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Old 03-12-07, 11:27 PM   #1
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Why cant carbon fiber be repaired?

As a autobody tech for over 30 years I have repaired just about every thing from corvettes to personal water craft and with the latest in 2 part adhesives like duramix or Lord fussor,I am sure there must a way to do it. Questions I have are ;What resin is used and where can I get the fiber mat.
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Old 03-13-07, 06:22 AM   #2
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You're asking the wrong questions.

The question should be:

Why should I never, under any circumstances attempt to repair any form of stressbearing monocoque manufactured in inherently damage-intolerant materials that exhibit catastrophic failure modes rather than replace the component in tis entirety?

Carbon frames are entirely stress-bearing. There is no point, just like aluminium alloy or steel or titanium or pasta, that does not suffer significant loading at all times in use. An auto body panel is a cosmetic component, they are very different things to compare the performance and requirements of. I'm somewhat concerned at the idea of boats having smashed bits of their hulls repaired, but they too are much less loaded per unit sectional area than a bike frame.

I really do not recommend repairing a carbon frame by chopping out damaged portions and sticking a new bit in, or even overlaying a new prepeg on the top of a crack and hoping it holds. You are aware that even the most thermally stable resins degrade with repeated heating? Brittle fibre-reinforced matrix composites are not intended to be repairable. They are intended to be scrapped when they fail.

That said, if you feel the need to do this, you'll have to speak to the manufacturer of the frame. There isn't one resin used in CF frames, there are a host.
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Old 03-13-07, 06:25 AM   #3
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Calfee Design does carbon repair.
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Old 03-13-07, 06:59 AM   #4
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yes u can repair it... in a matter of fact isnt that hard to repair... just like with steel put something in the interior, glueit really well... then wrap over the top with more carbon... sand it, paint it... done...

Air force usually repair carbon in planes, In chile i know 2 guys that have been repairing treck carbon frames and a couple of looks track bikes... As long as u get the tubes straight before wrapping the crack with fiber u are pretty much done.

I'm not saying that the carbon bike will get better than new but at least it can be repaired, and u can use the bike at least probably for one more season. The aluminum can be repaired also but the AL cured process makes it too expensive to even try, u know... u need to get the whole bike in a furnace and stuff to get the welded part and the rest of the bike with the same properties, thing that is expensive to try in a used frame... dont worth it

UM
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Old 03-13-07, 06:59 AM   #5
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Nooooooooooooooooooooo!!!!! [/Darth Vader]

Hehe
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Old 03-13-07, 07:12 AM   #6
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Originally Posted by ultraman6970
yes u can repair it... in a matter of fact isnt that hard to repair... just like with steel put something in the interior, glueit really well... then wrap over the top with more carbon... sand it, paint it... done...
Just because it isn't hard doesn't mean it's worth doing. Not quite sure what you're saying with the steel repair analogy. Never seen a patch-up on a smashed steel tube before.

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Originally Posted by ultraman6970
Air force usually repair carbon in planes, In chile i know 2 guys that have been repairing treck carbon frames and a couple of looks track bikes... As long as u get the tubes straight before wrapping the crack with fiber u are pretty much done.
The CF skins of planes are substantially different from a bike frame. They are not one piece skins, not even on the F22 or the JSF. As I said, they aren't pure, stress bearing monocoques. They simply fix the panel, and that panel is bolted to the airframe. Last time I checked, bike frames didn't have any superstructure inside the tubes or monocoque. Second, they're not even all CF. Not all reinforcing fibre-matrix combinations are so unforgiving. Why do you think a kevlar layer lies under the CF/BF skin of F1 racecars? Third, the matrix is usually now bismaleimide, which is not available for bike frame manufacturers, as far as I am aware. Some of the tougher matricies are even now not available.
Does Trek recommend that these guys do what they do?

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Originally Posted by ultraman6970
I'm not saying that the carbon bike will get better than new but at least it can be repaired, and u can use the bike at least probably for one more season. The aluminum can be repaired also but the AL cured process makes it too expensive to even try, u know... u need to get the whole bike in a furnace and stuff to get the welded part and the rest of the bike with the same properties, thing that is expensive to try in a used frame... dont worth it
You're right. It won't be better than new. It won't even come close to old. As for the bit about re-solution and age for aluminium frames that are re-welded, are you seriously recommending using uncured resin to hold this 'patch' on, or do you recommend cold-cures? Because I can't think of anyone with a materials degree tht would agree with you on that one. You have to stove cure the CF resin too....


I'm not trying to be arsey here. I'm a materials engineer who's seen waaaay too many people injured by ****ty processes and really bad ideas that seemed good at the time. Repairing CF bike frames, contrary to what you've seen or been told is not a good idea.
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Old 03-13-07, 06:57 PM   #7
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Oh come on that's too severe! This whole question is so broad he could be talking about a boat, we have no idea that its a load bearing or heavily loaded component of the structure, it could be some section that got hit my a car where glue and tissue paper would get the job done.

There is no problem fixing carbon, the problem is that carbon is rarely used in the kinds of stuctures that are going to give a lot of original style pleasure to those who fix them. But take something like a high performance trimaran that is hugely loaded compared to a bike. Take some daring do type who flips it in a race, he gets hauled off by a helicopter, maybe it get proinged by a few boats that try to salvage it, finally floats past the Azores, they grab it, dry it our and clean it up and bond on a nice workmanlike repair with some WEST system, re-fit it and weekened race it or use it for charters. No problem at all.

Actually a more comon example is when they decide to try to break a record in the around the world races, and cut in new bows and sterns, and then go crashing around the globe at 20 knots, on a patched together boat. Sure the orginal parts where made in a full length mold in a heated autoclave, but I'm doubtful on all the nose jobs, not to mention secondary bonds.

You would have to get lucky with the kind of fracture you are trying to fix if you have much hope of returning it to near new condition, but for a happy second life, there could be lots of possible fixes.

Fiber mat? Do you mean like mat fiber glass? Again as mentioned if it's just a light weight fairing that's one thing, but if it's load bearing in a big way, you need to use something with continuous fibers to spread the load. Mats build heavy bulk fast, protect underlying fibers from scratches, add stiffness is a rather heavy way.
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Old 03-13-07, 08:59 PM   #8
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ok
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Old 03-14-07, 12:01 AM   #9
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Quote:
Originally Posted by Peterpan1
Oh come on that's too severe! This whole question is so broad he could be talking about a boat, we have no idea that its a load bearing or heavily loaded component of the structure, it could be some section that got hit my a car where glue and tissue paper would get the job done.
Again, cosmetic over structural.... Name a CF bike part that isn't loaded and wouldn't cause you an injury if it went suddenly.

Quote:
Originally Posted by Peterpan1
There is no problem fixing carbon, the problem is that carbon is rarely used in the kinds of stuctures that are going to give a lot of original style pleasure to those who fix them. But take something like a high performance trimaran that is hugely loaded compared to a bike. Take some daring do type who flips it in a race, he gets hauled off by a helicopter, maybe it get proinged by a few boats that try to salvage it, finally floats past the Azores, they grab it, dry it our and clean it up and bond on a nice workmanlike repair with some WEST system, re-fit it and weekened race it or use it for charters. No problem at all.
Then that tub should never see the water again. End of. And as for the components of a performance Trimaran? They tend to be much more blended and radiused than bike frames. And whole hell of a lot thicker. You'll notice I used the words 'per unit sectional area'. Then of course if they come apart in the middle of a race, you've still got a life jacket on.

Quote:
Originally Posted by Peterpan1
Actually a more comon example is when they decide to try to break a record in the around the world races, and cut in new bows and sterns, and then go crashing around the globe at 20 knots, on a patched together boat. Sure the orginal parts where made in a full length mold in a heated autoclave, but I'm doubtful on all the nose jobs, not to mention secondary bonds.

You would have to get lucky with the kind of fracture you are trying to fix if you have much hope of returning it to near new condition, but for a happy second life, there could be lots of possible fixes.

Fiber mat? Do you mean like mat fiber glass? Again as mentioned if it's just a light weight fairing that's one thing, but if it's load bearing in a big way, you need to use something with continuous fibers to spread the load. Mats build heavy bulk fast, protect underlying fibers from scratches, add stiffness is a rather heavy way.
No, I mean proper prepeg 90 degree sheet.
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Old 03-21-07, 05:29 PM   #10
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"Again, cosmetic over structural.... Name a CF bike part that isn't loaded and wouldn't cause you an injury if it went suddenly."

I'm sure with your background you have seen plenty of finite element program outputs where the various parts come out colour coded for loading. Very simplistically in a monocoque CF frame the parts where the tubes would be are high load and the others aren't. CF likes to propagate a small flaw into a big ripper, but I wouldn't have any problem with a flaw in the "non-tube" areas being fixed. If you have a damage in the hot areas, where the tubes would be in a non-mono design, the only difference in repairing it is the amount of material required. No way it is going back to original condition.

What is an example of a structure with a huge structural hole in it? What about a canoe? the whole top is missing and the loads are taken off by some sheet metal screws and a few sticks of wood, or could be alloy in the case of carbon, more industrial looking. What about a Kayak where the cockpit is a secondary bonded flange? Those things see both tension and compression, say when surfing. I would agree those aren't always heavily loaded.

Hey carbon can be an easy material to misjudge. Ever see that America's Cup boat they got wrong where the whole bow came off under forestay pressure? Even the experts make mistakes, and they even make them with new stuff let alone repairs.

"Then that tub should never see the water again. End of."

Yeah well that's the difference between the US and the rest of even the first world, we just aren't throwing any carbon out.

"And as for the components of a performance Trimaran? They tend to be much more blended and radiused than bike frames."

Right bikes just don't care about aero components... You know all those jagged lines on carbon wheels.

"And whole hell of a lot thicker. You'll notice I used the words 'per unit sectional area'. Then of course if they come apart in the middle of a race, you've still got a life jacket on."

Right probably in the middle of the south ocean. A beam folds and the rig comes down, no bell egg crate is going to save your head from those weights. I hear you about sectional area, but the reality is both groups are building structures to break. There was one bad race a few years back when a lot of the fleet blew up. Many boat just went "bang". They build them light for inshore racing which is most of the year, and then they also run them out in the big weather, well this was the perfect storm... I think it was '02 RDR

http://archives.cnn.com/2002/WORLD/s.../rhum.capsize/

"No, I mean proper prepeg 90 degree sheet."

I'm sure you do. I was wondering what the OP was talking about, I should have been clearer.
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Old 04-12-07, 02:31 PM   #11
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Quote:
Originally Posted by Peterpan1
"Again, cosmetic over structural.... Name a CF bike part that isn't loaded and wouldn't cause you an injury if it went suddenly."

I'm sure with your background you have seen plenty of finite element program outputs where the various parts come out colour coded for loading. Very simplistically in a monocoque CF frame the parts where the tubes would be are high load and the others aren't. CF likes to propagate a small flaw into a big ripper, but I wouldn't have any problem with a flaw in the "non-tube" areas being fixed. If you have a damage in the hot areas, where the tubes would be in a non-mono design, the only difference in repairing it is the amount of material required. No way it is going back to original condition.

What is an example of a structure with a huge structural hole in it? What about a canoe? the whole top is missing and the loads are taken off by some sheet metal screws and a few sticks of wood, or could be alloy in the case of carbon, more industrial looking. What about a Kayak where the cockpit is a secondary bonded flange? Those things see both tension and compression, say when surfing. I would agree those aren't always heavily loaded.

Hey carbon can be an easy material to misjudge. Ever see that America's Cup boat they got wrong where the whole bow came off under forestay pressure? Even the experts make mistakes, and they even make them with new stuff let alone repairs.

"Then that tub should never see the water again. End of."

Yeah well that's the difference between the US and the rest of even the first world, we just aren't throwing any carbon out.

"And as for the components of a performance Trimaran? They tend to be much more blended and radiused than bike frames."

Right bikes just don't care about aero components... You know all those jagged lines on carbon wheels.

"And whole hell of a lot thicker. You'll notice I used the words 'per unit sectional area'. Then of course if they come apart in the middle of a race, you've still got a life jacket on."

Right probably in the middle of the south ocean. A beam folds and the rig comes down, no bell egg crate is going to save your head from those weights. I hear you about sectional area, but the reality is both groups are building structures to break. There was one bad race a few years back when a lot of the fleet blew up. Many boat just went "bang". They build them light for inshore racing which is most of the year, and then they also run them out in the big weather, well this was the perfect storm... I think it was '02 RDR

http://archives.cnn.com/2002/WORLD/s.../rhum.capsize/

"No, I mean proper prepeg 90 degree sheet."

I'm sure you do. I was wondering what the OP was talking about, I should have been clearer.

HUH???
As a "practical mechanical engineer" = not only designs but builds, and who also knows a thing or 2 about CF, metals (ferrous and non-ferrous) and ceramics, I have to fully agree with Falanx.

There are no non-bearing tubes that make up a bike frame. Im afraid EVERY tube in a bike frame is structural... even the BB tube. Thats just the way it is. Plus I have over 20 years experience in road bikes... damn, now you made me feel old!
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Old 04-12-07, 03:00 PM   #12
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Well, it can be done, but it's never gonna be as strong or as optimized as the original structure. You'll be adding a tonne of material ON TOP of the original tubing in order to transfer loads across the broken ends of the original fibres. Think of it as a thick band-aid on top of the tubing. Very unsightly and gainly not to mention heavy.
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Old 04-13-07, 12:34 AM   #13
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"There are no non-bearing tubes that make up a bike frame. Im afraid EVERY tube in a bike frame is structural... even the BB tube. Thats just the way it is.

Sure, but they are differently loaded, and some are more severely loaded than others. That's not the main point of the section, which is harder to refute, and consists of the fact that in the absence of specific instance we don't know how severely compromised the frame is and what options might be available to fix it.

So your telling me...: if you were on the cycling equivalent of a desert island, the only possible escape is to ride away. you are provided with a state of the art carbon framed bike with one fairly severe flaw that renders it not currently useable, and all the carbon fiber epoxy etc... you could want, but only for repair. But you are stuck there for ever and ever? That's pretty much my picture of an engineer also!

A bad habit to get into is when you really know something, and it provides reasons for why something can't be done, to get too attached to those reasons notwithstanding the fact a lot of people are making work the very thing you are claiming is impossible. Hey you've signed on for the idea that all these sailing yachts that are being chopped and diced, just can't be happening.

Didn't Falanx tell me you can't harden mild steel? (I think they did that on Myth Busters the other day I recognized the frantic shriek in the quench). It's like meeting Doctor No.

"Well, it can be done, but it's never gonna be as strong or as optimized as the original structure. You'll be adding a tonne of material ON TOP of the original tubing in order to transfer loads across the broken ends of the original fibres. Think of it as a thick band-aid on top of the tubing. Very unsightly and gainly not to mention heavy."

Your right about optimized, but it can probably be as strong. There are lots of places you could add the material to without having to have it on the outside. In most cases the weight penalty is not going to be that great. A lot of these monocoque structures are made out of clamshells joined together along seams, the structures aren't always as pure as they seem.
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Old 04-13-07, 09:15 AM   #14
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Okay, I was gonna leave this thread alone, seeing as it seems whenever I answer a question on any subject, you feel the need to attempt to score points off my comments, demonstrating your understanding isn't as sound as you'd like to believe, and it's not becoming. I let your other reply go because you just can't reason with some people, but...

You want to make this a flame, by all means.


Quote:
Originally Posted by Peterpan1
So your telling me...: if you were on the cycling equivalent of a desert island, the only possible escape is to ride away. you are provided with a state of the art carbon framed bike with one fairly severe flaw that renders it not currently useable, and all the carbon fiber epoxy etc... you could want, but only for repair. But you are stuck there for ever and ever? That's pretty much my picture of an engineer also!
That kind of attitude it pretty much what I was getting at. I can't decide if that's a flippant strawman or just puerility.

Quote:
Originally Posted by Peterpan1
A bad habit to get into is when you really know something, and it provides reasons for why something can't be done, to get too attached to those reasons notwithstanding the fact a lot of people are making work the very thing you are claiming is impossible. Hey you've signed on for the idea that all these sailing yachts that are being chopped and diced, just can't be happening.
I, nor anyone else claimed anything was impossible. You seem to confuse risk with possibility.

Quote:
Originally Posted by Peterpan1
Didn't Falanx tell me you can't harden mild steel? (I think they did that on Myth Busters the other day I recognized the frantic shriek in the quench). It's like meeting Doctor No.
A quench shriek doesn't mean *anything* was hardened. You seem to be confusing cavitation with the bain strain transformation. You also seem to be confusing MythBusters with real science.

Quote:
Originally Posted by Peterpan1
"Well, it can be done, but it's never gonna be as strong or as optimized as the original structure. You'll be adding a tonne of material ON TOP of the original tubing in order to transfer loads across the broken ends of the original fibres. Think of it as a thick band-aid on top of the tubing. Very unsightly and gainly not to mention heavy."

Your right about optimized, but it can probably be as strong. There are lots of places you could add the material to without having to have it on the outside. In most cases the weight penalty is not going to be that great. A lot of these monocoque structures are made out of clamshells joined together along seams, the structures aren't always as pure as they seem.
Nope, you're right. The weight penalty isn't going to be great. But I wasn't talking about weight. I was talking about repeated restoving of fibre-reinforced polymer composites undergoing thermal degradation of thermosetting or thermoplastic epoxy matricies, but hey, if you want to ignore what I was saying to construct your own strawman, be my guest. It wouldn't be the first time.
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Old 04-14-07, 02:15 AM   #15
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Quote:
Originally Posted by Peterpan1
Your right about optimized, but it can probably be as strong. There are lots of places you could add the material to without having to have it on the outside. In most cases the weight penalty is not going to be that great. A lot of these monocoque structures are made out of clamshells joined together along seams, the structures aren't always as pure as they seem.
Yeah, I think the repair is kinda like a broken-bone, it may actually be stronger than the original depending upon how much stuff you lay up. I've repaired snapped golf-clubs and fishing-poles before and they ended up just fine. You have to blend the repair and taper it into the original tubing to be very smooth so as to not cause a stress-riser.

Here's a picture of Damon Rinard's 1st CF frame (it snapped the top-tube):


And a picture of his repaired top-tube. The transition between the old & new frame is actually 1/2 way in the middle of the down-tube:
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Old 04-16-07, 12:14 AM   #16
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I wanna see a Damon Rinard vs Jobst Brandt Celebrity Deathmatch. Because no matter who wins, we all win.
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Old 05-05-07, 08:36 PM   #17
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- Here is an interesting manual on repairing carbon fiber military aircraft. It's mostly about setting up a program for same. Around page ten they get down to describing some techniques, like a negative mold to slap on a patch.... Awesome, how do they manage it.

- "That kind of attitude it pretty much what I was getting at. I can't decide if that's a flippant strawman or just puerility."

See that's where you can easily get yourself into trouble: Try words you understand the meaning of next time.

- "I, nor anyone else claimed anything was impossible. You seem to confuse risk with possibility."

You got me there, your words were "Why should I never, under any circumstances attempt to repair any form..." You're right, you didn't say it was impossible. Jump on it, the Navy needs to know.

- "A quench shriek doesn't mean *anything* was hardened."

True, but if a guy is hardening something one can tell the sound superquench makes because it is quite distinctive.

"You seem to be confusing cavitation with the bain strain transformation. You also seem to be confusing MythBusters with real science."

Snore. If you actually do the work you learn a lot of sounds, etc... that are quite informative. We know it works because we have done it. And by now, for the cost of some soaps you probably have around the house, a pieces of mild steel, and a torch you could have proved or disproved it yourself.

- "I was talking about repeated restoring of fibre-reinforced polymer composites undergoing thermal degradation of thermosetting or thermoplastic epoxy matricies, but hey, if you want to ignore what I was saying to construct your own strawman, be my guest. It wouldn't be the first time."

I'm sure you were!
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Old 05-09-07, 10:01 AM   #18
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Calfee specializes in CF repair: http://www.calfeedesign.com/howtosendrepair.htm

From their webpage: "We can repair damage to most any brand of carbon fiber frame. From minor chain suck to frames broken in half. We can even make a flexy frame stiffer. The repair job is usually hard to notice and people are surprised at how good they look. We don't repair problems with frames that are a result of bad design. This includes most aluminum-to-carbon bonding. We do not repair carbon handlebars or forks."

There you go, a well known bicycle builder specializing in CF who also repairs CF from any brand. Doesn't get better than that.
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Old 05-10-07, 12:16 AM   #19
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Iam sorry this question caused so mutch controversy. however I was able to get a broken frame frome a Lbs to try my repair idea .The frame had a broken bottum tube actually broken in half with a large mashed area on the bottum .I cleaned up the edges .I then made an aluminum sleve to match the inside diameter of the tube making it 6inches long to give a 3inch overlap in the repair area.I prept the area inside and out by sanding useing 80grit and 3m adhesion promoter. I coated the sleave and inserted it into the tube then used used cf mat and resin and let it set next day I sanded primed and painted a graffic over the repair area. Itook it back to my Lbs and they are going to test it this weekend.I will let you guys know how it holds up.
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Old 05-10-07, 12:24 AM   #20
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hey Mommy,why can't I have a pony ?
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Old 05-10-07, 12:48 AM   #21
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jeez what is with you guys.
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Old 05-10-07, 01:33 AM   #22
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now if you're careful, you can do a really good CF repair job by unpicking the carbon fibres from the matrix, unweaving back about three inches either side of the damaged area, and then reweaving using a stronger gauge carbon fibre. lay the threads down in the original orientation, making sure you have plaited the new threads inot the old weave at least 2.5 inches back. then reimpregnate with resin, insert your bladder inside the tube, pump up and get the shape right, then re coat the outside and bake. simple. just like darning socks.

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Old 05-10-07, 01:41 AM   #23
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Quote:
Originally Posted by Pac-Mule
jeez what is with you guys.
Ignore the knuckleheads.

I'm interested to hear how this turns out and what the LBS says. Thanks for posting.
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Old 05-11-07, 03:25 PM   #24
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Quote:
Originally Posted by urodacus
now if you're careful, you can do a really good CF repair job by unpicking the carbon fibres from the matrix, unweaving back about three inches either side of the damaged area, and then reweaving using a stronger gauge carbon fibre. lay the threads down in the original orientation, making sure you have plaited the new threads inot the old weave at least 2.5 inches back. then reimpregnate with resin, insert your bladder inside the tube, pump up and get the shape right, then re coat the outside and bake. simple. just like darning socks.
Dude, it would only need to be this complicated if you wanted the original strength AND weight. We've already admitted that in order to get sufficient strength to cleanly transmit load across the repaired joint, there's going to be a weight-penalty.

Quote:
Originally Posted by Pac-Mule
Iam sorry this question caused so mutch controversy. however I was able to get a broken frame frome a Lbs to try my repair idea .The frame had a broken bottum tube actually broken in half with a large mashed area on the bottum .I cleaned up the edges .I then made an aluminum sleve to match the inside diameter of the tube making it 6inches long to give a 3inch overlap in the repair area.I prept the area inside and out by sanding useing 80grit and 3m adhesion promoter. I coated the sleave and inserted it into the tube then used used cf mat and resin and let it set next day I sanded primed and painted a graffic over the repair area. Itook it back to my Lbs and they are going to test it this weekend.I will let you guys know how it holds up.
This sounds interesting. I think it'd definitely work, but how well depends upon some variables. Got a couple questions:
  1. How thick was the aluminium sleeve you inserted in the down-tube?
  2. What kind of clearance/interference-fit did you have between the sleeve and the outer CF tube?
  3. What of glue did you use?
  4. How many layers of CF did you lay up on top?
Due to the nature of tubing, I suspect that it's really going to be the outer CF layer that takes most of the stress.
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Old 05-11-07, 09:07 PM   #25
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Ah, Danno, I was , urm, how can I say this? Kidding?


Sorry you missed it...
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