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So, I have a frame with cracked/broken top tube - near the seat tube junction, about 2/3 of the way around. It's definitely broken though it seems to be holding together quite well due to the loads on the bike mostly compressing the tube in that area, except when you sit heavily on the saddle. As such, it's not something that's likely to fail disasterously or unexpectedly (giving that it's holding together right now with only a small part of it actually connected).
A replacement is on the way, but it seems a shame to bin the frame and tbh I quite like the challenge of this sort of thing so I reckon I'm going to give it a go at repairing it, particularly as I know other repairs that have lasted many years and are still going strong - one of the big positives about cf repair - do it right and it's very strong.
So, my plan is to get one of these kits (this is what they recommend for repairing bike frame tubes)
http://www.carbonmods.co.uk/Products/fishing-rod-pole-repair-kit.aspx
I'm pretty comfortable with the process but I do wonder how much carbon I should use and how to place it.
The obvious is to just wrap the cf ribbon around the tube and so long as the surfaces are properly prepared, then that should provide sufficient purchase to hold it in place.
I have considered wrapping the cf around the seat tube but that seems only necessary if you feel that it won't adhere to the tube otherwise.
And then how much do I use? 3 wraps? 5? 10? Anyone got any idea of the loads on a TT at that point or what number of plys frames would typically have there (and I know it'll be dependent on the strength of the particular cf I use but I should be able to find that out).
TIA. Consider this an experiment or part 2 of CynicAl's cf experimentation 🙂
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hth.
😀
I don't believe that I will need any cutlery for my repair 🙂
maybe a spork?
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Only if it's Ti 😉
Have a look at the carbon frame repair websites, a few have pictures of the various stages. It seems the jist is to just cut the damage back, bung a load more carbon on and tidy up after. For a nice finish it needs more work but even a basic bodge looks ok once smoothed.
The fishing rod repair works for smaller cracks, not certain I'd use it for a large circumferential crack though.
That said, my repair was using that kit on a longitudinal crack near he BB. I think I placed about 4 layers on, first aligned across the way, next at 45 deg to taht, then 90 deg to that, then another across the way.
I also wrapped in some around the BB junction to add more material and 'tie' it to another area. I'd suggest it'd be worth doing that around the seat tube is you can.
They do a bike repair, which is tougher cloth and I think comes with a bit of powder too so you can fill and smooth once done.
Mine is a bit of a crap job, strong enough, but not tidy. Was riding it the day after the resin cured 🙂
I've been doing that. This is quite a good guide:
http://www.instructables.com/id/Repairing-a-Carbon-Fiber-Bicycle-Frame
It still doesn't really answer the question of how much carbon to use though...
Are you going to cut completely through the tube ?
I would be tempted to cut right through, slip on a biax tube sock or 2, along with the Heatshrink, then epoxy a new carbon tube inside the frame tube across the cut. wrap carbon tape around the joint, then cover with the Biax Socks to make a nice finish.
cover with the heatshrink to consolidate the joint
Thanks wookie - I was wondering about a cross ply layup rather than a simple wrap and then whether 45 degrees is the ideal layup - I was thinking that 60ish with the main length of the fibres along the axis of the tube
cr500 - I hadn't intended to if not necessary (given that it holds itself together most of the time) though it could be an option - that said, it's not actually very round - quite ovalised (so narrower when viewed from the side of the bike) which would make fitting a new carbon tube inside tricky.
wookie - have you got a link to the bike repair kit? I can't find it.
looks like the heavier duty one has been removed. hey ho. here's something similar:
[url= http://www.carbonology.com/kit-no-2b-the-bike-frame-repair-kit-p-240.html ]repair kit[/url]
Are you going to cut completely through the tube ?
This is a good idea imo.
I was going to suggesting a gusset of metal underneath it and glue/screw it to the underside of the tube, but this is a good idea. Also see if you can fill the tube end with a plug of something so that it doens't deform either when you do the fix or when it's under load. Not so easy if your tube is not round in profile though.
Although if you are going to do that you could put a bar in joining the two pieces to gether internall as well as externally, but that'd require a lot of flex to be able to add the piece.
Why is it a good idea? Unless you cut a whole chunk out of the frame, in which case your fix becomes rather more structural!
I'd just go for the 'wrap a few layers' approach, no point turning a crack into a massive gaping hole in your TT IMO!
PS I should apologise.. all of what I said was already mentioned.. I should learn to read.
just wrap the lot seat cluster everything ,daub it on
sand it back so it looks nice...this is how the pros do it right?
Did it break in normal use, or in a crash? Before doing any mend, I would want to understand what the stresses on the mended area would be.
My mates top tube cracked he took to a fishing pole guy in Peterborough £25 its been raced rode hard for 6 months now and is fine.
It broke in normal use.
I'm actually not going to be repairing it now - the company who sold it to me have asked me to cut out the whole cluster and post it to them (which they'll pay for) to see how it failed - first one apparently.
I guess we'll see once I get the replacement whether it's a one off or
a consistent issue.
Back to the repair method though, I think that keeping it together would have been the option in these particular circumstances - alignemnt won't be affected and since it's not totally separated at the moment, there's at least some structural strength provided by the section where the crack is when in compression.
This a Chinese direct company? Sounds like good after sales service if it is
Yes, it is and yes, they've been pretty good - they asked for photo of the damage and the whole bike (I assume to check I hadn't done anything silly with the build) and then within a couple of days told me they'd send a new one. Only downer is that they don't have stock so it's about a month for my particular model/finish.
Slight hi-jack, I have a cracked seat tube - hairline crack (definitely not just the lacquer) about 2" long running top to bottom.
Assuming you could accurately locate them, would you drill the ends of the crack before wrapping?
That was certainly what I was planning to do.
I fixed a cracked Seatube on a Roadbike frame (had it welded once and managed to crack the weld) with Carbon repair kit - been riding it nearly a year now and it's going fine. The Australians used a similar thing to fix a Warship so for a bike frame it's ugly but usable.
Which company Clubber? That's impressive service even with a delay for stock
Agreed, can't argue with that!
Miracle/Ican via Aliexpress - the company that most people recommend as having been around for a while and producing good quality frames. I read up a lot before parting with any cash and they seem to consistently be good with customers.
The only issue I've had with them was that they changed their email address between me buying the frame and having the problem so it took some time to get in touch (because I didn't know they'd changed email address) but once I got hold of them, they're very responsive - usually within the day (time zone depending of course).
have you got a link, i can't figure out how to search for a seller on the Aliexpress site
Miracle/Ican:
http://www.aliexpress.com/store/409931
http://made-in-ican.en.alibaba.com/
New frame should now be on the way to me (delay due to no stock of my size and frame finish)