Building first frame (fillet brazed)- Mtbr.com
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  1. #1
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    Building first frame (fillet brazed)

    Hi All,

    Just thought I'd run my plans past a more experienced group so that I go into this project with more know-how.

    My friend has a State Bicycles Trooper 4.0 fixie that he uses as his commuter in Berkeley (CA). It has drop bars and track bike geometry (size 52cm) with a flip-flop hub and horizontal dropouts. The bottom bracket and head tube are threaded.
    Geometry here: https://cdn.shopify.com/s/files/1/02...hart-fixed.png

    I am a mechanical engineer student with an automotive background and have recently gotten a milling machine and oxy acetylene setup in my home garage, and my coworker has a professional-grade frame jig that he is willing to lend me. I have never built a bike frame but I do have some experience with fabrication.
    The plan is to swap all of the components from my friend's bike (including fork) onto a new frame designed and built by me. The only significant departure from their design is to include an integrated seatpost-- i.e. one size fits one.

    We are planning to copy the geometry of his bike, but use 4130 tubing and brass (bronze???) fillet braze the joints. He is an occasional road/crit racer but being that this is his commuter, frame sturdiness should be paramount to ride/handling/weight.

    It would be great to get a nice step by step process of what to do- the best I have found so far is this:
    Wold Cycles
    This is more of an overview, so it would be nice to get a bit more detailed- for example how much of a gap should I leave between the mitered tube and the tube it is going to be brazed to?

    I want to build this frame to practice my fabrication skills and try something new, so I aim to keep the cost low and design simple.
    Given my lack of experience regarding framebuilding, what advice would you give me? Any suggestions would be great. Also, material/parts choice are still in the air, so any comments regarding butted/straight tubing, filler material, flux, vendors, etc would be welcomed.

    Thanks,
    Zack

  2. #2
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    Reputation: Feldybikes's Avatar
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    Go to the FAQ and pick a vendor from whom to buy your tubeset/frame parts. A “real” bicycle tubeset isn’t much more than using 4130 straight gauge. Nova is probably your easiest 1 stop shop if you’re in the US.

    As for a walkthrough, you could do worse than to watch the Pithy bikes videos on YouTube. He’s doing TIG and goes through a lot of steps like building his own jig, but the whole process is there. https://www.youtube.com/playlist?lis...zUrjfIVvvoLC_5

  3. #3
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    Reputation: Eric Malcolm's Avatar
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    Nova Cycles has tubing and in your area.
    The geo for this type of bike is very conservative production style for the average proportion rider. Very safe to copy in other words.
    Your joints for brazing must be tight - no gaps.

    Eric
    If I don't make an attempt, how will I know if it will work?

  4. #4
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    Quote Originally Posted by zake View Post
    The only significant departure from their design is to include an integrated seatpost-- i.e. one size fits one.
    Don't.

    Apart from it being a stupid idea (that seatpost in the conventional joint is pretty usefull) it is pretty hard to keep the tube straight with newbie brazing skills.

  5. #5
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    Never heard of a threaded head tube, but I guess anything is possible.

    I would echo others' suggestions of going with a standard frame kit, probably from Nova. It also simplifies the decision of tube profiles, as there are only so many choices there. I think copying a bike's geo you like is a good starting point. Every builder seems to have their own building style and sequence, so it's hard to recommend the "correct" one. I would look at some of the pithy bikes videos on youtube, and dive in. Maybe stop back here when you have questions. Don't forget to do a bunch of practice brazing joints.
    Myth Cycles handbuilt bike frames
    Durango, CO
    http://www.mythcycles.com

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