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  1. #1
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    Venting for bridges

    What do you guys think about venting the seat stay bridge via a port into the seat stay?

    Do others vent their bridges with this style?

    Any pros/cons of this or other techniques for venting?

    Also, for those of you who create "sealed" tubes what techniques are involved?

    My aim is to make the bridge look clean and minimize the potential for water to enter the frame.
    Attached Thumbnails Attached Thumbnails Venting for bridges-vent.png  

    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  2. #2
    Plays with tools
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    I did most of my bridges that way. It does look clean. The drawback is that you can't get any kind of frame saver in the bridge. I've got two bikes that are done this way that are several years old and have't had any problems.

    I believe most people that seal frames up still put vent holes in and then fill them with silver once all the welding is complete.

  3. #3
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    Don't bother venting it

    Just a careful hand with the TIG welder will do it. Leave an easy to access small spot unwelded, let things cool down a tad, then finish up. I don't use any vent holes anywhere on the entire rear triangle of my frames, no reason to let H20 get in if you don't have to.

    If you're not confident enough to do it my way, do what CF suggests and just drill/fill a tiny hole somewhere inconspicuous.

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

  4. #4
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    Hey;

    I did my last one like your drawing, on one side only. Small hole. Of course, where did I end up with a little piece of slag rolling around? Inside the bridge where I'll never get it out! Don't know how that got in there....

    Walt's cool-off idea is a good one that had not occurred to me, although I've done it... by accident. On my first frame - having gotten carried away and neglecting to DO vent holes - I just drilled a small external hole underneath the bridge and wiped a little silicone in it afterwards.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  5. #5
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    So I am finally doing a rear end as we discussed on this thread.

    Welding the stays as a sealed structure as per Walt's approach is not a big deal but what about later when the frame is in the oven for powder coating. How much pressure are we talking about and is it even a concern?

    One question for Walt (and others), do you have any concerns about the stresses of having a sealed rear end when the frame is powder coated? I assume it is okay to powder coat but I want to check before take the frame to the powder coating guys.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  6. #6
    RCP Fabrication
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    How do you purge the rear end?

    Quote Originally Posted by Walt View Post
    Just a careful hand with the TIG welder will do it. Leave an easy to access small spot unwelded, let things cool down a tad, then finish up. I don't use any vent holes anywhere on the entire rear triangle of my frames, no reason to let H20 get in if you don't have to.

    If you're not confident enough to do it my way, do what CF suggests and just drill/fill a tiny hole somewhere inconspicuous.

    -Walt

  7. #7
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    Don't worry about it.

    Steel tubing is more than strong enough to handle being sealed up and then powdercoated/heated again. You will not make your frame explode. There is absolutely nothing to be concerned about.

    -W

    Quote Originally Posted by febikes View Post
    One question for Walt (and others), do you have any concerns about the stresses of having a sealed rear end when the frame is powder coated? I assume it is okay to powder coat but I want to check before take the frame to the powder coating guys.
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  8. #8
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    Personally I just don't backpurge anything but the BB shell when welding up the rear triangle. If you want some purge gas in the chainstays or seatstays for whatever reason, I'd leave the dropout end just tacked while welding up the BB/ST end, then finish the dropout joinery last.

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

  9. #9
    Plays with tools
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    Quote Originally Posted by febikes View Post
    So I am finally doing a rear end as we discussed on this thread.

    Welding the stays as a sealed structure as per Walt's approach is not a big deal but what about later when the frame is in the oven for powder coating. How much pressure are we talking about and is it even a concern?

    One question for Walt (and others), do you have any concerns about the stresses of having a sealed rear end when the frame is powder coated? I assume it is okay to powder coat but I want to check before take the frame to the powder coating guys.
    If by chance it ruptures in the powder coat process, they did you a favor as it was bound to happen in the field.

    On Walt's method. I have had tube fits tight enough that they've still blown out on me long before the weld sealed them up. Not on a bike frame though. I suspect it's got more to do with how fast you're heating it up. Small air void with heavier tubing that would require more heat is definitely going to cause problems with tight fits.

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