First off let me give props where they are due, this idea was inspired largely by the instructable posted by mydian_nightshade called Cheap bike rack. Please visit his piece to fill in any gaps on construction or to see what else can be done using this same process. My documentation was done without a step-by-step in mind so it is a little dicey, however the process is very simple and fairly self explanatory. So, lets get started.
Dollar Store LED flashlight
Stain (if desired)
Tools; Table saw, chop-saw (miter saw), chisel, drill, sander
Step 1: Getting Started
The first thing I did was rip the 2x4 lengthwise on a table saw to get two 2x2 sticks. Next, you need to measure across the frame, starting a couple of inches behind the top-tube and extending out to the distance you want your rack to end. I decided to make a rack that would extend the length of the tire and came up with about 21 1/2 inches. Cut two sticks out of your 2x2s to the length you like. These are going to be the center pieces of your rack and they will sandwich around the frame. To achieve this you simply need to hold the pieces, one at a time, up the the bike frame at the height you want your rack to sit, and trace the frame onto the wood. Use a level to insure that your rack wont be tilted up or down when you are finished. This is the shape that you need to chisel out to fit the boards around the frame. If your tubes are 1" in diameter then you would cut each board to a depth of 1/2". (again, mydian_nightshade has a great example of how to do the chisel work HERE It helps the stability of your rack if it is a tight fit, so it is better to err on the side of removing too little material and then fine tuning the fit from there.
Step 2: Mounting the Rack
You may want to cut an angle on the back of each center piece so that they come to a point, I used a chop-saw to do this and it ended up providing much needed knee-clearance for such a small bike. After you have your boards ready to go, simply fit them in place and screw them together. I put one screw behind the top-tube, one through the middle section, and two through the front. As always, use pilot holes to prevent splitting your boards. Next, cut two more lengths of 2x2s, shorter this time, to create a wider platform for holding your stuff. Once again I tapered my boards for aesthetic reasons but this is a matter of taste (looks kinda like a paddle, eh?). Screw the side boards to the center pieces. I countersunk my screws and used wood putty to cover the holes, however, if you want your rack to be easily removed you may forgo this step. After a quick sanding to ease any rough edges you can stain, seal, or paint the wood to your liking.
Step 3: Installing the Light
To install the headlight I took an off-the-shelf LED booklight from the dollar store and striped away all of the superfluos plastic until I had a neat cylindrical light to work with. Starting small and working my way up, I bored a hole in the front-center of the rack large enough to fit the light in, and just deep enough that when you pushed in on the light, the switch on the back of the unit would depress and turn on the light. I made a paper tube to line the hole so that the light wouldn't get stuck on the rough wood when you click it on. Next I cut another piece of wood out of one of my remaining pieces of 2x2 to act as a faceplate and hold the light into the rack. I drilled a hole through the face plate that was large enough to acomadate the light on the inside, but small enough that the light cannot fall out of the assembly. Screw it on. Now all you have to do to be street legal is push on the light and you're all set!
Step 4: Finishing Touches
I have been extremely happy with this rack so far. it has held up perfectly, and can hold a full load of groceries or a fat stack of textbooks. One of the biggest benifits for me however, has been using it to hold my bike lock. Using a Bus-fuse clip and screwing eyelets to the bottom of the rack to accomadate bungee cords, the rack fits my U-lock perfectly. It is strange at first having a rack that doesn't turn with you when you turn your wheel. The rack floats out in front following the frame, but it is actually quite cool once you get used to it.
Thanks for reading! Don't forget to vote in the "Light up your Ride" contest, and please send me some pics if you decide to build a wooden rack!