Carbon-repair process of my TFSA (SL6 clone) frame

[TidyDinosaur]

So I crashed my 1 month old TFSA frame 2 weeks ago. In the process I hit a metal pole with the horizontal part of the non drive chainstay... This caused my frame to crack in this spot. I also cracked my collarbone, but that's healing nicely after some surgery...

I asked for a quote for the repair and the cheapest I got was 250 € without paint (I asked for this since I can just cover it up with some black plastic protection foil)...
Since the frame is about 450€, I decided to just get another frame instead of having it repaired...

I like DIY and I like working on bikes so I have also decided to try the repair myself and keep the bike for the smart trainer. I am not confident enough in my carbon repair knowledge (=none) to ride the bike outside after the repair.

So this is what it looked after the crash:


So I ordered all the supplies to do the repair myself and watched a lot of youtube... The supplies were 130€ but I got too much of everything (including 1m² of 200g/m² 3k carbon sheet) and it included some stuff I will not need to use so that could be a lot lower...

This afternoon I went for the first step: sanding it down. I used a Dremel and just some 150 grit sanding paper for sanding by hand.

During sanding it became obvious that the cracks are rather big so just sanding away some patches here and there was not going to work. I decided to sand the whole area where the cracks were so it would be easier to cut and apply the new carbon patches.

If the weather is OK I will apply the new carbon patches and epoxy tomorrow. I was thinking to start with a big square patch that covers almost the entire sanded area, than a second patch that is about 1cm smaller and than end with 1 big square to cover the 2 previous and hopefully leave a nice finish... I have shrink tape to wrap the spot afterwards and hopefully squeeze out the excess epoxy.

This is where I stand now:

[Wet Noodle]

I've heard that the textbook way was to make the sanding area smaller and smaller (towards the crack) as you go deeper into the laminate. Each layer should be exposed ~2 cm wide or something like that. Then just build up laminate the opposite way, starting with smaller pieces and getting larger by each layer (think tetris). Ideally, you'd want something like a "layered scarf joint" between the old and the new laminate (I hope that makes sense).

Just something I picked up from people who seemed actually knowledgeable on the topic (as opposed to me). I have no background in composites and might have got it wrong.

[TidyDinosaur]

I've heard that the textbook way was to make the sanding area smaller and smaller (towards the crack) as you go deeper into the laminate. Each layer should be exposed ~2 cm wide or something like that. Then just build up laminate the opposite way, starting with smaller pieces and getting larger by each layer (think tetris). Ideally, you'd want something like a "layered scarf joint" between the old and the new laminate (I hope that makes sense).

Just something I picked up from people who seemed actually knowledgeable on the topic. I have no background in composites and might have got it wrong.

And you can also find experts that say you have to start with the largest piece of carbon and build up with smaller and smaller pieces...

The problem is that there are multiple cracks in the location I'm working on. And they also run in different directions... That's why I decided to just sand away a lot... In some area's there is almost no carbon left...
I'm just going to use this frame inside so it's not that critical...

[TidyDinosaur]

This morning I continued the process. I had cut 3 patches yesterday but they were not big enough when I tried them on the tube so I had to redo it... I decided to not use 3 separate patches because it would be difficult with the seams since I would have to wrap each patch around the tube. I went for one long piece or carbon that tapers from one end to the other and that I can wrap around the tube 3 times.



I started with the smallest end and wrapped it around the tube. Afterwards I wrapped it with shrink tape to compress everything. Now it will have to harden until tomorrow... I don't think it will win any beauty prices, but it looks nice and sturdy after a few hours of hardening...

[Sebastian]

Are you using pre preg sheets or dry cloth and apply the resin+hardener afterwards?

[TidyDinosaur]

Dry cloth, but I read a tip somewhere that you could stick some parchment paper with spray on adhesive to the carbon sheet to keep it from fraying when cutting. This worked very well.
I applied the epoxy to the carbon sheet before I stuck it to the frame.
I first applied some epoxy to the frame to cover the entire area, than wrapped the soaked patch around the tube and covered it with some more epoxy. After that I wrapped with the shrink tape and heated the tape.

[jonathanf2]

As much as carbon gets a bad rap for being more prone to breaking in certain instances, it's cool you can actually patch carbon up. Maybe after this, you should try fixing your MTB bottom bracket as well! 

[TidyDinosaur]

As much as carbon gets a bad rap for being more prone to breaking in certain instances, it's cool you can actually patch carbon up. Maybe after this, you should try fixing your MTB bottom bracket as well! 

Yeah, after this repair, the crack in the BB of my MTB seems easy

[TidyDinosaur]

This morning I removed the tape and protective plastic to see the result. It is not very aesthetically pleasing but that is just because I will be leaving it like this and will not be sanding and painting...
Structurally it looks very solid. The sound when tapping on the tube sounds exactly the same on the repair than it does on the rest of the tube and there is no flex. I think I actually would be OK to use this frame as my outdoor frame if I would not have ordered a new one already...

Things I could have done better:

• Put the electrical tape to mask off the area further away from the repair area. Now the tape acted like a sort of barrier/dam for the epoxy and this created an abrupt height difference between the epoxy and the existing surface. Easy enough to solve if I would sand and paint this area though...
• Use less epoxy for the final coating. Now the epoxy has seeped under the electrical tape and there is some epoxy on the "good" side of the tape. Again this would be absolutely no problem when sanding...
• Put some small strips of carbon on the lowest area's of the repair before the final carbon patch. Now there is a slight indentation where I sanded away the most carbon.

[Sebastian]

Well done! I applaud your DIY attitude!
I repaired my VB218 frame as well and found it much easier than I thought once I’d done the necessary research. I used masking tape to stop the carbon cloth from fraying. Worked well enough.
I too read that the recommended technique is to build up the daläget area starting with small patches and work your way towards bigger patches. Basically to fill the void that you created when sanding away at the crack.
If it was my frame, I’d probably sand the area and put a bit of clear coat on it to observe it and once I’d be sure that it holds I’d paint over it.

[bxcc]

Awesome for saving the frame. For future repairs, here's a few unsolicited tips.

1) You mentioned this already but do multiple layers. In this instance, you'd want to start with maybe a strip that is 1 inch wide and do one wrap with a bit of overlap. Second strip should be roughly 2 inches wide and the overlap of this layer should not sit on top of the overlap of the first layer. Keep the strips growing in width until you have plenty of coverage over the entire repair. This makes the cracked area have the most layers for strength and each additional layer helps transfer the loads to the good material.

2) If using a weave, change the direction of the weave between layers. Carbon weave is strongest in certain directions so alternating the layup can help even out the stresses put on the repair.

3) Always make sure the carbon weave is fully saturated with epoxy before laying it on the frame unless you are going to vacuum bag the repair. If not, you could end up with some dry spots in the carbon repair. A good portion of the strength comes from the epoxy so it's critical that you have proper saturation.

4) Before cutting your sheets to the size you need, leave them a bit big and lay them flat inside a plastic bag, I like to use plastic zip-loc bags but if you have to do larger pieces, any plastic can work. Pour a bit of epoxy on the carbon and close up the bag with little to no air in it. Use a squeegee to force the epoxy into the carbon fabric. This will make it "pre-preg" carbon fabric. Before removing the carbon, layout the size of the piece you need with a marker on the bag and cut it out with scissors. When you're ready to do the layup, you can carefully remove the two pieces of plastic off of your cut piece.

5) If you ever read an article from an expert that says to start with large patches and go smaller with each layer, you should REALLY question there credentials.

Either way, great job and this should work perfectly for an indoor bike.

 

[TidyDinosaur]

Thanks for the tip.

I put the bike back together again this afternoon, and now I kind of regret ordering a new frame...   

[Serge_K]

Very nicely done, and thank you for sharing your process.
A big advantage of these chinese frames is that if you crash it, you have 500 eur at risk, not 5000. It's the sort of thing that helps sleep better at night.
Good luck with your recovery. Collarbones seem to break like matches.

[TidyDinosaur]

Very nicely done, and thank you for sharing your process.
A big advantage of these chinese frames is that if you crash it, you have 500 eur at risk, not 5000. It's the sort of thing that helps sleep better at night.
Good luck with your recovery. Collarbones seem to break like matches.

Thank you. Recovery is going great. I never expected it to go so fast. After 2 days I did not need the sling anymore and on the fourth day I was riding indoor (with my sling) at a low wattage for 45 min. We are now 2 weeks further and stitches are removed so I have been doing some heavier work (still indoor) since a couple of days... Checkup with the doctor on the 14th and after that I hope I can start riding outside again.

The bike is holding up fine. A bit of a shame to just use it indoors, but it is what it is... The new Hygge frame should arrive in the next few weeks so than I can build me a new bike for the road.