If you have read anything about carbon fiber you probably have run across the term “pre-preg” but you may not know what it does or even what it is. Typically carbon fiber fabric is shipped as a dry loosely woven cloth. To use it, you use a variety of methods to apply wet epoxy resin to the cloth and then let it set at room temperature to cure. Pre-preg refers to carbon fiber fabric that is pre-impregnated with epoxy resin from the manufacturer. It is a thick material that you apply in layers to your mold. It is slightly sticky as well so it holds together and to the mold fairly well. Once it is applied, a special clear plastic sheet is applied over the pre-preg and affixed to the edges of the mold with a type of foam tape. This process creates an air tight seal between the inside of the mold and the outside. Next, an air hose is attached to the plastic sheet with a special connector and the other end of the air hose is connected to a vacuum pump. Once the pump is started it removes all the air from between the plastic and the mold “sucking” the plastic against the pre-preg and against the inside of the mold. What is really happening is that normal atmospheric air pressure is forcing the plastic and the pre-preg against the inside of the mold very firmly. Normal air pressure is about 15 lbs per square inch. Imagine that you had a 15 pound weight on each and every square inch of pre-preg, forcing it against the mold. As you can imagine, the pre-preg will have a very good fit against the mold. Because the air seal of the foam tape is not perfect the vacuum pump has to run continuously to ensure that pressure is always applied.

Now that the mold and pre-preg are ready, its time for the epoxy in the pre-preg to cure. Normally you mix resin and hardener together when you are ready to use it and it starts to setup immediately. Since the pre-preg came with the epoxy and hardener already mixed in, you need a different system to cure it. The answer is heat. All epoxies cure with heat, the question is how much is needed. Normal epoxies make their own heat when you mix the resin and hardener together. So long as they are used at about 70F degrees or so, the heat they create will be enough to cure them. The epoxy that is part of a pre-preg fabric requires much more heat, the heat from an oven. Once you have vacuumed the air out of your mold you put the whole thing in the oven to cure. Times and temperatures vary but its a couple of hours at 300 degrees or so.

And that’s how you use pre-preg. It makes the highest quality part because the mix of fabric to epoxy is always exactly right. Also, the fabric is more stable and you are less likely to have the weave disturbed as you use it. As you can see its more complicated and it costs a lot more too. But when you look at expensive cars like a Lambo or Zonda or even race cars, they are always using pre-preg.

Often, what you will really need is not a complicated curved part but just a simple flat sheet. Well, you can easily make a sheet with your Carbon Fiber Fabrication Kit. All you need are two sheets of glass slightly larger than the desired sheet. Simply prepare 3 CF sheets and two fiberglass sheets and some epoxy resin. Once you are satisfied that the glass is good and clean, I mean squeaky clean, lay down a layer of epoxy. You don’t want any gaps but the layer should be nice and thin, if you put too much is will just squeeze out and get wasted. Put your first layer of CF on the epoxy and without waiting for the epoxy to set up, brush on another layer of epoxy on top of the CF. Brush carefully as you don’t want to disturb the CF fabric. Then place a layer of fiberglass on the wet epoxy and repeat. Start out with 5 layers, 3 CF and two fiberglass. You can experiment with more or fewer layers but remember, to get a good firm board, you need it to be thick.  Another approach is to use a layer of corrugated cardboard as the middle layer with a layer of fiberglass and carbon fiber on either side.  This will make for a thicker, stronger sheet but it may be too thick for your needs. 

Once you have all the layers down and epoxy on both sides of all the layers, put your final piece of glass on the top of your stack and then add weights on top of the glass to ensure its nice and flat. Let it cure overnight, and in the morning carefully separate the CF sheet from the glass sheets. Do this very slowly by using screw drivers as wedges to slowly separate the glass from the carbon fiber sheet. You will see air slowly enter the sandwich with each new wedge. It is easier than it sounds but only if you go slow! Then trim the edges as straight as you can and you will have a nice firm piece of CF sheet

Some thoughts:
You can use window glass but it might be problematic as its very thin. There is a great chance that you will break it when trying to separate the sheets. Glass used for shelving would be better.

If you use the mold wax and PVA, it will make separation easier but even the thinnest layer of release was and PVA will leave an impression on the CF sheet. Epoxy doesn’t stick to glass too well and if your glass is thick enough, leave the wax and PVA off for the smoothest CF finish to your sheet. It may be a bit harder to separate but your results will be much better. If you try it, let us know how it goes.

Like so many people we think carbon fiber is cool. Its strength and light weight make it the first choice for manufacturers of race cars, high performance aircraft and even spacecraft.

Carbon Fiber is the first choice among builders of Formula One race cars, high performance aircraft, motorcycle racers, and even orbital spacecraft. Few other materials provide the combination of strength and lightweight that is so critical in making high performance components. By combining the latest generation of tough epoxy resins with loosely woven fabrics made from extremely strong carbon fibers, manufacturers are able to create parts that will withstand stress to levels never imaged from other materials of the same weight. Each passing year sees more and more products made from this incredible material. And lets not forget that it looks really cool as well!

The problem with carbon fiber has always been the complexity of making the parts and the cost of the materials. For years it required expensive components and special pressurized ovens to make carbon fiber and so only large companies willing to make substantial investments in tooling were able to create these products. If someone wanted to buy a part for their car or motorcycle the cost was usually extremely expensive if you could find the part you needed at all. But things have changed. Now there are epoxies that setup at room temperature with no loss of strength and if you look hard enough, the carbon fiber cloth can be acquired and reasonable prices. This is why we started this company, EastBay Composites. We wanted to bring carbon fiber technology to individuals who would like to make parts for their car or motorcycle out of carbon fiber but didn’t know where to start. We sell kits and replenishment components that make the whole process easy and inexpensive. Got a part you want to replicate in carbon fiber? No problem. Just purchase our ‘Mold Making Kit’ and you will have everything you need to make a mold of your part so you can make multiple carbon fiber copies. Once you have a mold then you are ready for the ‘Lay Up Kit’ to make your new part out of carbon fiber. We give you step by step printed directions as well as on video. All you need is a little time and a little patience and you can be on your way.

Thank you for checking out our site and our products. We think you will have a blast making custom parts out of carbon fiber. Enjoy!