|How I Built a Composite Bike
in my Garage
by Damon Rinard
This page is just a summary with ten images. After reading this page, you might want to read the whole article, which includes complete descriptions of how I handled the details. But that's just text, so be sure to come back here to see the photos.
Click on any image to view a larger version, then use your browser's Back button to return to this page.
This image shows the beginnings of the frame on its jig. The head tube area has the second lay-up of three or four layers of carbon fiber laid over the first. The first layers are cured, but the epoxy in these top layers is still wet. They will be wrapped momentarily with vinyl electrical tape to get them to lie down. At the right you can see the aluminum head tube (still extra long at both ends) and one of the many wooden stand-off blocks holding the tube above the jig. The wooden sticks are from popsicles.
This image shows the same area after I wrapped it with electrical tape. The paper below the frame is a full-size plot of the frame. In the larger view of this picture, you can see brown marker lines drawn on the paper. These are water lines, and they are level with the ground. I used them as references to take cross sections for checking the streamlined shape of the down tube.
This image shows the same area after I punctured small holes in the electrical tape to allow excess epoxy to ooze out. The wooden block is pressing some foam rubber into the concave area between the top and down tubes. Unfortunately, electrical tape can only compact convex shapes. In the larger view, you can see not only the excess epoxy, but also the drawback to using electrical tape to compact the lay-up: the slight waves the tape leaves behind. The flatter sides of the airfoil tube section get less pressure from the tension in the tape than the radii of the leading and trailing edges.
This image shows the rubber mold I made to shape the carbon around the dropout. On the left is the dropout. I show it covered with a thin layer of brown modeling clay which represents the thickness of the carbon. On the right is the rubber mold, a negative shape of the dropout. Wax paper is used to keep the clay off the workbench. Not shown are the clay walls I used to form the open-topped mold box into which I poured the Insta-Mold.
I am quite proud of this image. It shows the clay mock-up of the frame near the front derailleur. The silver part in the middle is the 1/8-inch thick aluminum backing plate that carries the steel front derailleur mounting plate. I should have used 1/4-inch plate, as the M6x1 threads in this one have stripped. (So far, my Helicoils are holding well!) I installed the derailleur on this plate to determine the clearance I needed in the clay. Just after this photo was taken, I poured plaster into this cavity to make a negative mold of these contours. After the plaster hardened, I used it to form a rubber "Insta-Mold" positive of this shape. Together, I used the plaster and the rubber to mold the carbon fiber patch that has the desired shape. After cure, I laminated the carbon fiber patch into the frame to define the frame contours around the front derailleur. The popsicle sticks are holding a cured carbon fiber "fender" in place. This fender defines the limits of clearance for the rear tire. On the chainstay, you can see a small piece of fiberglass (white in photo). I later laminated it between the aluminum backing plate and the carbon when I bonded them together. This prevents galvanic corrosion between the aluminum and carbon. In the larger view of the image, you can see the contours I wish the frame to have in order to clear the derailleur.
This image shows my front derailleur (it has the Kestrel 500 mounting plate attached), the aluminum backing plate and (from left to right) the plaster mold, the carbon patch and the Insta-Mold rubber mold I used to compact the carbon patch during cure. The layup to make this patch was like a temporary sandwich: the plaster was like one slice of bread, the carbon and wet epoxy were like the insides of the sandwich, and the rubber mold was like the other slice of bread. During cure, I squeezed the rubber firmly against the plaster to compact the carbon in between. To keep the carbon from sticking to the plaster, I first coated the plaster with a layer of petroleum jelly.
This image shows the first version of the frame mounted in my test fixture. I loaded the seat vertically to measure deflection. In the larger view, you can see the hydraulic hand pump and reservoir on the workbench to the right. The gauge is just out of sight where the hose leaves the pump. The hose goes to the hydraulic ram, which is hidden between the plywood reinforcements at the top of the fixture. There is no load applied in this picture. The nose of the saddle is tilted down because the ram slipped off the back of the saddle the first time I applied a high load. The vertical shaft goes from the seatpost binder, through the rear brake hole. The "tattletale" is white paper towel loosely taped with black electrical tape around the bottom of the shaft. The tattletale slid up the shaft as the beam deflected. Then after I removed the test load, the tattletale showed maximum deflection. You can see how much deflection I measured before this photo was taken.
This image shows the simple method I used to instrument the bike to record deflection while riding. As you can see, this method is very inexpensive! I later correlated these real-life deflections with the deflections I got from the known load I applied earlier using the hydraulic ram. This photo was taken before I recorded a ride, so there are no marks on the paper yet.
This image shows the finished bike. This is the first version. I tested this one to destruction in my fixture. Notice that the top tube has no taper. The diameter of the top tube is approximately the same at both ends.
This image shows the final version of the finished bike. I like this version much better. You can see how the top tube now tapers. It has a larger diameter near the front. The top half of this frame is new, and the bottom half is from the old frame. The overlapping bonded joint is in the middle of the down tube. In the larger view, you can see more clearly that there is only one left stay. There are two stays on the right. I like how the light in this photo shows the frame contours so well.
If you've read this far, you might want to read the long version of the article, including a complete list of materials, tools and supplies, and where I bought them (with contact information)!
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Last Updated: by Harriet Fell