Carbon fiber frameset construction

A very pair of chainstays (35.6 gms each),

The chainstays have been taken out of the mold.

The mold is closed on itself after enough carbon fiber has been used for the piece. This is what the chainstays look like after being removed from the oven,

The mold is made once the design has been finalized. The mold itself is split in 2 halfs which will encapsulate the piece that is being made. The specs need to be very exact since the quality of the piece will depend on how well the two halfs fit. The mold is covered in both halfs with pre-preg carbon fiber, in this case, unidireccional. The photo below shows how the mold have been lined with carbon fiber,

Hello everyone. Now I would like to show how I make the chainstays and the rear brake bridge using molds. Molds can be made from different materials. In this case, I used aluminium. To make a mold, you will need a mill so an aluminium block can be cut, shaped and polished to the shape of interest, in this case, a pair of chainstays. The shape of the chainstays can be designed using a CAD program as shown in the picture below,

A very strong and light set of dropouts,

The dropouts further along,

The carbon sheet is now placed on a CNC cutter and the dropouts are cut,

And this is how it looks once cured and all the vacuum bag material discarded,

Subsequently, the plate is placed into a vaccum bag and sent to the oven for curing

Hello everyone. I'm back. I shall continue with my story. Now I 'll show you how I do the dropouts. The first step is to create a sheet composed of several layers of carbon fiber. Once cured , this plate will be about 3 mm thick, enough to draw some very strong and super light drpouts. The photo shows how the different layers of prepreg carbon are placed on top of an aluminum plate which has been previously polished and coated with release agent.

In my next "chapter", I'll show you how I make chain stays, dropouts and the rear brake bridge, all out of molds. See you soon.

And this is the 3 main tubes look like once baked and removed from the vacuum bag. As you can see, the surfaces of the tubes are a bit rough. This is due to the type of material used for wrapping the tubes for curing. This is dealt with relatively easily by subsequent sanding but I am in favor of sanding as little as possible because, invariably when sanding, carbon fibers are broken and, in a way, the integrity of the tube is compromised. Now I'm trying molds that will leave an outer surface of the tubes completely smooth. The last step is the removal of the aluminum mandrel from inside the tubes. This is done very easily if you have cleaned the mandrel with release agent before the wrapping of the carbon strips. If you forget this step, then I can assure you that you will never be able to take off the mandrel form the inside of the carbon tubes.

The tube is then placed inside a vacuum bag and subsequently cured in an oven. By the way, I almost forgot to say that I only use carbon fiber that has been pre-impregnated with epoxy resin (pre-preg) as it facilitates the handling of the material lot.

This is the final result after wrapping all layers,

To begin the construction of a carbon frame, I'll show you how I make the main tubes (down, top and seat tubes). I use a mandrel which is just a solid aluminum cylinder, the diameter required on each tube and wrapped with strips of unidirectional carbon fiber. I use unidirectional carbon so that I can control the direction of maximum tensile strength and compression (that is the direction in which the filaments of the carbon fiber have been arranged). This results in different layers wound on the mandrel with directions ranging from 0 °, + 45 °, -45 ° to 90 °. In this way I make sure that the tube will respond well to forces in tension, compression and torsion (with the fibers at 45 °). In the picture below, you can see how the strip 45 ° is wound onto the mandrel.
 

Hello, I build bike frames made out of carbon fiber. I would like to show the process that I follow to design and build such framesets. I'm about to finish a road frame and I will be posting notes on how I'm progressing (including photos). I hope it is informative for you and I hope I can also get help from some of the members of this forum.