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.
Step 1: Lamination
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
Step 2: Trim Out Form
Remove the laminated wood from your formwork and marvel at your creation. You have completed the hardest part of the process, the rest is just detail work from here.
The laminated blank will be a little long on both ends and the edges may be a bit messy, so trace out your final shape with an offset in on all sides. I used a dremel to cut out the shape that I had traced on the blank. It is all up to good old hand eye coordination for this step, so be deliberate with your cuts.
After the final shape is cut out, I hit the edges with sandpaper to round them out. As a matter of fact, you may as well give the whole thing a light sanding to smooth it out.
Step 3: Mounting Bracket
To make the mounting bracket for my fender, I sacrificed one of my rear reflectors. looking back, I think I could have kept the reflector attached, but I liked the look of the minimal bracket on the fender.
I cut the metal bracket that attached the reflector to the rear brake bar with my dremel, and drilled two small holes in the bracket and the fender in order to bolt them together. I mounted the metal bracket about 1/3 of the length from the front of the fender, the end of the fender that doesn't curve out.
Step 4: Wire Brackets
In order to hold the rear of the fender stable, I made some wire brackets that bolt down at the hub and insert into the fender at the back.
I carved a small block with holes in it that are the same diameter as the wire. I glued this to the inside of the fender about 1/3 of the length from the back end of the fender. Keep the thickness of this block down as much as possible so there is no danger of touching the rear tire. I put a depression in the center of this block to further alleviate this danger.
Next I straightened out some wire hangers with a pair of needle nose pliers in order to make the wire brackets. at one end I made a loop that would be clamped down by my rear hub nuts. at the other end, I bent the end 90 degrees to be inserted into the mounting block.
Note: I have received some criticism from friends that the wire inserted into a wooden block is not a connection with a terribly long life span, but I couldn't help myself, I really liked the way it looks. Maybe try using a block made from a harder material, or maybe find a way to bolt the wire to the fender.
Step 5: Painting and Finishing
I painted on a rocketship graphic custom designed by Reid Cain of Dr. Cain's comics and games in San Luis Obispo, California to give the project a little more style.
To paint on graphics, I first put blue painters tape over the entire object to be painted, next I sprayglue a photocopy of the design onto the blue tape centered in just the right spot. I then cut out the design with an exacto and peel away all of the areas to be painted, being careful not to cut too much into the wood. I spray painted this graphic in first with a white spraypaint, then faded in a coat of red from the top and some black in the middle to give it a gradient. I then peeled away all of the masking and outlined the graphic in sharpie to make it pop a bit more.
I then finished the whole fender in a bunch of coats of polyurethane to seal it well. Sealing it well is very important as it will want to warp if it starts to absorb any moisture. I would maybe even consider using some kind of epoxy resin coating next time to be sure.
Step 6: Put It All Together!
Bolt down to the rear brake and bolt your wire brackets onto the hubs an you are officially riding in style. And with a dry butt.