To make a cheap motorcycle frame, create the design of the motorcycle, cut steel tubing to desired lengths, weld the top frame, weld the lower rails, and install the neck gusset, seat post and cross braces. Attach clips and mounts. Wear protective gear to protect your eyes and hands from welding sparks.
Sketch the design you want on a piece of paper, making sure to specify measurements and angles of all parts. Use a chop saw to cut steel tubing into neck stem, bottom rails, top tubes and wishbone tubes. Be sure to use tubing with a 0.125-inch wall and 1.25-inch diameter. Cut other small tubings for the seat post, neck gusset and crossbraces.
Bend the wishbone tubes and bottom rails with a pipe bender. Use a welding gun to weld the top tubes to the neck stem, and the wishbone tubes, under the seat, directly to each other. Then, weld the wishbone tubes to the top tubes and lower rails. Bend the bottom rails, leaving enough space for the engine, gas tank and battery. Weld the rails to the neck stem and top tubes.
At the front of the bike, weld the neck gusset to the top tubes, securing each side of the tubes with neck gusset plates. Install crossbraces beneath the seat section and at the center of the lower rails, and then insert a transmission plate between the crossbraces. Weld the seat post between the wishbone tubes and the top tubes. Use a 1/2-inch spade bit to drill holes onto the frame, and attach clips and mounts as desired. Smooth the joints with a sandpaper, then paint.