Sunday, July 27, 2008

Day 8: Tacking and Brazing the Front Triangle

After a day of laying around yesterday, I was dying to get back in to the shop and do some more work. Indeed, I sneaked in last night at 9 and did some filing on my fork blades. I stayed in until 11.30, and the time flew. Filing is going to take a long time.

This morning as I ate breakfast I read the chapter on brazing the front triangle in Doug's framebuilding manual, and "visualized" my plan for the day. Before noon I would spot up the full front triangle in the jig; between lunch and dinner I would braze up all the lugs; and then after dinner I'd return to my filing.

It didn't get quite that much done, but it was still a good day, and one in which I made lots of tangible progress. So. First I tacked the frame together in the jig. Each of my lugs meets its two tubes in four points: the lower headlug, for example, touches the downtube in two points and the headtube in two points. When you spot braze the frame, you clamp it down in to the fixture and then make little spots brazes on two of these four points, one joining the lug to each of the two tubes it joins together. When these are done, you take the frame out of the fixture and align it. Doug's system for doing this is visible in the first photo. (Basically, you clamp the bottom bracket shell into a faux-bottom bracket on an alignment table and use a little height gauge to make sure every tube is equally high off the table.)

When the alignment is ready, you prepare to braze the lower headlug. So, you spot braze the two remaining points on the lug, let it cool, and then realign the frame. Once it's aligned, you get ready to braze the lug. Doug gave each of us a practice lug to try out before we actually did our own (the practice lugz were factory reject Richard Sachs Rene Singer lugs -- they were nice!). It wasn't very much harder to do than the other joints we've worked on, but it was cooler — it's very satisfying to see the silver actually traverse the miter from one tube to another and peek out the other side of the lug!

Unfortunately my "actual" brazing didn't go so smoothly. I hadn't completely sandblasted the inside of the lug, so the silver didn't want to move as it should. This was a "bad" thing, I guess, but it also signaled something good: I could tell that the silver wasn't moving the way it should. Anyway, I called Doug over to finish the lug up, and walked me through it. That's him working on my bike up above.

When that braze was done, I let the frame cool down. Then I checked the alignment. Then I spot-brazed two more spots on the upper headlug. Then I let it cool. Then I checked the alignment, which was actually pretty far off. I took the necessary hour or so aligning it. Then I brazed the upper headlug. This was my best one yet: I'm really beginning to feel in control of the torch, and can move the silver where I want it. I think I've had decent "feel" for things from the start (everything has gone so much easier for me than for Dan and Robert!), but it's really getting fun now.

As for Robert and Dan: Robert has tacked his frame and is ready for his first lug-braze tomorrow morning. Dan is busy taking apart his incorrectly spotted frame to fix its problems (he's insistent on using 700c wheels!). He's had to cut out the down tube and get a new one, and also shorten his head tube. He is indeed in the shop right now doing that.

Tomorrow I'll finish my front triangle and maybe also finish filing my front and rear dropouts. Then it will be time to fiddle with chainstay length and seatstay caps. My frame is really beginning to look like, well, a frame!

[More photos here.]

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