Step 2: Cut Some Plywood
In order to get an even bend, the pieces should roughly have an even width. The rear wheel section has a fork with two 1 1/2" wide sections that are 3 3/4" apart. The rear forks are 13" long, and they narrow to 3" apart where they join together. It thens tapers down to a single 3" strip. The total length is 43" The dimension don't have to be perfect since I will shape the frame once it is all glued together.
I only cut 4 pieces to start with. Two of them are a 1/2" longer to account for the extra length needed when bending. Small holes are drilled into the ends of the boards so they can be wired together. The two outer boards have the holes an 1/8" further from the edge so they can line up with the inner holes, and still come together at the end.
Wire up the boards and see how the ends look. For wire I used 18 gauge solid copper wire. At this point I had to cut a little bit off the ends of the outer boards to make sure they came together like I wanted. A temporary seat tube is made out of a piece of PVC with fabric taped to the ends to prevent it from slipping off the plywood. The fabric adds some friction to keep the tube in place, although it still slips off more often than I'd like.
Several times I held up the frame to my old $99 cheapo bike to see if the dimensions looked right. Once the frame is the right size, I cut the glass fabric to the shape of the boards.