Well, unless you have bad eyesight or didnt see my last post, I'm working on making carbon cantilever brakes. I got one arm nearly finished (all thats left is to spray it with a clear coat). I wanted to have them done by today and to have some pics for the website, but I ran into some problems...
...My first mold that I made was all wrong. And I didnt realize that until I took the carbon out of the mold. And started looking at it (you can see the inferior prototype in the main picture of my drawings--its sitting off to the side of the picture).
I went back to the "drawing board" and produced the designs that are pictured in the first post of this little "series". Those drawings resulted in a second mold, in which I was trying to create both arms at the same time, saving time and money. But, that didnt work out so well and I had to sacrifice a good deal of material just to get one arm out of the mess (when I pulled the carbon off of the mold, it pretty much destroyed the mold itself).
So I had to make another mold (#3), and I layed up some carbon yesterday to make the other arm. Unfortunately, its 50 F here in Sacramento and I didnt add enough catalyst to get the resin to harden. I tried everything too (heat lamps, kept it in the vacuum bag all day (like 9 hours)) and by night, I had to throw the wet carbon in the trash.
Today, its the same temperature outside, but I added about 5 times the amount of suggested catalyst, brought it into the garage, with a heatlamp on it again, and this time I think its going to work. I've taken it out of the vacuum bag and into the house where I think its going to dry and cure just fine. Basically, you cant take it out of the vacuum until the resin sets enough to hold the shape of the mold.
Another tricky point of the process was finding a tube that would slip over the brake post for the cantilever to pivot on. This had to be just the right size or else there would be major play in the brakes. I tried a lot of things, plastic spacers, premade fiberglass/carbon tubes, brass bullet casings, and even considered making my own carbon tube. Before I found a brass tube at my local Ace hardware store that had the perfect internal diameter.
I am going to also be making the end nuts I believe. I could buy the Empella nuts, they are $20 for a complete bike (not a bad price) but they are sold out at the present time, we'll see. The brake arm made currently weighs 12 grams without brake pads.