Guest 000 Posted August 14, 2017 Share Posted August 14, 2017 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. Quote Link to post Share on other sites
erice 732 Posted August 14, 2017 Share Posted August 14, 2017 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 Quote Link to post Share on other sites
Guest 000 Posted August 14, 2017 Share Posted August 14, 2017 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? Quote Link to post Share on other sites
Guest 000 Posted August 14, 2017 Share Posted August 14, 2017 Thank-you all. That's tomorrow's project sorted. And thanks form the lady biker as well. Quote Link to post Share on other sites
erice 732 Posted August 14, 2017 Share Posted August 14, 2017 oh CSM chopped strand mat? would have thought horrible stuff for the forces involved imho ideally carbon tow, wound round lots of tow or uni, laid perpendicular to crack with more tow or biaxial (or biaxial cut weave) over the top Quote Link to post Share on other sites
Guest 000 Posted August 14, 2017 Share Posted August 14, 2017 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. Quote Link to post Share on other sites
Frank 157 Posted August 14, 2017 Share Posted August 14, 2017 yep,, carbon tow, lash n bind, then epoxy kevlar tow probably OK also. If you prime with epoxy that may prevent the electrochemical corrosion mentioned. Quote Link to post Share on other sites
Ed 143 Posted August 14, 2017 Share Posted August 14, 2017 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. Quote Link to post Share on other sites
cj! 19 Posted August 14, 2017 Share Posted August 14, 2017 Like Ed said, sand with Wet and Dry and use epoxy instead of water. Look at Bamboo bike building for some wrapping inspiration around the BB. Quote Link to post Share on other sites
erice 732 Posted August 15, 2017 Share Posted August 15, 2017 carbon wraps on bamboo bikes Quote Link to post Share on other sites
Guest 000 Posted August 17, 2017 Share Posted August 17, 2017 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. Quote Link to post Share on other sites
erice 732 Posted August 17, 2017 Share Posted August 17, 2017 looks brilliant! not going to edge it with rope like your similarly beautiful dinghy? Quote Link to post Share on other sites
Guest 000 Posted August 18, 2017 Share Posted August 18, 2017 [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. Quote Link to post Share on other sites
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