In order to build a backyard swing arbor, you will need the following: 2x4s, 1x6s, a bench swing, 4x8' sheet, a drill, carriage bolts, galvanized nails, and screws. Cut 4 2x4's to 87". Cut a notch 3.5x1.5 in each, at the corners. Cut 2 2x4s to 15" each. Lay the 87" out on a flat surface, in a parallel fashion. Lay the connectors across the top of it. Align the notches. Make sure the sides are flush. Drill holes through the connectors. Drill holes through the base and connectors. Attach the boards with carriage bolts. Cut 2 2x4s to 48". Fasten the feet to the uprights. Cut 2 16.5" support pieces. Screw them to the feet. Cut an 8" support for the feet. Fit these to the top of the main foot. Always make sure that everything is flush. Make braces by cutting 8 1x6 boards. Make sure that the braces are 27" between the longest points. You will need to bore holes in the ground to stabilize your swing when it is completed. Drive rebar through it to stabilize it. When the frame is complete, attach the swing.