Although Wilbur and Orville Wright designed their airplanes, they did not necessarily build every single part themselves. Dayton's West Side was a beehive of machine shops and manufacturers, and the Wright brothers took advantage of these resources. They "farmed out" the engine castings, some of the gears in the engine, the bent wooden pieces, and many other parts to local  businesses that were better equipped to make them than the Wright brothers themselves. The completed Flyers were a product of the Wright's genius and the local talent that was available to them.