How it works:
Basically, all it takes to make a carbon part is the right amount of heat, pressure, and time applied to the carbon “prepreg” that have been placed in a mold. If you have access to an oven, you have the heat source. Carbon parts can also be made with a “wet layup” approach in which dry tape or cloth is cured after the fabricator adds resin. “Prepreg” will usually achieve superior results compared to “wet layup” because the amount of resin is better controlled. Most composite “thermoset” (see definitions below) materials you might want to use for a bike, cure somewhere between room temperature and 350F. Carbon can also be made from “thermoplastic,” but that is tougher for the home fabricator, so we’ll not cover them unless someone requests it. A vacuum pump and bag can get you the pressure for many of these materials (think of a “seal a meal” bag). Any number of mold materials can withstand the combined heat and pressure for a small production quantity. The choice of mold material depends on how many parts you want to build. If the part is small enough, you could even use a toaster oven. On the other hand, if you want to compete with Trek, you’d buy large autoclaves and install stuff for mass production, with mold cost being secondary to mold longevity.
More than just theory:
You really CAN do this. In fact, people HAVE built carbon bikes at home. Go visit here, here, or here for their experiences. Arundel, a supplier of high end carbon items, and now, non carbon ones, started out this way.
Remember, if you are working with heat and pressure, you have the potential for some bad things to happen if any of this stuff gets carried away. Do NOT just plan on turning on your toaster oven out in the garage and come back the next morning to see your wonderful new carbon water bottle holder. You just might want to also read the MSDS on the raw materials. While they aren't going to be toxic, some people are sensistive and it's better to find out this stuff ahead of time.
Lots of Details I’m Not Telling You:
In truth, your garage is probably not currently suited to build composite parts, because the layup of these parts is completed in a “clean room” environment. Certainly, you can produce a “clean room” area in your garage, but it takes a bit of effort. It’s the same general idea as keeping dust off of a part that’s getting painted. Also, carbon “prepreg” is a bit spendy, so you don’t want to do a whole lot of trial and error. Fortunately, you can do some of the learning from books, and with fiberglass. If you’ve built a fiberglass boat, you understand many basic concepts. In addition, there are a lot of different places that sell this stuff. I haven’t purchased carbon composites from ANY of those below (at work, somehow the stuff just shows up after our purchasing experts do their magic), but there are hundreds more. What’s more, much of this stuff requires refrigerated storage until you are ready to use it, but freezers aren’t rocket science, either. Finally, there are lots of things you need besides the carbon prepreg itself – vacuum pumps, bagging materials, damming materials, mold release agents, and so on. None of this stuff is particularly expensive individually, but if you have to buy 100 yards of bagging material, it can be pretty expensive unless you have a plan to build more than a single bike frame. Let’s just say if you want to build the world’s most exotic carbon bike items, it’ll cost you more than if you were to take up embroidery as a hobby, but it IS within financial reach.
Clean Room – A location with active dust control and controlled environment so that a composite part may be fabricated without environmental contamination.
MSDS – Material Safety Data Sheet. You should read this whenever you are working with chemicals and stuff. It tells you all sorts of handy stuff, like if the material will kill you.
Prepreg – Prepreg is the combination of carbon (or fiberglass) fiber and resin that make up an individual layer (ply). Prepreg comes with the fiber and resin already to lay up. Prepreg is the preferred raw material for structural parts in which low weight is an objective.
Thermoset – A material that changes permanently when you cook it. Biscuits, for example, are a thermoset. You cook them and the dough changes to a biscuit. You cook them again and they just burn.
Thermoplastic – A material that changes when you cook it, but if you mess up, you can cook it again. Within reason, chocolate is a thermoplastic.
Wet Layup – Wet layup is a more traditional way of making mostly fiberglass parts, in which dry fiber has resin added to it at the time of layup. Typically, wet layup produces a heavier part than layup with prepreg since the resin content is not as well controlled. Wet layup is preferred when minimizing equipment and consumable materials is more important than low weight.
Any of y'all build your own "homebrew" carbon bike, I want to see photos!!!!!!!!!!!
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