I made this simple laminated plywood bike fender a few years ago for my beat up old road bike (one too many soggy butt rides) This was a perfect weekend project for this bike loving DIYster, made of inexpensive materials and relatively easy to assemble.
I added a graphic on the back for a bit of flair, a rocketship designed by the fantastic Reid Cain of Dr. Cain's comics and games (http://www.yelp.com/biz/dr-cains-comics-and-games-... Thank you Reid!
Note: This was my process for the project, which is always highly dependent on what materials/tools are immediately within my reach. Some of these steps may be completed in a much more efficient manner, please feel free to modify this process as needed to better fit the materials/tools that are within your own reach.
To start off, I established the radius of my fender. To do this, I measured the distance from the center of my rear wheel to the bottom of the horizontal bar that my rear brakes are mounted to. This is where the fender will be mounted to the bike frame.
Now I transferred this radius to some scrap 1/2" OSB using the old string method, this will be the formwork for laminating the fender. First I stuck a pushpin into the OSB and tied a piece of string to it (be sure to use a string that doesn't stretch). Next, I measure out the previously measured length on the string and tied a pencil to that end. Using this as a compass, I traced out a semi circle of the correct radius. I traced out about 1/4 of a whole circle, but this is a matter of aesthetics. The larger the arc, the farther it will come down your back tire. I added a little swoop at the end of the arc to give the fender a flare at the end.
Using a jigsaw, I now cut a big messy oblong oval around the traced arc, offset 3 or 4 inches off either side of the line (see images for reference). This was a necessary step in order to allow for the limited size of my wood clamps. I then cut out two more rough ovals and glued up the tree pieces to get the thickness I needed for the formwork.
Once the 1.5" thick OSB oval block is dry, I cut along the the pencil line with my jigsaw, being very careful to make a clean, smooth arc. At this point I had the formwork that you see in the pictures. I added a couple of strips of duct tape to the inside edge of the formwork to soften the clamping slightly.
Next pick a hardwood veneer to laminate for the fender. I ultimately ripped and planed down a piece of hard wood scrap from my school shop into three 1/16" thick strips. I'm not sure what type of wood it was, but I liked the light color. Maybe Birch, or Beech, or oak?
Next I slathered wood glue on one side of two strips and two sides of the third and smushed them all together. Putting wood glue on both sides that are being set together helps to guarantee full adhesion, more glue is better than not enough, the excess will be squeezed out by the clamping anyway.
now set the glued up strips into your Formwork, and clamp it all together. Forget about the whole setup for a day or two while it dries