Tuesday, April 2, 2013

"B" is for Brazing Bicycles

For this installment of my A to Z series about materials, engineering, and making stuff, "B" was to be for "Bicycle Materials," something I've been interested in since I got into bicycling and began working on my engineering degree twenty-five years ago.  (Yes, I did finish).  But it's far too expansive a subject for an A to Z blog post, and these folks here and here do a better job of explaining it than I could anyway.

So instead, I'd like to narrow the topic down to what the guys in the pictures at the above links are doing, which is called "brazing." This is not to be confused with "braising," which I imagine someone is explaining at this very moment in a cooking blog somewhere. 

I remember when I was a kid in the late '70s talking to another kid about bikes (BMX bikes, natch) and him talking about how his bike was great because it was made of "alloy" instead of steel and how it was also better than steel bikes because it was welded, and the steel bikes, his father told him, were "soldered."

Rivendell Seat lug.  Tubes brazed into it and seatstays onto it.
This used to be my bike.
Later, I figured out that by "alloy" he meant aluminum alloy (steel and aluminum bikes are both constructed of alloys, which are simply mixtures of metals), that steel is arguably the best all-around material from which to make a bicycle frame and and that his dad was full of poo-poo.  By "soldering," he really meant "brazing."

Saying the steel bikes were soldered implied that they were weak, structurally unsound, because soldering is a low strength proposition.  As any BMX-riding electronics geek can tell you, soldering is a secure connection for wires and such that aren't under a structural load, but it's not for bunny-hops and double-jumps.  But brazing is a great way to make a strong bicycle frame that gives up nothing in strength to welded aluminum.

Like soldering, brazing involves connecting two or more metal objects with molten metal, but brazing is more precise.  With brazing, the parts are close-fitting and capillary action draws the molten metal into a thin gap between them (recall that when you dip a corner of a sponge into water, capillary action is what draws water up into the sponge, even against gravity).  In bicycle building, the parts are a steel frame tube and connections, called lugs, or other fittings.  The framebuilder liberally brushes a liquid called flux onto and all around the surfaces to be joined, which protect the metals from oxidation and other contamination.  He or she then carefully applies heat to the joint with a gas torch and touches a metal wire (silver alloy in higher-quality frames) to the gap between the parts.  The silver is melted and drawn into the gap.  Brazing is a fairly simple process, but one that takes years to master.  Good framebuilders know just how much heat to apply - too little and the gap won't be completely filled, too much and the steel will be weakened.  They also know where to apply it - the silver actually flows toward the heat source, so by directing their torch, they can make sure the gap is evenly and completely filled.  The close fit of the parts, the large surface area of their interface and the metal filler make an extremely strong joint; failures of brazed joints in well-made frames are beyond rare.  You'll pull a tube apart before you pull it out of the socket of a properly brazed connection.

As with many crafts, the brazed steel bicycle frame has been replaced in the mass market by cheaper materials and methods that are marketed as "improvements" to buyers, especially new ones.  But, as with many crafts, the professional bicycle framebuilder makes something of extremely high quality that is infused with his or her passion and can easily outlive its owner and be passed on to his or her children.

 http://www.a-to-zchallenge.com/

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20 comments:

  1. Well, I'll be darned! I had given no thought to the differences in bicycle frame building. Now, I'm off to do some braising. xoA

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    1. Ha, great! I suddenly have a craving for lamb shanks and beef tips. Thanks for your support.

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  2. very interesting. I don't know anything about bikes

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    1. Thanks, April. I think one of the things that make them interesting is the passion of people who make them and their dedication to their craft.

      Thanks for stopping by!

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  3. I am so grateful that you are finally sharing your incredibly vast knowledge with us. Your intelligence and variety of interests makes me feel like a loaf. Keep it up; it's a great payback for me hovering over you like a runaway fugitive to get you to write.

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    1. That's very kind of you, Dana. A lot of people would call me a dilettante, but I know you to be much more charitable than that. You're a great coach. Thank you!

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  4. Very interesting, and you explained it so even I could understand!

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    1. Thanks, Joan, glad to hear it, but don't sell yourself short!

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  5. Brazing and soldering techniques aside, I was pleased when the post resolved into a reflection on the master craftsman creating a work of art to be passed down to succeeding generations. Nice touch, Jerry. I like it.

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    1. Thanks, Dennis. My intent with all of these is to start with a seemingly prosaic subject and tie it into the larger world. I believe in a Creator who made everthing with a unity and an overarching purpose, and because of that, everything is related, sometimes in surprising ways. Thanks for your time!

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  6. Who knew brazing could be so interesting? Like the information and your writing style. I also understand about being "tricked" into the A to Z Challenge. That happened to me last year. Not sure why I signed up for the insanity again this year??

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    1. Aw, you know why. The same reason I eat artichokes; they're good for me, delicious and fun. Thanks for the kind words.

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  7. Jer thanks for your comment on my post A is for Abode - and you are so right, Christ is the best place to have my heart. Hope you have a blessed day.

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    2. Thanks, Alice. You also!

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  8. NICE BLOG!!! Your blog is very informative for us. I would really like to come back again right here for likewise good articles or blog posts. Thanks for sharing a nice information.
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  10. Brazing is a most awesome B word! My husband solders stained glass, and brazing sounds exponentially strong!

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    1. One could braze a stained glass window, but it wouldn't make much sense to go to the extra work since soldered joints are stronger than the "weak link," which is the glass.

      Thanks for stopping by!

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