Reason for unusual weld under TT ?- Mtbr.com
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  1. #1
    Tantrumcycles #1
    Reputation: Gunnar Westholm's Avatar
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    Reason for unusual weld under TT ?

    Is there anyone who knows the reason for this two short lines of weld just behind where TT and DT meets on the Instinct Alu frame?

    Is it holding some kind of reinforcement on the inside? Or is it just plain welds on the surface to evening out stress in the material after welding, to avoid cracks to form?
    Is there any history of cracks forming in this area on older frames without this weld?

    Sent fra min Moto G (5) Plus via Tapatalk

  2. #2
    Rocks belong
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    It's clearly intentional, you can see it on the stock photos on RM's site

    Reason for unusual weld under TT ?-untitled.jpg
    I like 'em long, low, slack and playful

  3. #3
    Tantrumcycles #1
    Reputation: Gunnar Westholm's Avatar
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    No doubt it's complete intentional yes as it's perfectly symmetric left and right side.

    But why??? Is it done to seal some cuts done prior to welding the TT to the DT? I imagine it could be for releiving stress due to material changing shape and shrink after welding?

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  4. #4
    Rocks belong
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    Quote Originally Posted by Gunnar Westholm View Post
    No doubt it's complete intentional yes as it's perfectly symmetric left and right side.

    But why??? Is it done to seal some cuts done prior to welding the TT to the DT? I imagine it could be for releiving stress due to material changing shape and shrink after welding?

    Sent fra min Moto G (5) Plus via Tapatalk
    Who cares. Ride the snot out of the bike and have fun!


    (I am curious though. Oh well. See above.)
    I like 'em long, low, slack and playful

  5. #5
    mtbr member
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    You might want to cross post in the frame building forum. Bet they could tell you or at the least hazard the most believable guess.

  6. #6
    Tantrumcycles #1
    Reputation: Gunnar Westholm's Avatar
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    Quote Originally Posted by 06HokieMTB View Post
    Who cares. Ride the snot out of the bike and have fun!


    (I am curious though. Oh well. See above.)
    Hahaha I'm not gay or a girl so of course I care about things like this! ;-)

    I would also have tried my best to ride the snot out of one, but that's hard to do when I don't own one. We have a few of them at the bike rental I work in. And I might keep a used one in the end of this season.

    The main reason I care about this is we have a few bikes from another brand that have cracked in the same area as this weld..

    Cross posting was a good suggestion. I will do that




    Sent fra min Moto G (5) Plus via Tapatalk

  7. #7
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    My wife's Pipeline is that way too (well, of course...because it is the same frame!). I've wondered about it, do not know for sure. I thought perhaps it creates a better weld to have a bit of "lead in"...but the other welds aren't that way so.....

  8. #8
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    That is indeed weird. It won't be a structural weld to hold an internal gusset. It's too small. You don't add welds to relieve stress is alloy. You Normalize then heat treat.

    My guess is that this is covering a mark that is create during the production process.

  9. #9
    Tantrumcycles #1
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    Quote Originally Posted by plummet View Post
    That is indeed weird. It won't be a structural weld to hold an internal gusset. It's too small. You don't add welds to relieve stress is alloy. You Normalize then heat treat.

    My guess is that this is covering a mark that is create during the production process.
    I agree on the gusset thought.

    My thought regarding stress relieving was it could be cuts prior to welding to avoid heat transfer down the TT to an area that could be prone to cracking when the leverag forcese from the fork transfers into the frame triangle trough the HT.

    I would be weird if it's just for covering som kind of marks when/if no other frames got something similar..

    I'm waiting response from Tech support. If no success there I will borrow an endoscope and investigate next time a fork needs to come off one of the rental bikes where I work!

  10. #10
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    It relieves the stress built up in the weld. It's as simple as a few extra mm of weld bead...
    Director of Product
    Rocky Mountain Bicycles

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