unless you already have a vacuum pump, peel ply, bagging material etc, it's probably cheaper to have it repaired by one of the many carbon repair companies.

That said, do a search on youtube theres some video's out there on carbon fiber construction and I think there's even one of a frame repair that may tell you what you want to know.

I've watched a bunch of those videos and there seems to be a technique that works well that uses electrical tape upside down to create the necessary compression that would be accomplished by the vacuum pump. That's my gameplan so far... None of the videos seem to have good advice on what specific fiber to use. It seems that most use 3K or 6K plain weave and wrap it about 5 times. I'd like to do something akin to what OM or Calfee would do however, not just wing it.

Frame is already sanded down and prepped. Outer layer on downtube seems to have about 11 weaves/inch and the total wall thickness is about 1/16th inch. The chainstay has the same plain weave pattern but closer to the bottom bracket it has layers of 6k and uni. wall thickness there is 5/32nds.

In case anyone thinks I'm getting in over my head here, I built my own house, soup to nuts, including, plumbing and electrical and heating systems, repaired fiberglass boats, I do MIG welding, cabinetmaking, and tractor and automotive repair, so I'm a pretty capable do it yourself-er.

Do you go downhill at speeds in excess of 50mph with only a helmet for protection on any of those devices you have previously repaired?

That's why I made that comment, to ward off comments like yours. I choose the level of risk/reward I am comfortable with, you should do the same. Let those who have something constructive to add offer their suggestions, thanks.

I'm not saying your in over your head, it's just to do it "right" it takes the right equipment, and as I said, at that cost, you can have it repaired.

All of that aside, here's my experiences from doing little CF projects and "repairing" a bike for my friend that he planned on keeping in another state to ride once every few years, so he just wanted it fixed, for cheap, and didn't care how it looked.

I used way more carbon than a professional company would, for the simple fact I wanted it to be strong and he didn't care how it turned out, it was really so I could see how hard frame repairs are in case I ever wanted to do it later on to a nicer bike (I kind of expected to destroy my CF MTB the first year I had it).

From what I know, the professionals cut/sand away or completely remove the damaged sections. How they decide to do one or the other I'm not sure, but if you look at all of the frame repair website photos you will see both methods used. For example my friend (same friend but different frame) had his frame repaired and the company completely cut out his damaged chain stay, then replaced it with a good chainstay from another damaged frame that was identical. I've seen others where they cut out all of the cracked material then sand it down so the patch will blend in. I'd guess you don't have sections to replace with a new frame so you'll have to do the cut away method. You don't want any sharp corners or square edges in your cuts, you'll want the cut to be oval/round shaped and you need to make sure you get all of the cracked/damaged area or the crack can spread out.

Depending on how much you cut away, you may need a core material or the carbon will collapse into the frame. You could shoot some spray foam into it, then sand it down to the shape of the frame. It won't add much weight but may absorb some resin which could add a little weight, but then this is a DIY job so I doubt your too worried about that.

Lay it up. I have no good advice here, just speculation. I overkilled the seat tube and wrapped the whole thing. he wanted it strong not pretty, but if I were to do it over, and had to repair a chain stay I'd probably put a layer of uni in 4 different directions in as many plys as they used then 1 top ply of 3 or 6k (whatever matches the original). A down tube wouldn't need as much (as you mentioned), and probably woudn't need 4 directions either, 2 is likely the norm, but I'm guessing here.

Also theres a video that shows you how to build up your own "pre-preg". Its essentially all your CF sandwiched between two sheets of over head projector plastic, so you can spread the resin evenly between them all, then you cut that out using a razor and you have the exact shape you want, in the layup you want with the resin already applies. Only problem would be having that lay evenly on the frame, so maybe do a few layers out a time getting bigger with each layup so once it's all sanded it blends in better.

Now, electrical tape works, but it's not the same as vacuum bagging. It doesn't get as tight, as even, and you will definitely be sanding ridges out of the top carbon layer when you are through.

If you need a good source for resin and CF I'd go to Soller Composites, and also call and talk to the owner, he's very knowledgable and will probably be a lot more help. http://www.solarcomposites.com

If you have any other questions feel free to send me a PM.

Thanks, I have been looking at sollercomposites site. That's where I thought I would purchase the material from. The damage is just surface cracking, the frame is not severed at all, so I wasn't planning on cutting out sections of the frame. The only reason I know the thickness of the two areas is because I drilled 1/8" holes in the site of the cracks to try to determine the thickness of the layup in those locations. I don't care either what the frame looks like when I'm done, I just want to be back to riding sooner than the 6 to 8 weeks it seems like it would take to get it professionally repaired a Calfee's. I also want to save the money, and it's nearly impossible to find a frame large enough to fit me. And I want to be able to actually compete soon! I just ordered a few books on composite fabrication and repair so I will know quite a bit more soon, but my plan as of now is to just do additional wraps over the sites of the cracks.

I love to design and build new tools/gadgets all the time for my work, so investing in the vacuum pump and some new skills will be a better investment in the long run that just sending it away for repair at $600+ (since there are two spots to repair).

Admittedly this guy seems to be winging it to an extent, but what do you (more knowledgeable folks) think of his method? http://www.instructables.com/...ycle-Frame/?ALLSTEPS

Up front disclaimer: this is all based on knowledge of repair of fiberglass/CF boats, so take what you will.
Lots of resin on a boat is a bad thing because resin burns...I don't suspect you're as concerned about lighting your bike on fire, so you're probably good there. I can tell you that vacuum bagged stuff tends to look nicer.
The most important thing to remember is that you're going to get all your strength from the adhesive quality of the repair; that is, every test I've ever seen done on a repair, both tension and flexural, it always fails at the repair seem. You can get damn close with good technique, but you can't make the actual fibers link together from one to the other.

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IG: idking90

A vacuum pump is not necessary for the repair and won't do you much good in this case. In order to get a vacuum bag to work, you would have to place the whole frame inside a bag and you would struggle to keep things straight and true as bag vacuum increased and you would risk collapsing the actual frame tubes.

The electrical tape method previously recommended works great. A more elegant solution, albeit more time consuming, is to create sheath of 0.010" mylar which goes over the repair and then use a heat activated shrink tape over the mylar to create consolidation pressure. This will create a molded look over the repair and only need finishing at the ends and a minimal amount at the mylar seam depending on how careful you are in creating the sheath. Don't forget to wax the mylar so that you can remove it after the resin has cured.

There are lots of sources out there. I've used CST (http://www.cstsales.com) for more than 15 years now with good success. The MGS resin system they provide is a bit higher quality product than the ProSet or West Systems resins generally used for hobby type wet layups.

When you prep your layup, remember to taper the plies out so that you don't create a stress riser at the end of the repair. To be conservative I would recommend a taper of 2" either side of the cracks.

I would also recommend experimenting with a scrap piece of tubing prior to attempting the real repairs as once you do the repair, it is a whole lot of work to re-repair your repair.

Thomas

Not quite, load transfers from ply to ply at a seam or repair via shear force in the matrix (the resin in this case). As long as their is sufficient overlap from ply to ply to not exceed the shear capability of the matrix, there is no difference in ultimate strength. Most failures at repairs occur due to shear failure in the matrix which then propagates into a larger failure. Be conservative in your overlap distance and you can avoid these issues

Thomas

This is cool. This thread needs pics.

. I'm sorry but this is not true at all. You can bag just the repair, and there is no way you are going to draw enough pressure to collapse a section of frame.

Not trying to be mean or insensitive, but can I be the beneficiary on your life insurance?

 
The electrical tape method previously recommended works great. A more elegant solution, albeit more time consuming, is to create sheath of 0.010" mylar which goes over the repair and then use a heat activated shrink tape over the mylar to create consolidation pressure. This will create a molded look over the repair and only need finishing at the ends and a minimal amount at the mylar seam depending on how careful you are in creating the sheath. Don't forget to wax the mylar so that you can remove it after the resin has cured.

There are lots of sources out there. I've used CST (http://www.cstsales.com) for more than 15 years now with good success. The MGS resin system they provide is a bit higher quality product than the ProSet or West Systems resins generally used for hobby type wet layups.

When you prep your layup, remember to taper the plies out so that you don't create a stress riser at the end of the repair. To be conservative I would recommend a taper of 2" either side of the cracks.

I would also recommend experimenting with a scrap piece of tubing prior to attempting the real repairs as once you do the repair, it is a whole lot of work to re-repair your repair.

Thomas[/quote]
Thanks for the source, it seems to be the best one so far, and there's a good bit of instruction on that site. As for the taper I have enough room to go 3" in either direction on the chain stay and about 2" toward the bottom bracket on the downtube, so I have the room you recommend and I was planning on using it all. How many plies do you recommend and how much difference in length should each one have? For example should the first ply be 4" long and the next one 4 1/4", and the next one 4 1/2" etc, or should the first one be 1" wide, next one 2" wide, next 3" etc. Or should I do what the chap on the example I posted do and use one piece and wrap in continuously in one application and have it taper out as it wraps. I know there is probably no one right or wrong way to accomplish this but the recommendation of an experienced person would be helpful. I will definitely do a scrap practice repair.

There is a video of someone doing this type of repair with a vacuum pump http://www.youtube.com/watch?v=s25hVcjjH5Q His patch is just two plies of the same length, so maybe that's the best way to go? He does use Uni-directional and then 6k bidirectional which seems like the way manufacturers probably do it.

Old thread - but how did this work out - how many layers did you apply. About to commence a chainstay repair - I have done top tube before but not a chainstay. From some of the comments above I can clarify (in my view some things)


1. Vacum vs tape (electrical or Shrink) depends on the shape. I have three carbon frames - all have indents in the shape that make tapping ineffective. If something is perfectly round then a tape may work.


2. Layers - If I am doing 2 layers in the same direction it is with 1 piece of fibre wrapped twice. If the crack is only on one side I overlapp for the duration of the crack


3. More fibre is not necessarily better - making it too strong can make other areas a weak point - it really just needs to as close to original - these things are designed to flex

Fixxed several frames with three/four layers in different directions weave and tape compression. They are all fine including seatstays on a cx bike. I have also made several parts with a similar techniques. Go for it my friend. good videos on youtube.

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