Tuesday, May 4, 2010

Seat Tube to Bottom Bracket

The second time was the charm, I'm happy to report.

I was extremely careful about two things this time. Firstly, cleanliness of the joint. I sanded the joint with 80 grit shop cloth, then cleaned it out several times with methyl alcohol on a J-Cloth. I cleaned not just the surface of the joint itself but also the adjoining areas. I did the same to the tube, inside and out. Secondly, flux. I put it everywhere. On the tube, in the shell, inside the tube, on top of the shell.

(I didn't take any in-progress photos because I wanted no distractions of any kind!)

When it came time to braze the joint, I did a much slower preheat. I heated up the bottom of the shell first, then heated the tube well above the joint, then melted the flux, then slowly heated up my first quarter-section. This was the "trouble spot" from last time: the large area between the chainstays. Once everything was up to heat, the silver flowed extremely easily. As you can see in the photo above, this time I got it right: full penetration all the way around.

(I forgot to mention in my post about reaming out my stranded tube that, except for the area where no silver flowed, the silver was perfectly even everywhere else. I've heard that silver can be a bit uneven—that you can think you got silver everywhere since it flowed from top to bottom, but in fact there are gaps in between. That wasn't the case last time, and I'm sure it was as even this time.)


I was a little less successful with my shorelines. They're a bit bubbly, and there is one miniscule gap on the non-driveside. But really, it's very good, and this isn't an area where I demand absolute perfection. If it was one of the headlugs or the seatlug, I'd go in and add some more silver and make the shorelines perfect. In this case, I'll leave it! (I do need to work on my tacking, however. I always cause a mess in that step. I have a fair amount of silver to file off the top of the lug...)

So "Adam Jr." is underway! I'm excited for the next step—cleaning up this joint, tapping and facing the shell, and then I guess tacking the rest of the front triangle...

6 comments:

Dan said...

Nice to see you building Adam. I'm working on another frame as well. I have to wait till I recieve some fillet pro from fred parr to finish the seat stay attachment but it's looking like a bike anyway. My shorelines are also not as nice as I would have liked but that's all in the practice. I built a fork a bit ago but I had a bad feeling about it. I used brass instead of silver for the steer tube but didn't get penetration. I ended up cutting it up a just to see and tossed out $100 for sport. Keep practicing and keep up the building.

AH said...

Hey Dan!

So when you cut it up, how was the penetration? If the $100 was thrown away for sport, it must have been pretty good :)

Cutting that tube out of the BB was a pain, but at least I got to reuse my BB and not entirely waste a tube. I'm really happy it worked the second time around.

Unfortunately I need taps/facers before I can proceed to the next step -- more money!

XO-1.ORG said...

I am really enjoying following your frame-building career. Let me know when you're ready to accept my order!

AH said...

Thanks, Chris -- I most certainly will let you know!

Dan said...

Penetration was poor. The thickness of the tube and crown were big factors and i had trouble keeping the heat up all the way through without over cooking it. Brass was a poor choice with these parts. too thick and not a loose enough fit but I wanted to try anyway. Silver would have worked much better and I've done a couple more that worked fine with silver.

OAP said...

Dan, I feel your pain. Plenty of botched crowns and BBs on my end by trying brass. I'm getting there, I hope!