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  1. #1
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    tiny gusset crack repair

    my Soma Juice Tange Prestige has been developing a crack at the base of the HT/DT gusset. they've been rumored to crack all the way through the DT there.



    I swapped eveything back onto the previous commuter frame (like it better for commuting anyway) but now the Soma is un-sellable and un-useable.





    Should I sand it down myself to get a look at what's going on before looking for a repair guy? How involved (i.e. expensive) would this potentially be? I know it will likely cost almost as much as the frame did (used) for me... but I can't bare to throw away stuff.
    Any recommended frame builders in the Grand Junction, CO area?


  2. #2
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    Sand it down. Wouldn't be at all surprised if that's just paint flaking.

  3. #3
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    Send it for warranty?
    Guillaume

    Cycles Golem

  4. #4
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    Odd place for a crack. I'm guessing it's the edge of a HAZ on the thin tip of the gusset.

    Since the end of the gusset isn't doing anything and the crack could continue propagating, if that was my bike and I had no hope of warranty I would actually just file off the end of the gusset to get rid of the crack. Assuming I was really sure the crack hasn't gotten past the weld.

    However, that's not my bike, IANYF, etc...

  5. #5
    RCP Fabrication
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    Both sides are cracked? I think its time to scrap it.

  6. #6
    Squelch the weasel.
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    Trade a frame repair for a custom made frame pack. Those are nice looking!

    Blaze Bicycles is in Moab: Blaze Bicycles -- Handcrafted Custom Steel Bicycles, Moab, Utah
    Last edited by JaquesN; 07-19-2012 at 01:53 PM. Reason: forgot to mention local framebuilders

  7. #7
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    That weld shouldn't have carried around the tip of the gusset like that. It should have just stopped at the end of the gusset...well, too late for that now. Dr. Welby's advice is sound: file/ grind off the cracked end of the gusset. If the crack hasn't already propogated into the weld the bike will be fine for years. If it has gotten into the weld...well, you'll be glad you didn't spend a lot of money on a fix.

  8. #8
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    I'll sand off the paint around it and take a good look at the area, then put up some pics. This frame is second hand so no chance at warranty.

  9. #9
    Relax. I'm a pro.
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    I'm not an engineer, but BMX frames moved away from this design many years ago. Shitty design.
    Instagram: @antoine1000
    http://tfwo.tumblr.com

  10. #10
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    Good example of why curved top tubes suck. The lack of triangulation makes the DT do all the work. Since the gusset makes the joint stiff, the 1st weak spot where all flexing begins is at the end of the gusset. Welding it will just make it crack after the weld later. Put in a straight top tube to fix it.

  11. #11
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    I sanded down the affected area and see no cracks. There might be a little tiny something, but now I want to take it in to the engineering building and try out magnetic particle inspection on it to see if there are any cracks.

    Yeah, I don't like bent top tubes, they look rather dumb to me and reduce frame bag volume, but I found a good deal on this one (at least if it didn't decide to fall apart).

    So, new TT and DT? File off the gusset tips and ride it til it breaks for real? Hang it on the wall and forget about it? Sell it cheap to one of you frame builder guys to repair and keep?

  12. #12
    Randomhead
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    I have been thinking you could file away the crack and it would stop any crack growth. That assumes it hasn't gotten into the tube already.

  13. #13
    gran jefe
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    after filing, sand it nice and smooth before you do the mag particle inspection or the penetrant dye test. it will make it easier to be sure whether there is a crack or not.

  14. #14
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    Must do a dye test, mag won't work on AL. The crack probably is not into the tube yet, the edge of the gusset is a nice stress riser for the crack to start.

  15. #15
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    Quote Originally Posted by TacoMan View Post
    Must do a dye test, mag won't work on AL.
    That bike is steel - look at the dropouts.

    (Edit) D'oh! or read the first post - "Tange Prestige"

  16. #16
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    1. Yes its a steel frame. Magnets will work.
    2. Yes I'm already planning on sanding it really smooth before testing so the sandpaper scratches aren't
    a visual issue.
    3. Since the crack probably isn't into the tube yet, filing off the cracked part of the weld/gusset is a good easy fix, but wouldn't that just delay the issue, if the stress concentration issue is still there? There are two parts of the stress concentration, and I'm unsure which is more important. There's the narrowness of the gusset and weld bead as it necks down to the point at the end of the gusset, there's also the fact that the gusset will want to act as a fulcrum here when the frame flexes in the vertical plane, so the tube gets bent back and forth over the end of the gusset. Doing mag particle testing before filing and after filing could be very instructive, then riding it some and checking again. Maybe even if this frame is slowly dying (no NDT pun intended), I'll at least get my money out of it for some hands on enginerd/weld inspection and repair experience.

  17. #17
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    Filing off the cracked corner will do one of two things:

    1. Solve the problem entirely.

    2. Delay the eventual failure of the frame.

    Why? Let's do a little speculating about why the frame cracked where it did. As I mentioned earlier, the weld bead should have stopped right at the end of the gusset. Instead, it got carried around the end of the gusset, maybe in order to hide any crater. What that extra few seconds of welding did was dump an immense amount of heat into the gusset tip that didn't have anywhere to go. That tiny little point of metal is probably the part of your bike that's the hardest, and therefore the most brittle.

    The reason I'm saying that so confidently? Take another look at where that crack started: at the point on the gusset stamping. It's not just the internal corners that are stress risers. Get rid of the crack and you'll also get rid of the over-hardened part of the gusset. Put even a tiny radius on your new corner and it won't crack again.

    I'd still do my respray in a nice light color to make it easy to find a crack if it reappeared, though. Have fun with the NDT.

  18. #18
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    Well since it is steel, it is worth a shot at repairing.

    I would make a diamond shaped doubler from tube about 2-3x tube dia. long and the width of the gusset. Weld one end into the un-welded part of the gusset, and then fully weld the rest along the DT. The diamond portion along the DT should be 30 deg. angle per side. This will spread the load farther down the tube.

  19. #19
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    A while back I sanded the paint off the cracked areas, and can't see any cracks in the metal. Since anything that might be there is so small, that's why I want to try magnetic particle inspection before and after filing the cracked part off.

    In other news, one of my engineering professors is wanting to try a project to measure peak loads and low cycle fatigue in frames under real riding conditions. The plan is to put several strain gauges on the bike along with a data collection widget, then go ride hard for a while and see what the data looks like. Getting it calibrated will be one of the challenges.

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