Tuesday, August 31, 2010


I was a bit apprehensive about today's tasks. I've never done "semi-wrap" seatstay caps before. And the rear triangle is generally very finicky—once it's set it's set. But it all went as well as could be expected.

Step one was shaping the caps. I did this by dry-fitting everything in the rear triangle fixture and using the brass hammer with a smaller-headed drift. It was incredibly easy, and required no heat.

Then it was time to braze in the seatstays. Using a Doug Fattic contraption to hold the stays in place at the dropout end (an elastic band looped around the dropout and a brass rod sticking out of the SS venthole), I used my regular 56% silver to make my fillets. I remember doing this with the bike on the surface plate in Doug's class, so I did it that way. The horizontal position is pretty ideal.

This step seemed to go very well—but you never can tell until the flux is off.

After I'd done both sides, I moved on to the seatstay/dropout joint—which is both less intimidating and less photogenic.

(Speaking of photogenic, though, note the perfectly white background. This is the projector screen I brought in to mitigate the effects of backlighting. We work with a workbench directly in front of a window. Out the window is very bright white concrete, which can make it very hard to see what you're doing. So I thought placing a white screen behind me while brazing might help. And it did—at least a bit.)

When I got home I soaked off the flux, and was pretty happy with what I saw. My silver fillet is absolutely perfect on the drive side: I kept all the filler on the lug (none crept on to the tube), and the fillet is gap-free:

On the non-drive side it's a bit clumpier but still really good.

I even managed to keep the points more or less symmetrical. (And I like that fairly slight amount of wrap).

There are a lot of ways to screw up the seatstay caps, and there aren't many ways of getting in there and fixing it if you do. I'm really happy I managed to do this cleanly. Now the bike is pretty much done! Just a seat stay bridge (I think I'll skip the CS bridge) and I think a set of water bottle bosses. Then some lug filing and cleanup on the dropouts.


721sandwiches said...

Wait... how many frames have you built? Seatstays: Naaailled it!

Why skimp on the chainstay bridge? (To me that looks like something's missing.)

Maybe I'm not all there though.

AH said...

This is frame #2. Hopefully I can replicate this down the road... I did nail it!

From what I've read and can figure, the CS bridge isn't doing much on a short-chainstayed bike. And every bike I have has one, so I feel like doing something different...