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  1. #1
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    Any reasonable way to ovalize seatstay after frame is built

    Hi all,
    Does anyone know of a reasonable way to ovalize a seat stay once the frame is built? Mine are somewhat stiff for the application (they're required to flex), and this might be one solution to the problem.
    They're titanium.

  2. #2
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    Perhaps a set of dies made of wood and padded with rubber, then pinch gently in a suitable vise? I've straightened/un ovalized cromo that way, not sure on ti.
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  3. #3
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    You will have a really hard time doing that - ti springs back like crazy and you'll need a heck of a press to ovalize it significantly when it's already on the frame.

    Can you explain the problem? I'm curious why the *seatstays* need to flex.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
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  4. #4
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    Sledge hammer?
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  5. #5
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    Quote Originally Posted by Walt View Post
    You will have a really hard time doing that - ti springs back like crazy and you'll need a heck of a press to ovalize it significantly when it's already on the frame.

    Can you explain the problem? I'm curious why the *seatstays* need to flex.

    -Walt

    It has rear suspension with the "seatstays" and chainstays solidly connected, i.e. no pivot at the dropout, relying on the titanium to flex instead. It's basically a replica of a Funk La Ruta; the 'seatstays' connect solidly to the shock and this transfers a lot of lateral (and up-and-down 'lateral') forces to the shock.

    I spec'ed 19mm x 1.3mm seatstays (version 1.0 can't be perfect, can it?), and I think the forces on the shock are a bit much, so, I'm trying to lessen them.

    I can't seem to get my ipad to post pictures here right now, and my computer is broken at the moment. You can see a picture of it here though:
    My Ti full suspension 29er+

  6. #6
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    Why would work hardening the stays make them flex more? Maybe I'm confused, but it should make it even stiffer.

  7. #7
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    Your only option is to remove the rear end and put one on that's more to your liking.
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  8. #8
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    It looks like it has flex pivots in the seatstays already?

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    Ah, ChiTi. You're on your own, dude. If you want it done right hire Funk or someone else reputable.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  10. #10
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    Quote Originally Posted by jay_ntwr View Post
    Why would work hardening the stays make them flex more? Maybe I'm confused, but it should make it even stiffer.
    I'm no expert, but I don't think hardening changes the stiffness of a metal.

  11. #11
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    Quote Originally Posted by Mountain Cycle Shawn View Post
    Your only option is to remove the rear end and put one on that's more to your liking.
    Cool Ferrari!

  12. #12
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    Quote Originally Posted by dr.welby View Post
    It looks like it has flex pivots in the seatstays already?
    Yes, it does. They do not do a whole lot right now, at 5 mm thick. I think my plan is to take them down to 3 mm thick, that will decrease the stress on the shock by 60%; the problem is that the stress in the flex pivots will approach the plastic deformation point of the metal according to calculations I've done in some beam deflection calculators, and then I'd have fatigue failures.

    I think it will be alright though; once I take those down to 3 mm, I can 'pre-bend' them a little, and maybe limit travel a little, and all will be good.

    But, it might even be fine how it is. It just seems like a lot of stress on the shock - it's about 35 lbs of lateral force on the shock at full travel right now.

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    Quote Originally Posted by Godlikedog View Post
    They do not do a whole lot right now, at 5 mm thick.
    Seems like ovalizing the stays is going to do about an order of magnitude less.

  14. #14
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    Quote Originally Posted by dr.welby View Post
    Seems like ovalizing the stays is going to do about an order of magnitude less.
    Shouldn't an ovalized tube's stiffness vary approximately with the square of how much you squash it? I mean if its a 19mm tube and I ovalize it down to 15mm x 23mm (approximately), the stiffness difference should be around the ratio 15^2/19^2, which is about 62%.

    Doing some more calculations I get that it's about 69%.

    Well, it's not gonna happen. Maybe the chainstays though, hmmm .......

  15. #15
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    Quote Originally Posted by Godlikedog View Post
    Shouldn't an ovalized tube's stiffness vary approximately with the square of how much you squash it?
    I meant an order of magnitude less than flex hinge you already have in there.

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