Repairing a CF frame – how hard can it be?
How will you cure the pre-preg. Have you a large oven? I’m not sure how long it will take at room temperature.Posted 5 months ago
Also, the new carbon and epoxy isn’t going to be well fixed to the existing carbon, so is likely to be weaker. I’d either pay the money or cut it up to see how it’s made (my choice!).
My cycling buddy has a Tarmac SL4 frame with the RH chainstay crushed for 50% of its circumference over a 4″ length from where he and a car had an unfortunate meeting (both agreed to share the blame). He got a new bike on his household insurance and is loathe to throw away an otherwise perfectly good frame. Repairs are going to cost between £200 and £350 according to a couple of repairers we’ve called.
How hard can it be to repair at home using pre-preg wraps and being willing to live with a slightly fatter tube? I’m not sure how we could rebuild the tube to the same diameter because filling with foam then wrapping seems to be a standard repair but there’s the problem of the RD cable inside the tube.Posted 5 months ago
The chainstay is crushed but only the outer 50% of it is actually cracked, so if we cut out the damaged section we would still have the inner half of the chainstay. My understanding is that conventionally you would fill the tube with a foam, then feather the edges of the hole and wrap it with carbon going in different directions before wrapping very tightly while it cured. My concern is the internal cable – I guess we would have to fit a tube inside the stay for the RD cable to run inside.
We have an Aga so I guess leaving the frame on top of that overnight would be warm enough – or does it require intense heat?Posted 5 months agoPaul@RTWMember
I fixed my stereo seat stay with ‘cold-cure’ resin and cloth. It’s still going strong many riding hours later – 2 years worth, I think.
I build and ride whole frames using the same techniques (as have a few others on here).
I’m sure I’ll die in a fiery of death but in the mean time, happy to answer any questions – email in profile.Posted 5 months agorollindoughnutMember
I repaired a carbon wheel with glass cloth and West epoxy. Still use it regularly.
Also have repaired around the bb area on another bike and numerous windsurf boards too.
Get nice fine cloth from a model shop carbon or glass. Lay it up using a paint brush to squidge the epoxy into the cloth then wrap it in a bit of carrier bag (epoxy doesn’t stick to PVC) and finally apply pressure by wrapping tape around it all.Posted 5 months ago
Leave it for a day in a warm place, then sand it all down for neatness.
I’ve thought about this, especially having seen how cheap high end broken frames go for…and given my carbon expertise (IT WASN’T A SPOON).
If you have to entirely cut a section of tube away, I think it’s be tricky to effect a neat repair, esp with an internal cable, but surely you could create a former using expanding foam over tubing, leaving a space for the cable?
Physically joining would be tricky, I’ve thought of tapering the “good” ends of the tube, drilling holes into the taper, then putting ball bearings or similar in between layers of your repair wrap to force it into the holes, creating a physical join.
Not sure evening would risk it on a chainstay though, it’s one of the most stressed tubes on a bike (in stark contrast to a seat stay).
The Pinkster – Member
If a chainstay has been damaged I’d be concerned about wheel alignment
If you’re not confident checking this as you go, then you shouldn’t be attempting this repair IMO! I think it’d be easy to get right.Posted 5 months agocookeaaSubscriber
One technique I’ve seen (in a Video on youtube IIRC) was to make an external support out of a single layer of thicker/denser Woven carbon (600g/m^2 or higher), as it’s thicker and less compliant you can wet it out and place it over the damaged area/hole and it takes on the curve of the tube wall just to bridge the damaged area, allow that to cure, sand it back, and use that as the support for the final structural reinforcement which will extend further either side of the damaged zone. You could just use glass fibre mat or Another option might be to construct an initial support by winding Tow over the damaged area, allowing that to cure and again using that as the support for a larger repair ‘splint’…
You just want something that’s going to resist compression on the final repair, if you need to maintain a hollow tube you don’t have to use a foam core, of course yet another option is to use a foam core, and then melt it out afterwards (using Acetone IIRC) assuming you can get in there (through the BB?) to do it…
Where there’s a will there’s a way…Posted 5 months ago
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