Repair of a Broken Carbonfiber Bikeframe

Hi, Thanks for looking at my new tutorial. You can watch the full tutorial in the video and have a detailed description in the written step by step part down below. If you like my tutorial, you can do me a favor and subscribe to my youtubechannel for updates and check my other projects too. I’ll post my video’s on instructables to WITH the written detail part if you guys need more explanation. So subscribe to my instructables account as well!
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Most of the materials used can be harmful, resins can be a bit aggressive on the lungs and skin, be sure you work in a proper environment that is well ventilated and clean. Use gloves to work with those resins and a respiration mask. The mask is not only for the smell but as well for the toxic gasses that can access your lungs. The mask is as well good for small dust while sanding. A paper-mask (like the doctors use, is good for the dust but is not good for the gasses coming out of the resin.
That said, lets start the tutorial.

Take some time to see how the part broke and what’s the best approach to repair the part. Here you can see the bike almost completely broke from the down part till upper part of the tube.

Tape everything down that could be scratched or be cosmetically damaged while working on it. That will save you some time at the end.

Remove any loose parts on the broken part. You can do this by using a knife or something sharp to feel where you can remove some loose chips of resin/Carbon fiber. By having a clean and firm part to repair the layers of the repair will have a better bond on the broken part.

Sand the part to be repaired. Remove the topcoat layer (Clearcoat and Resin) to get to the Carbon fiber. Do not only sand the scratch but add some on the left and the right to have a proper bond later on.

Use some cleaning alcohol to remove any dust after sanding.

This is a really important part. Mix some epoxy A+B with some graphite powder. It can be compared to applying bondo on a scratched part but with some resin. This because epoxy resin will have a better bond and should be stronger than bondo. The graphite powder is there to have a better bond on the carbon as well, Carbon and graphite are quit similar.
First mix the Epoxy A+B then add the graphite powder. You should check the technical page of the epoxy you are using for mixing ratios. Once A+B are mixed you add some graphite powder. Add enough to get a more viscous paste you can apply on the part without everything running of.
Note: This isn’t enough as a repair!

Cover the entire crack, use enough and let it fill all the gaps. If it gets a bit to runny, remove some now and then at the bottom. Don’t be afraid it isn’t looking well enough, everything will be sanded once cured, so you only have the gap of the crack filled.

Let the mixture cure overnight and do some sanding to smoothen everything. Start with some 80 grid sandpaper and go till around 200. Do not sand it to smooth because later on the epoxyresin will need some grip on it.

Carbon Fiber
Ive used some Carbon fiber twill weave. First layer is a 200g/sqm followed by 2 layers of 400g/sqm. See how it’s layed down? Direction of the pattern: “/////” followed by “\\\\\\“ this will give extra strenght on torsion and pressure.

Peelply
Peelply is a release cloth. It will make it possible to remove all layers laying on top of this (perforated film, Breeder). It also gives a nice grip if you’d like to add some layers on top of that. Meaning you won’t have to sand it again if you would like to do that.

Perforated film
The perforated film (bleu) Has some tiny holes where the excess resin can pass through.
Note: It is not the resin that gives strength to a part but the fully saturated Carbon fiber cloth making a good matrix with the resin.

Breeder
The breeder is there to take care of a good vacuum all around the part and sucks up excess resin coming through the perforated film and peelply.

Vacuumbag
Sheet of special plastic that does not stick on epoxy.

Wetting out the Carbonfiber
Put you carbonfiber on a sheet of plastic and pour some epoxy resin on it. Squeez it on to Carbonfiber cloth till it is fully saturated. Then remove it from the plastic and wrap it around the part that needs repair. Do this with all the carbon fiber
Vacuumpump
You need a vacuumpump to achieve a good vacuum, causing some pressure on the part and sucking out the excess resin. This pump achieves a vacuum of 99.8%. DO NOT LET THE RESIN ENTER THE PUMP OR YOUR PUMP WILL NOT WORK ANYMORE!
Tacky tape (mouldable high tack tape: yellow)
This can easily be wrapped around the the part at both ends of the repair. Put the vacuumbag on top and ensures full vacuum without any leaks

Once all the materials is put on the part(in right order from bottom till up)
-> Carbon fiber -> Peelply -> Perforated Film -> Breeder -> Vacuumbag with Tacky tape
You can put on the pump. What you’ll see is some small dots of resin passing through the perforated film. This is excess resin of the saturated carbonfiber cloth that is being absorbed by the breeder. Check for leaks, once you have full vacuum let the pump on for 15min than clamp of the hose and shut down the pump. Let it cure overnight now and if you are able to add some heat, do it for a better and faster cure.

Once fully cured you can remove the excess material, do it layer by layer. It should be quite easy to do.

Once all of that is done you can gently sand the carbon fiber to creat a smooth overlap with the rest of the bikeframe

Till now the part is looking dull without any shine (due to the peelply as well).
Mix a new batch of epoxy resin to ‘paint’ on top of it. This will bring the beauty of carbonfiber back.
First clean the repaired part with some acetone or cleaning alcohol to remove any dust of the sanding. Mix a small batch of epoxy and let the bubbles get out of the resin. Give it some time. Small tip: Heat the resin a bit in an oven to make it less viscous and more easy to brush on. Entrapped air will get out more easy as well.

Once the epoxyresin has cured, use some sandpaper again to smoothen everything out again. Go up in grid starting with 120p till 600p. Do not go to smooth or the layer of clearcoat won’t have a good bond on top of it!

Just add several layers. Wait 15min inbetween each layer.

Buff the repair to add some extra shine.

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youtubechannel: http://www.youtube.com/user/matthieutje65
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