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PostPosted: Fri Nov 14, 2014 9:52 pm 
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Joined: Sun Dec 19, 2010 4:24 am
Posts: 173
Location: Ann Arbor, Michigan
Someone ran over this rear wheel in a crash-- still only a couple of millimeters out of true, and it can hold my weight (180 lbs sprinter), but wondering if it would be possible to repair this to race-able condition? Would be for a lighter rider, around 120 lbs and a climber. I have lots of carbon experience with making stuff from scratch, but I'm only familiar with wet layups and not necessarily with patching stuff.

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My general plan so far:
First step would be to unlace the rim to de-tension it, and sand down the outer layer to bare carbon.
Secondly, try to "bump out" the collapsed portion and sand that like crazy. My idea was to use the spoke holes to put something in there, like a latex bladder, to inflate outwards to give positive pressure. (alternatively, I could just block all of them off except for one and then use the rim as its own bladder!)
I'd then wrap with 3-4 layers of 3k, with a final asthetic layer of uni to finish it off. Sand, clearcoat, decals.

What do you guys think? any advice? Any comments on the feasibility of the above proposed procedures?

Thanks!

Stefano


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Posted: Fri Nov 14, 2014 9:52 pm 


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PostPosted: Sun Nov 16, 2014 4:04 pm 
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Joined: Fri Feb 10, 2012 4:27 pm
Posts: 352
How much is your time worth?
That is a pretty major crack and honestly probably not worth the time. Even if you did manage to do all that you'd still have a very major line of weakness where the crack occured and you'll be risking fatige failure over time. My guess is that you probably have fiber damage or fraying extending beyond the crack. Proper carbon repair is done by cutting out the entire affected section properly. and I dont know how well that section is going to hold tension from the spoke. The wheel is not going to be balanced.

All in all if youre going to race on a potentially dangerous and sub par rim why race at all.


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PostPosted: Sun Nov 16, 2014 11:08 pm 
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Joined: Sat Dec 13, 2003 2:25 am
Posts: 4516
Location: Canada
Forget your time, what about your head?! If you are proposing to race on it, it is tantamount to negligence to knowingly line-up with substandard equipment. If you want to risk yourself whilst training, I guess that is your look-out, but to risk others is unconcsionable.


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PostPosted: Mon Nov 17, 2014 4:46 pm 
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Joined: Sun Dec 19, 2010 4:24 am
Posts: 173
Location: Ann Arbor, Michigan
Thanks for your responses guys. I would obviously never want to put anyone in danger, I definitely think that this particular rim repair is well within my abilities to repair though. it's not on the brake track, spoke hole is fine, and there are no other damaged parts anywhere on the rim.

I think I might modify my procedure a bit though.. To prevent the crack from propagating, I will cut out the affected segment, make a fiberglass mould of the rim profile off of another part of the rim, then use 4-6 total layers in compression mould.

I'll post pics when done!


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PostPosted: Thu Nov 20, 2014 12:29 pm 
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Joined: Fri Feb 10, 2012 4:27 pm
Posts: 352
still think it's a dumb idea.

you might have CF skills, but How are you going to manage the alu/carbon brake interface? do you have the proper epoxy to glue that together? is this epoxy going to remain unaffected by elevated temperatures at the brake track at high pressures? that carbon segment is not a fairing like HED jets, that is a structural segment. it is going to be taking load, and quite abit of it. if you're going to vut out entire alumnium rim segment, either you've got an aluminium extrusion die at home with plenty of time, or... its a dumb idea.


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