Tell If Carbon Fiber Bike Cracked
Founder - Brady KappiusI started experimenting with composites in high school with my dad. As lifelong cyclists, we saw the increased use of composites in the cycling industry in the early 2000's and wanted to learn more. I followed my dad's footsteps and attended the Colorado School of Mines while still focusing on my cycling career. After turning professional, I attended the University of Colorado to pursue my masters and founded Broken Carbon at that time. I had a few people come to me looking for repairs and through word of mouth, Broken Carbon has just grown from there! Engineer - Cameron FrazerWith my Masters Degree in Composite Engineering I assure all repairs performed here at Broken Carbon are of high quality.
Designing a repair from a structural point of view is not trivial, and no repair is identical. Different types of repairs require not only different types of 'layups', but they also require different methods of manufacture to replicate the original laminate.
One fine morning I was riding up the mountain and I guess I was pedaling too hard or something.Somehow — and we're not precisely sure of the precise sequence of events — it seems that I managed to break the bike chain. The broken chain then got itself entangled in the rear derailleur. Since I was still pedaling, fairly hard, this caused the rear derailleur to be ripped from the frame.All of this happened within the space of about a second. The next second would be even more exciting.Since I was still pedaling, and the chain was still on the front chainring, the derailleur was then dragged through the narrow space between the rear wheel and the right-side seatstay.
Since this part of the frame is a crispy brittle carbon fiber tube, the derailleur managed to take a nice chunk of tube with it as it went sailing past.This is an interesting bit of damage. I'd never seen it before and although the bike, after a bit of chain tool activity, was still seemingly ridable, it was difficult to know exactly how dire a problem it was. Unlike steel which will bend considerably, carbon fiber tends to fail all at once and catastrophically. So it's a safe conclusion that this is a big problem.The internet wasn't terribly helpful. Apparently, this is not an uncommon thing. There's a company outside of Santa Cruz called Calfee Design which seems to do almost all the repair work for everybody and everybody seems to recommend their work.
Sadly, their work starts at a $300 minimum, requires the entire frame to be stripped down and shipped, and they don't make any particular guarantees.The first bikeshop people I talked to were anxious to sell me a new bike. A friend who knows a thing or two about frames said to chuck it and buy a new frame.
Trek, the company who made the frame with the brittle part right there in the derailleur flight path, would happily sell me a new frame through their 'crash replacement' program which borders on a complete scam and briefly made me hate them.Things weren't looking good.Then I ran into James at the Missing Link bike shop in Berkeley. While everyone else had been pessimistic and dour, James was brim full of gung ho. And while he had no actual personal experience in this department, he knew someone who had heard of someone who had done it himself.Good enough! This was precisely the encouragement I needed. So I rolled the bike home and set about figuring out what I'd need.The entire project took three days, almost all of that spent waiting for stuff to dry.
Materials mostly came from TAP Plastics, a local chain selling all kinds of fascinating and deadly polymers. There's a large selection of cheaper alternatives on the internet but I wanted to get this done in a hurry.
You probably have a similar place in your nearest large urbanization.What follows is a set of photos and notes on the process. I hope this is helpful. As far as whether this is a safe or effective way to repair a frame, you're on your own. Seek the advice of a qualified professional.
I am neither. Now to start patching the hole. The idea is to fill it with epoxy, let that cure, and then sand down to a smooth surface which will then be wrapped in fiber.The epoxy and filler come from a local epoxy and filler shop. There is infinitely more of each than I'm ever going to possibly use but these are the minimum quantities available.
Total cost was a little under $50.What we're looking at is a large round bottle of marine-grade epoxy resin, a small round jar of 'cab-o-sil' filler, and a smaller rectangularish bottle of epoxy hardener. Epoxy resin is a magic liquid that stays liquid indefinitely. Until you pour some of that hardener liquid into it.
Which starts a crazy exothermic (ie, gives off a lot of heat) reaction that quickly results in a hard, solidified resinous mass. The speed of the reaction is determined by the types and amounts of epoxy resin and hardener used. Generally, the slower the hardening, the stronger the eventual bonds.There are trade-offs to be made in the choice of epoxy resin. Some are stronger than others.
Some dry clearer (as opposed to browner/yellower). For this job, I wanted the strongest I could find. But I also wanted as colorless an end-product as possible (because I was attempting not just a mechanical repair, but an aesthetic one as well).
I ended up looking through the catalog (where these qualities are listed) and picking a resin that seemed to be good enough in each department.And this 'cab-o-sil', what is it? The label says 'fumed silica'. A white fibery powderous substance that is probably hell on a lung.
Make sure you're wearing a dust mask. It's here to give the epoxy some body so that it can be stuffed into the hole and stay there. The other option would have been microspheres. Which are these tiny, bigger than dust but not much, hollow glass bubbles that do roughly the same thing. The difference seems to be that the bubbles produce a much lighter solid while the silica produces something a little stronger.
Tell If Carbon Fiber Bike Cracked Download
Proper tradeoff? I don't know. The internet sez microspheres, the plastic shop guy sez cab-o-sil, and the price is the same. Since we're talking milligrams here, I go for the silica. At this point the plan is to goop a healthy amount of goop into the hole and past the hole into the tube. Let it harden and then sand it down smooth.
In theory, this should give the new fiber a smooth surface to bind to. And should stabilize the ragged edge of the damage.Is this the right approach? It seems like it but often these things have a way of being completely counterintuitive. It could be that by loading the tube at this point with a stiff epoxy will concentrate stresses at some other point, simply moving the failure to a different part of the tube. Or maybe not.Plus it's hard or impossible to tell what stresses and strains this particular tube sees in action. I'll bet there's a mechanical engineer with a masters degree in exactly this but that mechanical engineer is not me.Working out the physics of a static load on a bike frame isn't too difficult.
But where's the fun in a static load? Once it starts moving everything gets awfully complicated. And all of the obvious simplifying assumptions (the chain pulls the center of the rear axle, the rider's weight is always on the pedals, the bottom bracket isn't flexing in three axes, the road is smooth, etcetcetera) all of them seem likely to also be wrongifying assumptions.So I tape off everything around the hole. The epoxy is mixed 4:1 with the hardner and then I added the filler. Enough to get it to about a peanutbutter consistency.
Once mixed, there's oh maybe 15 minutes before it heats up and solidifies. Which seems like it should be plenty of time but almost never is.This is hundreds of times more glop than I'm going to need. But it's fairly difficult to mix up small amounts of epoxy with any accuracy. And if you get the proportions wrong you end up with a sticky, non-hardening mess that's a huge bother to wipe off and start over. I'm going to wrap a single piece around the tube and I have this theory that each sucessive wrap should be a little narrower than the one below it.
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The idea is that then there won't be an abrupt change in thickness at the edge of the repair. So note how I've modified the shape of the fabric from the original template: it tapers a bit to the left. The right edge is going to be attached to the frame tube first and then wrap around four times, ending with that narrower edge on the left.Edit: note the comment below where it is suggested that this wide-to-narrow wrapping is precisely backwards and that I should have started with the narrow edge first. I believe that's probably the right way to do it.This will turn out to not be strictly necessary — it sands down pretty nicely — but I'd do it this way next time too. Bike upsidedown is not the best position in which to be doing this. Lay the bike on its side, broken side up. The problem is that the epoxy-soaked fabric will want to follow gravity downward.
At least until it starts to set up and gets a bit tacky. But then that only leaves you a couple of minutes where it's still workable.At the time this didn't occur to me, so watch as I do it wrong.(This is the point in the process where you go visit the bathroom, have a little snack, relax for a bit.
When you come back the epoxy's going be prepared and the next hour is time- and attention- critical.). I again mixed up far more epoxy than I needed. The paint brush was used to wet the entire sanded portion of the tube. The fabric was laid out on a disposable surface and a healthy amount of epoxy poured over it.To spread the epoxy over the fabric I needed a roller of some kind. The local horrible Michael's Craft Store seemed like a place to find this roller of some kind.
I've been fooled that way before. What a disasterous place, it's 60% dried flower arranging, 35% scrapbooking (!) supplies, and then an assortment of random art supplies and other garbage. But today I was in luck. One of those random other things was a toy rolling pin for fifty cents.The epoxy is glopped on and then spread out with the roller. You don't need to use a silly toy; a dowel or an empty beer bottle would also work. However, anything you use will never be able to be used for anything else ever again.
So use something disposable.This is also a good time to talk about ventilation. At this point in the process, the epoxy is giving off clouds of god-knows-what kind of volatile poisonous gasses. You should endeavour as much as possible to avoid breathing these vapours. Open windows, a gentle breeze, and a respirator rated for organic solvents are all good friends to have while working.
There are no photographs of the fabric wrapping maneuver because I was pretty busy and covered with epoxy while that was going on. However, it went about exacly as expected after the initial scare where the fabric kept sliding off. You start with one edge of the fabric attached to the frame tube and begin wrapping it, as carefully and neatly as possible. Keep the tension snug, avoid folds and creases, don't let your mind wander.Once the fabric is in place, the next thing is to cover it with another tight wrapping while it cures.
The material of choice for this seems to be black electrical tape wrapped so that the sticky side is out.Something to be careful of here, which I was not, is to wrap the tape in the same direction as the fabric was wrapped. What you're seeing here, though you can't see it, is the tape being wrapped in the opposite direction. This has the misfeature of causing the fabric wrapping to loosen if you're not excessively careful. It eventually came out alright, so maybe not a major issue, but save yourself some worry and do everything in the same direction. Out comes the template again.This time we're putting on the top, outer layer which will be visible for the rest of the life of the bike.
So I have to be careful to get the weave pattern in the fabric to match the direction of the weave pattern in the original fiber of the frame. Carbon fiber fabric seems to come in a large variety of weaves and matching the precise sizes of warp and weft and pattern and texture did not seem easily possible. But we can still come fairly close. And at least match the direction of the weave.So look carefully at the non-damaged part of your bike. Is the weave squarely with the axis of the tube? Or is it at a diagonal?
Try to cut this last piece of fabric out so that the weave will match when wrapped around the tube.(If you don't get this exactly right, it's not a terribly big deal. From more than a couple of feet away, the patterns are invisible to the casual observer.).
I have repaired fiberglass boats which is similar to what you did. Three suggestions I would make is; (1) I was once told to initially fill the inside of the hole with aluminium foil so you have a backing for the epoxy. Another way would be to inset a small piece of cf cloth that is saturated with epoxy into the hole and pull it up to the hole so it acts as a backing which also ensures you have the correct form of the stay being repaired. You can also use the good seat stay as a mold to make the backing from and once the piece has dried you can put epoxy on it and inset it into the hole (there is a wax you can use so backing piece will not stick to the good stay when making it). Hope this makes sense. Just pouring the epoxy into the hole means that the glop inside may break off at some point and rattle inside the tube. And (2) instead of making one sheet of cf cloth with 4 wraps I suggest using 4 individual wraps, each one slightly larger than the previous piece, by about and eighth of an inch along the edge.
Place the smallest one first and then the next larger one, etc. This way you won't have to worry about excess epoxy or loose threads. There are rollers you can buy to make sure the epoxy soaked cf cloth lays flat and any excess epoxy will be squeezed out.
And (3) use acetone to clean up. Also, as a footnote, for boats gelcoat is used which is harder than enamel paint and waterproof. It is harder to to use but you can mix and match different colors to get a match close to the original color. I have a few carbon fiber bikes, so I'm rich with bikes but with money.not so much. Anyway, one bike is a ten year old Specialized Tarmac Comp with a slightly damaged chainstay. Of course with carbon fiber, I keep reading that 'slightly damaged' is only a stone's throw from 'catastrophically damanged', So I'm thinking, if I fix the Tarmac using your experience to guide me, then I can get out and ride it grinnin' - and sell one or more of the other bikes with little regret.
Thinning the herd is a good plan anyway considering that I'm about 70 - but it is definitely fun to pick my ride according to which suits my mood, or is most appropriate for the day. You are so cool for doing this and writing this up so well and with an engaging style. Great work, man! I can't believe you are telling me this! This is instructables not 'purchase-ables'. As I very clearly state in the opening paragraphs here, Trek does NOT 'warranty' anything at all.
Specialized Carbon Frame Cracks
They do have a 'crash replacement' program which means that they will sell me a replacement frame for MORE THAN THE COST OF AN ENTIRE REPLACEMENT BICYCLE! It's basically a scam that they use in their advertising literature in an attempt to fool people who are not good at math. If you'll actually read what I spent the time to write in the introduction, you'll see that I already took that into consideration. And I'm afraid I need to take issue with your unsupported claim that somehow a new frame would be 'safer'. Do you have any evidence that this repair is not 'safe'? Do you have any metrics for quantifying this supposed 'safety'?
Because without them your claim just seems to be coming out of fear: the fear of experimenting, learning new processes, making something on your own. And retreats into passive consumerism. I concur.same thing happened to me.very small minute ding in the seat stay area and TREK 'crash replacement' option was BS!!! They offered me a brand new frame at market value -5%.
I bought a kit off EBay and conducted my own repair. It's a 2013 Domane 4.0 CF. The repair came out awesome and thank you for your write-up!!! Ignore the 'haters'.lol.
I'm not worried about transferring any type of load because one seat stay is stronger than the other. This frame has ISO-flex in the seat post area, so that load gets transferred up stream.
I cannot tell you how much of a Godsend finding this article was! I have discovered an area on my top tube that looks completely like only the clearcoat has sustained some type of crack.
Exactly the same thing happened to my Norco bike. However, while I was getting ready to follow these instructions, to my surprise, the company agreed to give me a new frame (I only paid for moving parts from the old frame to the new one). I just wanted to share some lessons I learned:- keep the derailleur adjusted all the time- keep track of the gear you are at (i.e., don't try to change gear in uphill if you are already at the lowest gear)- regardless of how careful you are, carbon bikes don't last as long as aluminum or steel bikesFinally, thanks to the author for this useful article and thanks to Norco for their great customer service!