Tuesday, October 11, 2011

Let the brazing begin

In the end, it was the old-fashioned kind of social networking that found me someone who could teach me to braze. A fellow Xtracycle owner, who "knew" me from seeing me ride around town, happened to be working in Velocity Cycles the day I dropped in for a tweak on the Ruby. His name was Jake, and he remarked that he'd seen me on the Xtracycle, riding around, and didn't I also own a Salsa Casseroll? One bike led to another, and I mentioned that I was in the process of making my own frame, but would like to find someone to show me how to braze. And thus it was that he mentioned Will, from whom he'd bought a house. Will, he told me, was a metal sculptor, a colleague from school in the Department of Art, and a fellow cyclist. Jake was sure he'd be interested in my project.

It happens that I've met Will before at a neighborhood party, but we didn't really converse then (because I am fundamentally shy, and would rather stuff a rabbit up my nose than to make small talk with someone I don't know; yes, I realize that this is a problem). He stuck in my head, though, because he was wearing a kilt, an attire he comes by honestly, since he hails from the British Isles.

Anyway, I fired off an email to Will, outlining my project, and he said he'd not only be happy to help, he was interested in building a frame one day himself. So he came over the shop one night last week--wearing regular clothes instead of a kilt--and I had my first lesson in brazing. Here's Will, who, as it turns out, is easy and pleasant to talk to:

Brazing is like soldering, but brazing uses higher heat and a stronger filler for a stronger joint. In this case, I am using MAPP gas and a MAPP torch, both of which are available at any hardware store. MAPP gas, which comes in these yellow canisters, burns much hotter than propane. I borrowed this torch from my neighbor Tom, but it is causing me some wrist pain to hold the whole shebang, so I am currently looking to replace it with a torch that has a hose attached:

Will, who has been brazing since he was sixteen, brazed the first joint--the seat tube to the bottom bracket--to show me how it is done. We first cleaned all the surfaces to be joined with 400 grit sandpaper, and then wiped with mineral spirits to remove any oxides. Then the end of the seat tube and bottom bracket lug hole were painted with white flux and fitted together. Heat was applied and the filler, 56% silver (called Silver 56) was drawn into the joint through capillary action (or, as Will called it, ca-PILL-ary action):
The filler leaves a smooth meniscus around the edge of the junction between the tube and the lug. This is called the "shoreline." When properly applied, the filler goes all the way through the joint and comes out the other side. (That white coating is the left-over flux.) Here it is with the flux cleaned off:

Unfortunately, but not unexpectedly, it was not as easy as it looked. Here is my first effort at brazing:

The flux on the lug itself and the head tube (the vertical tube) have turned black, which means that I exhausted it before the filler could be drawn into the lug. When the flux was cleaned off, I could see gaps in the shoreline, as can be seen here, in the small gap at the top left of the junction between the lug and the down tube (click to zoom in, should you so desire to see the gap more easily):
So at Will's suggestion, I cleaned off as much of the oxidation as I could, and then over the weekend, I had another go at it, using a lot more flux, with better results:

It is a little hard to see in the photos, but there is a solid shoreline all the way around, and I'm confident that I got enough silver in there to fill up all the void space, making it a strong joint. The excess filler can easily be cleaned off with files and a Dremel tool.

Speaking of the Dremel tool, I've never really been a fan. In fact, it has seemed for the longest time to be a silly, superfluous tool. I never could figure out what it was good for that a hacksaw couldn't do just as well. But between using it to cut and fit the miters, and now to grind down the excess filler on my blotchy brazing efforts, I have to say that I have fallen in love with this tool.

In fact, I'm so taken with the amazing utility of the Dremel that I've gone ahead and had one of my hands replaced with it. See what you think:

It should be great for brushing my teeth. And as for using it in the kitchen to whip up mashed potatoes, well, I think I need hardly say more...

I still have the top tube to seat tube and seat tube to bottom bracket to braze to complete the main triangle, but here is what it looks like so far when the other tubes are dry-fitted to the brazed in order to check the angles:

By the way, in case you missed my post yesterday announcing the completion of the Bike Garden Challenge, here it is, with all the skinny you need for sending in your pledges. Thank you again, everyone, for all your support.


  1. Why of course you would have met your kilt-wearing/ brazing friend at a neighborhood party. Naturally :)

    P.S. Your photoshopping skills are awesome.

  2. Funny - I use a dremel at work (I am an RN).

  3. Hi very good post, got a very good information about brazing. Thank you for the post.