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Rebrazing the Downtube to BB

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Rebrazing the Downtube to BB

Old 11-23-10, 04:30 PM
  #26  
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Originally Posted by big_heineken
Danno, the downtube goes all the way in. The tube is rounded(mitered?) to conform with the shell. I'll try to take some pics tomorrow.
No need for pics, I can see the crack clearly in your 1st photo. Interesting that it cracked through both the tubing and lug. Do the two borken ends fit together cleanly like a jagged jigsaw puzzle?

I'm just trying to figure out if the failure was from fatigue or from a more violent impact overcoming the ultimate-strength of the material in that area. Very unusual. Most of the failures I've seen were in the tubing only where it meets the lug. To much lesser degree, I've seen lugs crack just beyond where the tubing ended. But to crack through both, that's very strange...
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Old 11-24-10, 09:21 AM
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Originally Posted by DannoXYZ
No need for pics, I can see the crack clearly in your 1st photo. Interesting that it cracked through both the tubing and lug. Do the two borken ends fit together cleanly like a jagged jigsaw puzzle?

I'm just trying to figure out if the failure was from fatigue or from a more violent impact overcoming the ultimate-strength of the material in that area. Very unusual. Most of the failures I've seen were in the tubing only where it meets the lug. To much lesser degree, I've seen lugs crack just beyond where the tubing ended. But to crack through both, that's very strange...
The tubing didn't crack at all. The first photo is just showing where it cracked, the photo was taken when I first got the bike. The tube came loose and the BB lug cracked on the outside of the cutout. The downtube did not fail, only the brazing did.
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