bike rack manufacturing

After the initial design and measurements comes the fun part -- prototype manufacturing. I decided to go with .25" birch plywood for the material. I had plenty of it left over after a recent kitchen cabinet remodeling project. It's close enough in thickness to the 3/16" aluminum plate that I intend to use for the final product, is quite forgiving and easy to work with. Best of all, I can cut it with a 1/4" router bit to full depth in one pass. This makes prototype building quite rapid. The final product, on the other hand, will be cut by the same size endmill, but in multiple successive 0.05" deep passes with a final cleanup pass, making the machining much slower.

Here you can see a partial prototype made of plywood. The goal was to have the rack as low as possible so I could still use the grab bar for it's original purpose. Furthermore, I wanted to rack to be slanted just a few degrees forward when my full weight was on the seat. The easiest way turned out to take a rough plywood model, mount it to the bike, sit on it with my full weight, take the final measurements using a small level, and adjust the model accordingly. When my wife is on the bike behind me (2-up riding) the rack is perfectly horizontal.

After final adjustments are made, the real manufacturing begins. Here you can see one of the side brackets being milled.