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Old 12-29-10, 02:49 PM   #1
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Stop drill cracked carbon?

Does anybody here have experience with this? I've got a crack in one of my carbon seatstays and I'm contemplating sending it off to Calfee for repair. I think I've got the general idea of what they do: Sand to bare carbon, apply resin, apply carbon wrap, apply more resin, pressure wrap the repair, sand and paint to taste. There is no mention that I can find anywhere of what is done to treat the crack itself and stop it from continuing to crack. Any insite to this or is halting the propogation of the crack left to the resins, carbon wrap and pressure?
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Old 12-29-10, 03:10 PM   #2
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I am not an expert in carbon fiber properties but from what I can tell cracks do not propagate in composite materials the same manner they do in metals. I suspect that stop drilling a crack in a composite frame may not be sufficient to prevent it from propagating.
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Old 12-29-10, 04:46 PM   #3
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you might also try ruckus components: http://www.ruckuscomponents.com/
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Old 12-29-10, 04:59 PM   #4
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Old 12-29-10, 08:02 PM   #5
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Cool video, not what I expected.
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Old 12-30-10, 09:15 AM   #6
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Ok, I've had a little more time to watch this video. Is that what is normally done in the repair of a bicycle tube? The part he was working on has some type of honeycomb behind it that had to be replaced first therefore he had to cut the old section out and bond in the new one. I don't think my bike has that issue? For a simple crack, do they actually cut out the bad part? The rest of it I mostly understand, templating and laying up the layers of carbon over the replaced section. However, what is the last layer called the 'peel ply'?

I guess I had imagined it was more like this:
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Old 12-30-10, 11:19 AM   #7
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Here's what I would recommend you do - send it in for repair.

Or someone with experience who does a lot of carbon fiber. Unless you have much more composite work experience then you let on.
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Old 12-30-10, 12:02 PM   #8
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I had no intention of doing it myself.. I was just trying to understand what I would be paying for.
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Old 12-30-10, 01:01 PM   #9
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The repair that Calfree will do will be far more in line with what you saw in the Carbon Mods pole repair. The vid that AEO linked to is more in line with what would be done to repair a ding in an F-22 or a current fancy carbon sailplane or one of the America's Cup yachts.

As for what you should do in prep for shipping it off I'd suggest you limit your work to stripping off the parts so you're shipping less weight and don't do anything else. No stop holes or any other prep work. Leave that to Calfree or whoever will be doing the repair.
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Old 12-30-10, 02:31 PM   #10
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Thanks for the info, I thought it would be more like the second but I suppose, depending on the severity they may need to cut out the bad part, form up behind it and start over.

Again.. I won't be doing any of this myself, other than stripping, shipping and reassembling.
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Old 12-31-10, 02:14 AM   #11
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I repaired a large crack in the seatstay of my carbon Madone using a similar kit to the one shown in the Carbon Mods video above. I used a kit from carbonology.com to re-wrap the entire length of the seat-stay (from brake bridge to dropout) even though the damage was limited to an area less than 5 cm in length. I've now used the bike for another year with no noticeable affect on performance. The procedure was very similar to the Carbon Mods video shown above, except more layers of carbon were provided with different directions of weave, each of which needs to be applied, shrink wrapped, and left to dry before the next one is applied. You have to be pretty confident to decide to do it yourself, but none of the steps are very difficult, and the end result is good.

I was never certain about the cause of the damage to my seat-stay. It most likley happened while being stored in a hotel's garage, where it may have been dropped or hit by someone/something, but I can't be sure. I didn't discover the damage for about one week because it was on the underside of the seat-stay, so it was difficult to see. I had ridden the bike once or twice (depending on when the damage occurred) during that time without knowing about the damage and without noticing any difference in the feel of the bike, so I felt that it was structurally OK, and just needed to be beefed up with the carbon repair kit. The damage on mine was not a simple crack, so there was no consideration of whether to drill it first, but I also saw no mention of doing so in my research. I think you are correct that the extra carbon applied with the repair is meant to take care of the original crack, and there is no way that it could propogate after that is applied.

If you want to pay to get it done professionally, then I'm sure their results will make it almost as good as new. However, similar results can be achieved by doing it yourself.

Last edited by Chris_W; 12-31-10 at 02:18 AM.
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Old 12-31-10, 03:10 AM   #12
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Great video ... the carbon fiber repair process is not rocket science
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I guess I had imagined it was more like this:

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Old 12-31-10, 03:26 AM   #13
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I wonder if that heat shrink tape works comparably to vacuum bagging. It seems like it might be good enough for fishing poles but perhaps not good enough for bike frames. Just guessing, though.
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Old 12-31-10, 09:02 AM   #14
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Originally Posted by Chris_W View Post
I repaired a large crack in the seatstay of my carbon Madone using a similar kit to the one shown in the Carbon Mods video above. I used a kit from carbonology.com to re-wrap the entire length of the seat-stay (from brake bridge to dropout) even though the damage was limited to an area less than 5 cm in length. I've now used the bike for another year with no noticeable affect on performance. The procedure was very similar to the Carbon Mods video shown above, except more layers of carbon were provided with different directions of weave, each of which needs to be applied, shrink wrapped, and left to dry before the next one is applied. You have to be pretty confident to decide to do it yourself, but none of the steps are very difficult, and the end result is good.

I was never certain about the cause of the damage to my seat-stay. It most likley happened while being stored in a hotel's garage, where it may have been dropped or hit by someone/something, but I can't be sure. I didn't discover the damage for about one week because it was on the underside of the seat-stay, so it was difficult to see. I had ridden the bike once or twice (depending on when the damage occurred) during that time without knowing about the damage and without noticing any difference in the feel of the bike, so I felt that it was structurally OK, and just needed to be beefed up with the carbon repair kit. The damage on mine was not a simple crack, so there was no consideration of whether to drill it first, but I also saw no mention of doing so in my research. I think you are correct that the extra carbon applied with the repair is meant to take care of the original crack, and there is no way that it could propogate after that is applied.

If you want to pay to get it done professionally, then I'm sure their results will make it almost as good as new. However, similar results can be achieved by doing it yourself.
Why didn't you take advantage of Trek's replacement policy?
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Old 01-02-11, 03:13 AM   #15
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I wonder if that heat shrink tape works comparably to vacuum bagging. It seems like it might be good enough for fishing poles but perhaps not good enough for bike frames. Just guessing, though.
Similar shrink tape came in the tube repair kit I used from carbonology. It is certainly intended to be used for bike frames because the product description states "Broken a bike frame? ... this is the kit you need." The tape does the job of compressing the carbon together while the glue dries, it shrinks quite a lot and puts significant pressure on the tube, I don't think you need anything more than that. I overlapped the tape quite a bit more than what is shown in that video to make sure that every part was well covered. I didn't have a hot air gun, but the combination of a hair dryer and kitchen oven seemed to do the trick well enough.
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Old 01-02-11, 04:43 AM   #16
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Racerone, I'm a boat builder, retired now, and have worked plenty with carbon/epoxy laminates including racing yachts and aerospace projects. With thicker laminates, the repair area is ground down and tapered so that the built up area is no thicker than the original. On a thin walled bike frame, tapering may not be possible to any significant degree. Most likely the patch would consist of a number of plies wrapped around the area and very carefully sanded to blend in with the original. You may be able to repair it yourself but a pro job would probably be invisible.
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Old 01-02-11, 11:07 PM   #17
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Here are a few pictures of said crack. I just got the bike back from the bike shop, after all is said and done, Trek won't warranty, not a surprise. They want me to ship it to them, and for only $200 they'll look at it to see if it can be repaired. If not they'll cut a big chunk out of it and send it back. Shop says, mark the crack, ride it, watch for it to get worse. If it does, then action might be needed.

I'll take door #2.


Quick overview of where it is, you really can't see it in this picture, but it's right there in the middle.


It doesn't actually look this bad, I oversharpened this photo and jacked up the contrast.



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Old 01-03-11, 03:41 AM   #18
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...cracks do not propagate in composite materials the same manner they do in metals.
+1
Drilling a hole CAN stop a fatigue crack from growing in metal, but what' you've got is something else on both counts.
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Old 01-03-11, 04:00 AM   #19
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... The part he was working on has some type of honeycomb behind it that had to be replaced first therefore he had to cut the old section out and bond in the new one.
An important part of the characteristics in bicycle tubing is that it's tubular. If you have a section that's so mangled that it's no longer round(ish) it'd lose strength even if the wall material as such was still OK. In that case there are two parts to the repair:
1) recreate shape
2) recreate wall integrity

For someone who has round stock available, cutting out and replacing can certainly be the simplest and most elegant option. Of course it also depends on how long the damaged section is.
If I had a (fairly) short section that was badly squished, but still stable enough to retain its shape I'd probably just wrap over it.

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...what is the last layer called the 'peel ply'?
Basically, it's a ply (layer) that is peeled off after curing. It's used to control the surface texture of the finished product. If you're doing a boat deck you might use a fairly coarse peel ply to create a non-slip surface. If you're doing something that is to be painted later you might use a finer one, to leave just a little bit of texture to help the paint adhere.
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Old 01-03-11, 08:51 AM   #20
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they repair a frame rather than replace it? that seems odd.
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Old 01-03-11, 10:19 AM   #21
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they repair a frame rather than replace it? that seems odd.
I've never heard of them actually repairing one, though I have seen what happens when they say they can't.
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Old 01-03-11, 12:53 PM   #22
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I doubt that Trek would repair a frame since what came back would LOOK repaired. And that is not their way.

However if warranty from Trek is not an option then a good servicable repair is certainly possible by an outfit that knows their stuff.

The crack in your pictures is really small and fine. I'm wondering if this is actually a crack in the carbon or could it be just a spot of the paint has delaminated from the carbon below and cracked due to flexing of the stays when riding. A lot of times the finish does not have the same or greater flexibility as the material under it and when that happens the paint itself can delaminate from the carbon. So unless you can press on the tube around the crack in such a way that you can feel the round shape distorting and the levels on each side of the crack moving it is quite possible that this is just a paint crack.

The way to find out is to get a small knife in there and see if you can chip away the paint from the carbon. This is something that needs to be done in any event either to allow proper inspection of the carbon and to make any subsequent repairs. So it's not like you're ruining anything by doing this yourself. And it may turn a big repair job into just a paint touch up.

The idea would be to genty but firmly try to chip and lift away the paint at the crack. If it only chips in small bits instead of bigger flakes then it is still firmly bonded and it becomes more likely that the carbon itself has cracked. But if it comes away in BB size or larger flakes then it's a good indication that the paint itself has lost its adhesion. But don't stop until you've got the entire spot bared of at least the top color so you can check the carbon for cracks. And of course it is up to you if you think you want to try this or leave it for the shop that would be doing the rest of the work.
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Old 01-05-11, 12:11 PM   #23
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I'm no carbon expert but that does not look like a crack to me.

If your lucky,the seat stay may be open to the seat tube or there may be a drain hole in the tube.If so,blow compressed air in the hole,squirt soapy water on the crack,look for bubbles.

You'll know FOR SURE if it's a crack or not and you don't have to screw up the paint.

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Old 01-05-11, 08:03 PM   #24
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Photos can be very weird. But it doesn't "look" like a crack, more like the paint has a scratch. But again photos can be weird. Have you had an LBS look at?
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Old 01-06-11, 09:47 AM   #25
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I'm no carbon expert but that does not look like a crack to me.

If your lucky,the seat stay may be open to the seat tube or there may be a drain hole in the tube.If so,blow compressed air in the hole,squirt soapy water on the crack,look for bubbles.

You'll know FOR SURE if it's a crack or not and you don't have to screw up the paint.
Nope, it's sealed up tight as far as I can see.
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