Lug/BB Reshaping (changing angles)

[Dazza]

Yes, I'm already thinking I'll do the HT lugs in bronze. I have a combination of a lowish BB and slightly taller fork for bigger tyres and fenders. I'm at around 59 deg for the DT/HT lug with the 72.5 HA. Lug is 60 deg and it won't sit well without a bit of new shape set into it.

for a degree or two, a die grinder with burr and then drums will ease the fit without the need to distort the lugs
and silver will be fine, using the flame with finesse to fill the internals.

[devlin]

I ended up doing that last night. I sat for a long time sitting up close to the joint looking at what I was trying to achieve and the real movement of the tube and lug. Studied where I needed to relieve the inside to give me the space to achieve the geometry I was after. I now have it sitting nicely with out any pressure anywhere to hit my numbers.

[Mtblucas]

The chain stay sockets can be bent a bunch.

I just finished a front triangle and am working on the chainstays. Even after working on the CS sockets with a rotary tool they are still off by a degree or two. I'm a little worried about hollowing them too much. I am trying to decide if I want to bend them and am wondering if the chainstays themselves are strong enough to do the work. I'd assume oval chainstays would be plenty strong enough to not kink under pressure but I didn't want to risk it without seeing what y'all think first. Thanks!



Matt Lucas

[Eric Estlund]

Singing tubes as a lever isn't a great idea. At least not the ones you intend to use.

[Mtblucas]

Thanks Eric. I realized, like an idiot, that I cut the CS’s too short so I decided to use them to bend the CS sockets. It worked great, the angles are spot on now! I took a hammer to the BB to close up the CS sockets as best I could. I found it fairly difficult to do this since the BB is a difficult shape, and I hope my gaps aren’t too large. If the chain stays have a fair amount of play will the joint be adequately strong or do I need to take the hammer to it again? To a newbie it sure feels awful smacking the frame (BB) with a hammer but I guess it’s just what it takes. When doing this is there any chance to create cracks in the ST or DT brazes?

[Doug Fattic]

...I took a hammer to the BB to close up the CS sockets as best I could. I found it fairly difficult to do this since the BB is a difficult shape, and I hope my gaps aren’t too large. If the chain stays have a fair amount of play will the joint be adequately strong or do I need to take the hammer to it again? To a newbie it sure feels awful smacking the frame (BB) with a hammer but I guess it’s just what it takes. When doing this is there any chance to create cracks in the ST or DT brazes?

Matt, I don't hit the shell sockets directly with a hammer, but rather use a punch between the hammer and the shell to more precisely place the blows. I especially what to close any gaps at the end of the socket to make it easier to get clean shorelines when brazing.

[Mtblucas]

Thanks Doug, I was very careful when using the hammer and only used it on the outside area of the sockets. I used a punch on the inner areas. I lit a flashlight inside the B.B. and sighted down the stays. The gap doesn’t seem super wide so I think they should be ok for a strong braze. I also worked a little more on the shoreline area and it’s looking good to me now. I appreciate the help!

[timto]

I recently saw this pic on the web and thought to add to this thread for thoughts. Not the first time I've seen this operation done. Thoughts? Not BB specific I realize but relevant to lug angle changes I think!.

[Mtblucas]

Wow. That’s the first I’ve seen that. I’m not an expert but it seems you’d lose a lot of strength in the joint that way no?

On the other hand, there is a large intact section in the lug between the two cuts so maybe with a tight miter it’d be ok.

I don’t know, ignore me. I’m only on frame 2 :)

[Andrew R Stewart]

If the tubes are in contact and the filler is flowed to this contact joint then the lug's additional material is icing on the cake. Think of a non lugged frame being strong enough. Andy