Originally posted by Danneh
...can anyone give me any advice on how to repair composite frames ?
I haven't tried repairing a bike, but I've built and repaired a lot of composite structures over the years and I can't see why a bike should be any exception to the rule. First do a bit of research - try to find out more about how the frame actually is produced. What type of resin is it that binds the carbon fibre layers together? What other resins that can be handled outside a factory setting are there that can bond to the one they've used? If theirs is some sort of epoxy you are quite likely to be able to find a matching product. Even if theirs isn't an epoxy you might still find one with matching characteristics. A well equipped shop that caters to boat builders should be able to help you with both resin and some carbon fibre tape. Make a couple of "dry" runs by wrapping the the injury with another material or a length of fibre that you'll later discard until you've figured out how you're going to apply the "bandage", then prep the surface. You don't want to cut into the fibers too much, but run a fine-grit sandpaper over the damaged area and an inch or so on to the unaffected surfaces. Wash with a non-staining detergent and let dry (acetone should do OK). Mix up your resin, coat the prepped area (a brush is probably the tool of your choice here) and apply the carbon fibre tape as smooth as you can. When you've done one layer coat it with more resin until the surface becomes saturated, then add the next layer. Keep going until your satisfied with the thickness of your repair (2-3 mm should be sufficient depending on the length of the repair).
Some tips you might want to consider: Mix a small batch first and try different application techniques until you've figured out when the fible cloth is sufficiently saturated. For optimum strength/weight ratio you want as little resin as possible while still retaining full saturation, but in this case you shouldn't be too concerned about that.
If the salesman is unsure about material compatibility and bonding you might want to pick a small secluded spot on the bike and do a trial application. Prep a 1x1 cm surface, take a piece of carbon fibre (Several layers, fully saturated) and stick it there. Leave yourself a tab to pull with. Once the resin has cured properly give it a good pull and see what happens. If the pull is parallel to the treated surface your grip (even with pliers!) should slip before the patch breaks free.
Disclaimers and warnings: Epoxy is toxic. Protect your skin from spill and your airways from fumes. Wear gloves and an approved mask.
The accident might have damaged your bike in some other place that you haven't discovered yet, or your repair might not be as good as you thought. Inspect it CLOSELY for other damage prior to repair. After repairs start with easy rides and inspect after each one. Be attentive to how the bike handles. Any further deterioration needs to be taken very seriously.
There's a site somewhere that describes how to fix a broken carbon fibre saddle, it might serve as some inspiration if you can track it down.
