace board.
Mark a line lengthwise down the center of the seat board and, using Liquid Nails construction adhesive, attach the brace board with the notched side down. Reinforce with galvanized screws, driven from the top of the seat board every 6 inches along its length.
Position a piece of galvanized pipe in the notched area. The pipe should be long enough to allow a 1-1/2" overhang on each side. Add pipe straps to further secure the pivot bar (Image 1).
Drill 1/4" holes in both uprights to allow placement of locking pins -- metal dowels that will keep the pivot bar in place (Image 2).
To make the handles, measure in 16 inches from the end of the seat board and 1-1/4" from the sides. Drill two 5/8"-diameter holes to accept marine-rope handles. Insert the rope, and tie knots in the ends to secure it. Singe the ends of the rope to keep them from fraying.