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IMG_20170812_100206.jpg

 

This bit is the front end of the wife's recumbent trike. The pedal crank goes through the the horizontal tube with the black ends. The vertical bit with the crack in it (courtesy of Emirates Airlines) only holds the front derailleur so is not structural, but the weld holding the crank tube on is. If I weld up the crack then the heat affected zone is going to impact on this weld and being subject to high stresses, it will fail. During manufacture these bits are heat treated after welding to avoid this but 7000 grade alu cant be treated twice. A new assembly would be nice but not available.

So, if I cleaned off the paint, abraded and degreased the alloy and brushed on an epoxy coat immediately before any oxidation could get going, and then encapsulated the entire end in multiple layers of CSM and resin, would this work?

Any alternative ideas/solutions welcome. The Keeper of the Purse can't go cycling and she's getting a bit twitchy.

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i tossed some carbon weave on the work bench

 

forgetting there was an old bike wheel there

 

all nice and dry, only light contact

 

but the corrosion on the alloy rim caused by the carbon was like i had painted on battery acid...only drier

 

so you won't get away with wrapping carbon on alloy without bad electrolysis starting almost immediately

 

BUT 

 

if you make your first layer on the alloy glass, and then keep the carbon on the glass

 

you should be able to do something like a caffee, if not as pretty

 

8cfec76bcb71759f0da90d2e7a08d9f3--carbon

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Wow! Just as well you wrote that because was thinking about carbon fibre. I guess what I'm trying to do is replicate in GRP something like the old lugged bicycle frame joints, and what I need to know is will epoxy adhere to aluminium without and special prepping. And will it be strong enough?

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oh CSM

 

chopped strand mat?

 

chopped-strand-mat-250x250.jpg

 

would have thought horrible stuff for the forces involved

 

imho

 

ideally carbon tow,

 

Carbon_Tow_on_Bicycle_large.jpg?v=143693

 

Carbon-TOW_grande.png?v=1436931774

 

wound round lots of tow or uni,

 

uni01.jpg

 

laid perpendicular to crack 

 

with more tow

 

gallery_1988_55_170349.jpg

 

or biaxial

 

cx016-carbon-multiaxial-biaxial-+-45-400(or biaxial cut weave) over the top 

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I have epoxy resin, some CSM, some 10oz cloth and a lot of double bias tape, but no carbon fibre. That's too exotic to be found in Whangamata, so have to make do with what's to hand. The cracked vertical pole is not a structural party of the frame and almost no loading on it.

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Bonding epoxy to aluminum can be problematic due to how fast the alu oxidises. One way around this is to paint the alu with epoxy, then sand the alu while the epoxy is still wet. Keeps the oxygen off of the active surface and makes a good bond.

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This is the finished repair.

I had never heard of tow before, but a quick internet search revealed it to be long single strands of carbon loosely bundled together. Taking Erice's advice about carbon on alloy, decided to make something similar out of 10oz fibreglass cloth. So the Keeper of the Purse was given the job of painfully unravelling about 2m of cloth and making strings of about 50 strands each. She didn't care for the job much but hey, it's her bike that's broken, right?

The strands bound up quite nicely and only needed a tiny lick of epoxy filler to finish it off. It seems to be plenty strong enough.IMG_20170817_194226.jpg

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[quote name="Knot Me... maybe" post="189917" timestamp="1503015810"

 

I hope it serves your boss well ;)

 

I suppose she's pleased with it. I put her trike together this morning, told her to take it for a test ride and I haven't seen her since.

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