Drill a hole, using a 13 mm drill bit, 5 3/8 inches from one edge in the center of each of the 20 inch wood pieces. On the other end of the planks, drill a hole 2 3/8 inches from the edge and another hole three inches from that hole. Drill holes in the 13 1/2 inch piece of wood in the center of each side, 1 1/4 inch from the edge.
Lay two of your 20 inch pieces on the ground and align the single hole in them that is 5 3/8 inches from the bottom of the piece of wood with the holes in the 13 1/2 inch piece so that it resembles the letter "H" in shape. Place the two remaining 20 inch pieces of wood on top of the 13 1/2 inch piece and align the same holes. Insert the carriage bolts into the holes you just aligned to hold the pieces of wood together. Tighten nuts onto the end of the carriage bolts to hold the bolts secure.
Place thin boards, metal or any material that would be strong enough to hold concrete into the inside of the tire.
Make a mix of concrete using six spades full of gravel, four spades full of sand and two spades full of cement. The ratio should be one part cement, two parts sand and three parts gravel. Mix the ingredients together before adding water. Fill the wheelbarrow three-quarters of the way full. Add a half standard bucket of water to the mix. Add a little water at a time while using the spade to fold the concrete over. Keep mixing the concrete until the consistency is even.
Use a shovel to put concrete into the tire. Add a little concrete at a time and allow it to enter the rim of the tire. Be careful not to add too much concrete or it can be hard to install the support into the tire base.
Place the wooden piece you just built down into the tire so that the two sets of drilled holes are at the top and the first single set of holes that have galvanized screws in them are above the tire rim. Shift the wooden piece until the bottom settles at the bottom of the tire. Make sure that the first set of holes is above the tire rim before adding concrete. Fill the remainder of the tire with concrete. Use a tool to poke around in the tire to ensure that all of the areas in the tire have been filled.
Place a straight wooden plank up against the side of the wooden support unit on the tire. Place a set square on the plank to check that the wooden support unit is at a right angle. Check each side to make sure that it is at a right angle.
Use a set square as a guide to mark a center dotted line on the middle teeter totter plank. Mark two separate solid lines a half inch on either side of the center line. This will be the space where your pivot bar will sit.
Use three nails and slightly hammer them into the lines you marked. Hammer one nail toward the top of one solid line, another nail on the opposite solid line in the middle and the last nail hammered on the bottom of the line where you hammered the first nail. The nails will hold the pivot bar in place.
Place the pivot bar in between the nails and make sure that equal sides of the pivot bar are hanging off of the edge of the plank.
Use saddle clips to place over the pivot bar at equal distances and fasten them into place. Take the three nails out after the pivot bar has been attached.
Insert two carriage bolts into the top drill holes depending on the height you would like the teeter totter to rest. Fasten the bolts into place with nuts.
Place the middle plank onto the pivot bar and position into place.