Bend the long side of a 12-by-14 inch L bracket at a 90 degree angle using a pair of pliers.
Make the bend two inches in from the edge. When completed, you will have a C shape with two 12-inch sides and one 2-inch side. If the bracket is particularly hard to bend, place it in a vice grip first, then bend the end.
Place two 12-by-1-by-2 inch boards on top of one another in an X shape.
Use a drill to make a hole through the center of the X. Insert the 1-inch bolt through the X. Place a nut on the bolt and tighten it as tight as possible to secure the boards in place.
Hammer in a 3-inch nail, centered on the end of each board.
Leave the nails sticking out 1-1/2 inches from the end of the board.
Pass the end of the bolt from Step 2 through the hole in the bent end of the L bracket.
Place a nut on the end of the bolt. Tighten the nut. The bolt should still be able to spin on the L bracket.
Attach the L bracket to the side of a tree using three 3-inch nails.
Choose a straight section of the tree to help prevent the squirrels from hitting the tree trunk when the squirrel-a-whirl spins. When attached, the 2-inch side of the L bracket will be parallel to the tree trunk.
Place the end of a dried corncob on the end of each nail that is protruding from the each arm.
If necessary, use a hammer to force the nail through the end of the cob.
Replace the corncobs, as needed.