Repairing Cracked Carbon Frame

[DJ84]

Hi All,

 

I have a frame that has a crack on the top tube about 7cm long.

I want to try fix it and build it up and see if this 29er thing works for me.

 

Who has any guidance as to how I can fix this.

Would be a fun project as I want to clean the frame and repaint as well.

 

Sanded down to the crack as you can see.

[Jokerman923]

I would suggest to get in touch with the guys who custom paint bicycle frames as they have the know how on this.......

 

Cycle Art is one of them

 

Alternatively you can look for other companies at the back of local cycling magazines

[Li Mu Bai]

Get hold of Andy (0827860940) or Steve (0824626860) at Maccabi Racing - they do great work with carbon and carbon repairs.

[DJ84]

I would like to try do it myself as a project.

So advice on how to fix as well as where to buy some carbon.

 

I am on the westrand in Gauteng if that helps.

[BogusOne]

Have you got the material to do the repair yet?

[NotSoBigBen]

Google

 

http://www.instructables.com/id/Repairing-a-Carbon-Fiber-Bicycle-Frame/

[BogusOne]

1st you will have to "clean" up a bigger area to work with. Don't have enough time now to give you the whole spread on how to do the repair as im at work but its nothing complicated nor difficult. Easier than working with normal fibre glass.

 

Anyhow will send you a PM later on the steps and also where to buy your materials if you are interested.

 

Nice project

[DJ84]

1st you will have to "clean" up a bigger area to work with. Don't have enough time now to give you the whole spread on how to do the repair as im at work but its nothing complicated nor difficult. Easier than working with normal fibre glass.

 

Anyhow will send you a PM later on the steps and also where to buy your materials if you are interested.

 

Nice project

 

Thanks BogusOne,

seen your build and its impressive.

 

Just want to have a bit of fun and if it doesn't work I will send it to someone to get fixed.

 

Look forward to your PM

[DJ84]

Google

 

http://www.instructa...-Bicycle-Frame/

 

Thanks NotSoBigBen,

Will have a read when I get a chance.

[4u2nv]

just put two hose clamps around it.. good as new :ph34r:

Edited July 3, 2013 by 4u2nv

[stratus5]

Thanks BogusOne,

seen your build and its impressive.

 

Just want to have a bit of fun and if it doesn't work I will send it to someone to get fixed.

 

Look forward to your PM

 

Hi,

 

It should be fairly easy to repair. I actually dont think its structurally compromised at the moment. Some frames are built as two halves and then "joined" together. It has possibly cracked down that join where the two halves meet, but there is normally a layer or two of carbon tape under that join (under the crack) to give it strength.

 

Since its painted, there is no need to make it pretty ;>)

 

1. Get a dremel or similar with a the sanding wheel that is about 1cm in diameter.

2. Put some tape down each side of the crack about 5mm each side of the crack and parallel to the crack as a guidline.

3. WIth the dremel at about 25000 rpm, carefully sand out the crack so that you have a shallow hollow about 2mm deep and 10mm wide along the entire length of the crack.

4. Try not to breathe the carbon dust. Its not good for the lungs.

5. Put new tape (preferbly insulation tape) along the edge of the sanded area and all around the underneath of the frame as you dont want spill over from the repair to stick to the frame. Its a bugger to sand hardened epoxy ;>)

 

You need some good epoxy and carbon fibre. Ampreg 21 with a standard hardener would be good, which you can get from AMT http://www.amtcomposites.co.za/ They have an office in Jhb.

Its difficult to source very fine weave (ligter than 200gsm) carbon fibre. The best you can get is probably 200 GSM standard plain weave. AMT stock it.

I dont think you can buy less than 1m, but once you can repair one frame, you can get others cheaply and repair;>)

 

6. The mixed resin has about 1 hour of usable pot life, so there is no need to rush once mixed.

7. Cut a few strips (5?) of carbon cloth about 2cm wide. You can use masking tape stuck to the carbon cloth to make cutting it easier, or else the ends fray and run horribly whilst you are trying to cut and position it. Leave about 2mm of masking tape on the cloth to keep the ends in place.

 

8. Time to get messy. Get some gloves. Latex will do, but its not best for epoxy. AMT has the right gloves.

9. Wet out the strips of carbon weave with epoxy. Its easiest to do this on a plastic sheet. the sort of plastic you used to cover school books with works well.

10. Paint some epoxy in the raw sanded area on the bike.

11. Lay the strips of carbon weave along the sanded crack one by one, starting with the widest strip and getting narrower if you want to minimise the sanding required once the epoxy has set

12. Make sure you build up enough carbon layers, such that it is now higher than the top of the sanded out area.

 

The sticky carbon mess now needs some pressure added for the best result.If you could find a piece of flexible plastic longer than the repair and about 3cm wide (1mm or 2mm ABS), or a plastic tube that matches the curve of the frame, that would be great.

 

13. Place the plastic on top of the repair and use insulation (must be insulation) tape to fix it in place. Wrap loads and loads of tape around the repair with as much tension in the tape as you can manage, without snapping it.

14. The pressure will now cause all excess epoxy to piss out everywhere and drip all over the place, hence the tape on the frame all around the repair, and a cover on the lower part of the frame that might get dripped on

15. Wait at least 12 hours and then unwrap your present.

16. Depending on how well you have done the layers and there overlap, you may need to do major or minimal sanding.

17 Sand sand sand with sandpaper (80 grit) attached to a sanding block so that you dont sand hollows, until the tape along the edges of repair starts to show. Then change down to 220 grit wet or dry paper and as you get closer and closer to the original surface, go through the grades until you get to about 600 grit.

18. That should be it. All you have to do now is fill any minor blemishes with auto filler (grey paste) and paint.

 

Hope that helps.

 

Edited July 3, 2013 by stratus5

[LRW]

stratus pretty much nailed it......

 

take note of the cutting process for carbon cloth though (its a nightmare actually.......ive never tried the masking tape trick, will remember that in future).

 

Ive worked with that yellow/black carbon/kevlar cloth to make a few car bits.......and cutting that stuff is just as nasty

[stratus5]

stratus pretty much nailed it......

 

take note of the cutting process for carbon cloth though (its a nightmare actually.......ive never tried the masking tape trick, will remember that in future).

 

Ive worked with that yellow/black carbon/kevlar cloth to make a few car bits.......and cutting that stuff is just as nasty

 

You can also use a spray on adhesive. 3M makes one. AMT will have it. Spray some adhesive on a thin plastic sheet. Stick the carbon to the plastic. Cut the shape you want. After you have put the carbon where you want it and tacked it down with some epoxy. Peel off the plastic.

Edited July 3, 2013 by stratus5

[DJ84]

Thanks NotSoBigBen,

Will have a read when I get a chance.

 

That was actually quite informative.

He filled the chainstay though with epoxy,

I wonder if that would be possible with the Top Tube as it is a fair size to fill.

[DJ84]

You can also use a spray on adhesive. 3M makes one. AMT will have it. Spray some adhesive on a thin plastic sheet. Stick the carbon to the plastic. Cut the shape you want. After you have put the carbon where you want it and tacked it down with some epoxy. Peel off the plastic.

 

Thanks Stratus,

That is very helpful.

So you don't think that I need the carbon to wrap around the frame at all?

 

Really looking forward to doing this.

[stratus5]

Thanks Stratus,

That is very helpful.

So you don't think that I need the carbon to wrap around the frame at all?

 

Really looking forward to doing this.

 

Definitely dont wrap the carbon all around the frame. The fillet type repair that I mention above is similar to a metal weld. Very good way of fixing a crack and very strong if done properly.

 

Again, I think that crack is purely cosmetic, where the two faces of the half mold process join, but repair as above just to be sure.