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Thread: CSI lugs

  1. #1
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    CSI lugs

    Has anyone noticed this style of lugs before? This is a first for me. How is is done?
    Attached Thumbnails Attached Thumbnails CSI lugs-_mg_0811.jpg  

  2. #2
    Spokane, Washington
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    Your CSi has a 1 1/8" headtube and those are what Serotta termed 'faux lugs'. The CSi was Serotta's top-tier steel bike and was known for its lugs. There were no lugs big enough to accommodate this 1 1/8" headtube so those junctions were fillet brazed and the ''faux lugs' were carved in. The rest of the bike was lugged as normal.

    Here's another example.
    Attached Thumbnails Attached Thumbnails CSI lugs-csi3.jpg  
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    thanks Dave. how does that carving work?

  4. #4
    Spokane, Washington
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    Quote Originally Posted by RJohn
    thanks Dave. how does that carving work?
    I'm not quite sure what you mean "how does that carving work?" It's not a functional piece. The head/top/down tubes are joined by fillet brazing, which in your case is expanded well beyond the tube junctions. Then excess braze is removed, by files/sandpaper/emery cloth etc., and the edges that are left resembles the shoreline of a lug. It's an appearance thing only, no function.

    This pic, lifted from Kirk Frameworks website (http://www.kirkframeworks.com/) shows a fillet brazed headtube. Now imagine too much brass being applied and some removed to make an edge on the headtube, and you may be able to see how Serotta could make these 'faux lugs'.
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  5. #5
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    OK. Now I get it. Sure seems like a lot of work though. No wonder I have never seen this technique before.

  6. #6
    Spokane, Washington
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    Quote Originally Posted by RJohn
    OK. Now I get it. Sure seems like a lot of work though. No wonder I have never seen this technique before.
    It was a lot of work but the reason that Serotta did it was because the CSi was their flagship and it featured lugs. The next bike down in their line was the Colorado III; great bike, less expensive and didn't have lugs. So the extra work was done to keep the differentiation between the two.
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  7. #7
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    Hey,

    Fun to see these bikes again.

    The construction technique is a bit unusual and at it's core a purely pragmatic deal. We wanted to use tube sizes and/or shapes that we did not have lugs to fit so we combined traditional lugged construction with fillet brazed construction.

    In the case of the green bike in the first post the head tube lugs were extensively modified by cutting off the sockets normally used for the top and down tubes. The top and down tubes we wanted to use would not fit in the sockets of the lugs so we removed the sockets. So with the sockets removed we then are left with a sleeve or sorts that slips over the head tube. This sleeve has a hole that the top tube/down tube used to slip into and this hole is then enlarged so that the new oversize top/down tubes can fit into it and come in direct contact with the headtube.

    So what you end up with is the remainder of the lug wrapping the head tube to reinforce it and the top/down tube going through the modified lug to meet up directly with the head tube. When the joint is brazed it's a combination of lugged and fillet brazing. The remainder of the lug is brazed to the head tube just like a normal lug and then the top/down tube is fillet brazed onto the modified lug sleeve.

    In the end you have a very strong joint and a reinforced head tube and a mix of looks. There really is no stronger way to hook two steel tubes together. It is extremely time consuming and takes some special skills but once you get the hang of it it's actually fun to do.

    I hope that explains the process well. I'm still on my first cup of joe for the morning so who knows what the hell I've written.

    Dave

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    Thanks to Dave and David. I can understand the process much better now. David, you seem to have a lot of knowledge about this technique. Did you work at Serotta? When you say we, I'm assuming that you did.

  9. #9
    Spokane, Washington
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    Quote Originally Posted by RJohn
    Thanks to Dave and David. I can understand the process much better now. David, you seem to have a lot of knowledge about this technique. Did you work at Serotta? When you say we, I'm assuming that you did.
    David Kirk worked at Serotta for about 10 years. Built a lot of famous race frames and was also the head of Serotta's R&D. Did a lot of good stuff while he was there and now has his own shingle: http://www.kirkframeworks.com/ . A really great guy. Builds bikes too.
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  10. #10
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    Quote Originally Posted by RJohn
    Thanks to Dave and David. I can understand the process much better now. David, you seem to have a lot of knowledge about this technique. Did you work at Serotta? When you say we, I'm assuming that you did.
    The Big Man Dave T nailed it.

    I worked at Serotta from 1989 - 1999. I started in the production shop and ended up being the R&D dept where I designed all the new product, tested it, developed the tooling to make it and then taught the guys in the shop how to do it.

    Now I do the same thing but in the mountains of Montana and by myself.

    It's good work.

    Thanks for asking.


    Dave

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