Thursday, July 31, 2008

Day 12: Brake and Chainstay Bridges

The first I did this morning, before Doug had even come in, was to braze my second seatstay to the seatlug. Then I brass brazed the seatstays to the rear dropouts. All this went quite smoothly. Unfortunately, though, when I put my nearly completed frame in the Anvil fixture to set up the latter braze, Doug noticed that my bottom bracket drop was way off — 90mm instead of the 75mm I wanted. When we slid the dropouts to the middle of the long 1010a dropout slot, it was still around 83.5. The thought passed through my mind: "Well, I guess I won't be staying up all night filing the lugs. This frame is un-rideable." Since it's a fixed gear and you need to pedal through corners, low bottom bracket drop is hardly desirable.

The problem came from the second day of class. Doug used my frame as the example of how to set up the design fixture. And, in the course of doing so, accidentally set it lower than he was supposed to. I likely would have double-checked all my measurements if I had done it myself, but I didn't think there was much point since Doug did it. Of course, little mistakes like this happen easily when one is concentrating hard on doing something like teaching a lesson, and I should have double checked. But anyway, it's not the end of the world. My desired drop was based on 700x25 tires and 170 cranks. I was planning on using 700x26 and 167.5 cranks anyway, but I wanted to introduce a bit of a failsafe — and I've used all of it up now. I'm pretty sure everything will be fine. I'll just be sure to situate my rear hub toward the front of the dropout slot.

After that I spent the rest of the day mitering and working on my bake and chainstay bridges. It took a long time but it was fun. I found the time to braze water bottle mounts into each of them for easy and clean fender mounting. Doing little things like that makes me feel like a "real" builder of custom frames.

Robert's bike is now done, sans filing. Doug put most of the braze-ons on for him, which was the only way of ensuring his frame would be finished. It looks great. Dan is certainly on his way, and is right now designing a rear mount for his disc brakes.

I'm about to head back into the shop for a few hours to do some filing. I'm not going to make my lugs look perfect, but I will at least clean them up and get the casting marks off. And I'll put scallops in my front dropout joint and seatstay/dropout joint. If I can manage it, I can do some final lug filing back home. Tomorrow I'll do the braze-ons. (It will be weird without Robert there!)

(NB: when I said in yesterday's post that Doug brazed three lugs, I meant three joints — I'm not quite so pathetic as to arrive at framebuilding class unwilling to actually build any part of the frame myself!)

[More photos here.]


NB said...

So, pictures of the finished thing

NB said...

erratum: [ins.] ?