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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 07-16-11, 03:24 PM   #1
qqy
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How bad is this seatpost crack and what can be done? (Columbus Thermachrom steel)



Overtightend the seatpost collar and did this to my favorite bike in the world. Since it's not load bearing, I was hoping there's a reasonable fix to this. It's been surprisingly difficult to get a local store or framebuilder to give me a quote or suggestion on what to do. I rode it for a bit after doing this unknowingly and it hasn't gotten much worse.

So far, the range of options is: braze in a lug (most extreme) to bead weld it to hold the crack. Looks like the seatpost is a bit too small, so maybe weld in a shim?

Any help is greatly appreciated...
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Old 07-16-11, 04:19 PM   #2
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find someone with a internal hole gauge to try to figure out what the right seatpost size is and get one that size. It does make sense that the undersized seat post caused the problem. Unfortunately, with a crack that big it might not stop growing. In fact, my thought is that it ends at the white dot that is almost all the way to the weld. I think you could braze half of a tube as an overlay on top of this, but it would be hard to make it look right.
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Old 07-16-11, 04:50 PM   #3
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Thanks for the reply. Sounds like the 'braze in a lug' may be the best option.. ugh..
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Old 07-16-11, 05:52 PM   #4
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If it were mine, I'd just braze on a 1" wide 1mm thick reinforcing strip of 4130 formed around the rear half of the seat tube centered vertically over the crack, then redrill the hole and cut the slot in the reinforcement.
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Old 07-16-11, 07:37 PM   #5
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That's actually exactly what I want. I've seen this before with this very frame and the solution was to braze a diamond-shaped patch over the back of the tube and recut the notch.

Very good solution. I think this is what I will ask for, and if it fails, then resort to a lug. Thanks to both suggestions above - this gives me a bit more confidence that this can be resolved reasonably.
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Old 07-16-11, 11:23 PM   #6
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actually, scooper just expressed himself more clearly -- that's what I meant. However, you do need to get a seatpost that is the right size or this will fail
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Old 07-25-11, 10:53 PM   #7
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I would think that drilling a hole at the end of the crack would help keep it from spreading. Then possibly brazing the crack and filling the hole with silver or brass to finish it off.
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Old 07-25-11, 11:27 PM   #8
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do you have any experience with repairs like that?
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Old 07-26-11, 12:45 AM   #9
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I have a MTB made from TT OX2 tubing that had a similar crack develop shortly after I purchased the frame. I brazed a 2" long sleeve into the top of the seattube and used a smaller seatpost to fit the sleeve ID. Except for the seatpost diameter, the repair is nearly undetectable and I have been riding it that way for nearly 20 years.
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Old 07-26-11, 06:42 PM   #10
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No; but I my understanding is that the hole at the bottom of the seatpost cut was there to prevent stress risers from occurring. Of course, the crack still occurred, so maybe I'm missing something. The brazing of the crack and filling the hole would be purely cosmetic.
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Old 07-26-11, 10:48 PM   #11
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No; but I my understanding is that the hole at the bottom of the seatpost cut was there to prevent stress risers from occurring. Of course, the crack still occurred, so maybe I'm missing something. The brazing of the crack and filling the hole would be purely cosmetic.
I might get flamed for this, but I see this kind of thing so often I'm gonna say it anyway- If you have no experience with this type of repair, why would you reply in a thread about making said repair?
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Old 08-03-11, 10:53 PM   #12
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School learning verses actual experience in steel crack repair. Drilling a hole to stop a crack was discussed in a materials class in college, roughly 20 years ago.
Some googleing brought up a couple results on the subject:
in airplanes - http://www.mechanicsupport.com/metal_fatigue_crack.html
in highway signs - http://www.ce.udel.edu/cibe/news%20a...hop/Dexter.pdf
about halfway through there is a formula for determining the size for a stop-hole diameter - rule of thumb is listed as diameter should be 1/3 the length of the crack - not good news for bike repairs.
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Old 08-04-11, 07:24 AM   #13
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I do have a technical question, why the cut notch is so long??
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Old 08-04-11, 09:41 AM   #14
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School learning verses actual experience in steel crack repair. Drilling a hole to stop a crack was discussed in a materials class in college, roughly 20 years ago.
the thing is, you need to keep the crack tip from opening. If the crack tip doesn't open, there is no advantage to drilling a hole, the crack still isn't going to move. Stop drilling alone will not stop a crack. It removes the crack tip and should delay the formations of new cracks for some short period of time. I went through extensive training in the subject of fixing damaged aircraft and I don't remember the subject of stop drilling ever coming up at all. That's because it does nearly nothing. The crack in the OP is possibly somewhat different because it is apparently mode III crack. But it is long enough that it might propagate in mode I. The bottom line is that it needs reinforcement back at the slot.
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Old 08-04-11, 06:40 PM   #15
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I had something similar to this decades ago and it was fixed with a TIG welder in just a few minutes. Ugly as hell, but never failed.
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Old 08-19-11, 02:24 PM   #16
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Is there enough seat tube above the top tube to slot the front after putting the diamond shape patch on?
I repaired a mountiain bike with a similar problem but sleeving the entire seat tube mitered to tuck into the top tube with the diamond extending down between the seat stays. after painting it looked to be part of the frame.
You will have to ream the seat tube after you repair it.
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Old 08-20-11, 01:00 AM   #17
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Engineering 101 thats a propagating crack and is only going to get bigger if you dont do anything about it, id suggest a lug but im sure there are some other acceptable less extensive ways to fix it
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Old 01-30-12, 10:39 PM   #18
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I would think that drilling a hole at the end of the crack would help keep it from spreading. Then possibly brazing the crack and filling the hole with silver or brass to finish it off.
Forgot about this thread. This is basically what was done and it seems to have worked! 800+ miles since and the repair has held up perfectly.
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Old 02-09-12, 03:41 PM   #19
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First drill a small hole (Say 1/16 in') at the end of the crack to stop it from spreading further. Later if you want to fix perminantly, braze a piece of wire in the hole and a little over the crack. File the surplus wire sticking through inside the seat tube.
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