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Titanium BB crack repair
#1
Hi all,

I'm new here, but thought I would share my recent experience trying to repair a crack in my Merlin Taiga frame. The crack originated in the weld between the BB and the seat tube during a cycle tour in southern Chile. Two attempts at welding were unsuccessful and it was suggested by several shops that I junk the frame. Having $800+ invested in S&S couplers plus many thousands of miles of love and companionship, I couldn't do it, so I set out to find a repair on my own. My dad is a machinist and we contemplated a mechanical fix - some sort of brace or clamp, but it all seemed too complicated and time consuming. In the end, I went with carbon fiber/resin for ease of application and access to supplies and have just finished the very time consuming process of wrapping and epoxying, sanding and repeating many times. I found some websites of people building bamboo bikes and loosely followed their patterns for wrapping lugs, using 24K carbon fiber tow (basically CF twine, unbraided), wrapping up the down and seat tubes and the chainstays while crisscrossing under and over the bottom bracket. Several layers of resin with snippets of the CF thread followed, with heavy sanding in between each layer. A finish layer of straight resin finished. Below are pix of the final result. Jury is out on how long it'll last, but there's 5 layers of carbon fiber wrapped in various patterns and 7 layers of resin and it is incredibly hard and stiff. The objective was to halt the advance of the crack and stabilize the BB. Let me know your thoughts or if you have any questions.

[attachment=4473]
[attachment=4474]
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#2
A+ for determination, all things considered you did a nice job! hope it works. Thanks for sharing and keep us posted
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
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#3
WOW !!!
Nigel
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#4
Nice repair job, surprised it could not be tig welded, than wrapped if needed.
Did you drill a small hole on both ends of the crack? That usually stops the crack from continuing. That's a great fix used for plexi motorcycle windshields and other applications.
Never Give Up!!!
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#5
Nicely done. You might keep an eye on the tubes where they exit your brace. You may have created a bit of a stress riser in those areas. But hard to believe that joint will give you any more trouble.
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#6
Hey - thanks for the comments. I tried having it TIG welded twice, but at a ratty shop in Santiago, Chile. He didn't have gas and it wasn't terribly clean, but it was the only option at the time. It lasted about 2000k the first time, then just a few hundred the second. The crack is still visible on the seat tube inside the down tube where it meets the BB when the frame is uncoupled, so I can monitor it's progress. I should have drilled the crack before I wrapped, but didn't because I didn't want to drill into the bottom bracket and risk damaging the threads.
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#7
(09-24-2013, 06:45 AM)biciburrito Wrote:  ...... I tried having it TIG welded twice, but at a ratty shop in Santiago, Chile. He didn't have gas ........
without gas it is not TIG... TIG = Tungsten Inert Gas; tungsten electrodes on the electric welder, with the weld area flooded with an inert gas; Argon ideally in air on Planet Earth because it is the same density as air.
Nigel
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