Friday, July 25, 2008

Day 6: Lots of Brazing by Me... Disaster for Dan

Each of the three of us wanted to get lots done today. Doug is a Seventh Day Adventist and observes a Saturday sabbath, so there's no activity in the shop from sundown Friday to sundown Saturday. We we're all eager for the day off tomorrow (timed well for the Tour-deciding time trial) but were also very eager to finish off as much as we could.

My first task, which I dreamt about all night last night, was brazing the front dropouts to the fork blades. My dropouts are slotted Suntour GSes with eyelets — I got them with my rear dropouts from David Wages of Ellis Cycles. Robert is using the Henry James plug-type dropouts, which can be silver-brazed into the stays. But mine need to be brass brazed, since (as I believe I said yesterday) brass fills the gap between the dropout tab and the circular stay. The brazing proceeds in two steps: first you heat up the tab until it's red, and melt the brass where it meets the stay, drawing it into the stay with the heat until it fills up the stay; then you add brass above the top of this pool, creating a pile of brass to file down into a smooth scallop. This all went fairly well, though the fixture created an awkward angle on one of four sides and Doug had to complete it for me. (There are, apparently, two types of students: ones that want to do everything themselves and ones that don't mind passing the torch to Doug when things get in a mess.)

Next up was brazing the bottom bracket to the seat tube. First I did a practice braze, which went fairly poorly, and then the real thing. The trick is to get the seat tube coming out straight from the bottom bracket shell. So first you tack the seat tube to the BB shell in one spot. Then you bend it until it's straight. Then you spot the other side, and bend it again if it has deformed. Then you braze it up. My tacks were sloppy, but the rest was fine. That's my flame working away at the top of the post (Doug took the photo).

The last thing was cutting the chainstays to length and brazing the rear dropouts to the chainstays. (I'm using Campy 1010A dropouts from which I have filed off the derailleur tab and am currently engaged in re-shaping.) I decided on a length of 450mm, which is nice and long and leaves plenty of room for 26mm tires and fenders. I actually thought I had cut them a little short at one point and thought I'd need to pay for another set of stays, but then I tried them out in my wheel, which I brought along, and they fit fine. This near miss served to remind me once again not to hurry, even though I was dying to get this one last task done before sundown — if I could, I'd be officially "on schedule."

As it happened, I did. Indeed, I put the dropouts on an axle, got them square, set them in the stays, and did undoubtedly my best braze to date. The brass filled in perfectly and stayed where it should have, and then I added just the right amount. Doug was busy helping Robert with a braze, so I did it by myself — which was nice. But just as Doug was beginning to admire my work, I noticed that one dropout was not centred in the stay. So he had to heat the whole joint back up, melting all my good work, and re-center it. I think the gods wanted to correct my brass-brazing pride.

Then came the letdown of the day. On the very first day of class, Dan made an error in calculating the clearance needed on his fork. Instead of putting in the wheel radius (which includes the tire) he used the rim radius. So he has about 20mm too little clearance. He has since tacked his entire front triangle, and it's wrong. His choice is either to un-tack his entire frame and perform some sort of surgery on his lugs or else use 26" wheels.

In the meantime, I'll be filing scallops into my dropouts...

[More photos here.]

2 comments:

Pete said...

Very cool stuff, thanks for posting!

Anonymous said...

I'm really enjoying this! I took a class from Doug around 1980 and still ride the bike I built then. He's a gifted teacher and framebuilder.