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Fiveflat 02-27-14 10:13 AM

Ugh... Lesson learned
 
1 Attachment(s)
I've always had a passion for bike frames and I have a long history of metal work and fabrication. I *thought* I knew what I was doing BEFORE I did research on bike frames and particularly lugged frames. I think I can still pull it off and make the best of this but here you have it, I'm opening myself up to ridicule, laughter, insults, all the rest.

I'm the last person to brag on myself, but I can really stack some dimes with my welder. Brazing is definitely something I need a LOT more practice with and I must move to silver solder.

http://bikeforums.net/attachment.php...hmentid=366287

Cynikal 02-27-14 04:50 PM

Not a bad start. Have you brazed before? I would start with tight fitting tubes so you can cut them up to verify penetration. I’m just starting to learn brazing myself and I’m local to you. Let me know if you want to connect and chat bike/welding stuff.

unterhausen 02-27-14 05:53 PM

So that's bronze?
the bb shell has the advantage that you can tell if you got penetration by looking inside. What does it look like in there? Unfortunately, it looks like there wasn't quite enough heat to get good penetration. OTOH, it's not burned to a crisp, although you overheated a spot up the seat tube a little.

I'm always a little surprised that people don't practice on pieces of tubing. When I'm doing something new I practice with tubing and I've been brazing since the mid-'70s. .058 inch wall tubing is a decent slip fit over the next 1/8" smaller diameter tubing. So much cheaper than parts.

JohnDThompson 02-27-14 06:15 PM

The build up of brass on the tubes suggests that you didn't heat the shell enough before starting to add the brass. The thin tubing heats much faster than the thick shell, so the brass will tend to pool out on the tube before going into the joint. Keep the flame on the shell until it's fully hot before hitting the flame on the tube. That way when the brass melts, it gets pulled into the joint right away without so much pooling. This was right after washing off the flux, before any finishing:

http://www.os2.dhs.org/~john/paul/track0008.jpeg

Andrew R Stewart 02-27-14 08:56 PM

I'd suggest that you consider getting more comfy with bronze before trying silver. Why? because you need to get better with something, bronze is FAR lower cost, it's stronger if the gaps are large of the joint is less then well cleaned, You'll want to use it for some joints even if you are silvering all that you can and more reasons. I find it harder to flow braze with brass because of the higher temp, when i go to silver there still is a remembering curve but less then th other way around IME. I second Eric's advice of tube sleeves as practice. i have 4 cut and ready for prepping in a box I'm taking to a friend for when i help him paint my recent frame. He's also going to give me a brazing tune up. Andy.

Fiveflat 02-28-14 09:34 AM

Quote:

Originally Posted by Cynikal (Post 16533304)
Not a bad start. Have you brazed before? I would start with tight fitting tubes so you can cut them up to verify penetration. I’m just starting to learn brazing myself and I’m local to you. Let me know if you want to connect and chat bike/welding stuff.

Yea, that would work. I'm actually a little south of Sac but not far. Always got a good selection of cheap beer in my shop fridge too ;)

Fiveflat 02-28-14 09:38 AM

Quote:

Originally Posted by JohnDThompson (Post 16533492)
The build up of brass on the tubes suggests that you didn't heat the shell enough before starting to add the brass.

Exactly, I figured this out by now. I think I'll have much better luck with the rest of the joints. I did get good penetration into the shell of the BB but it's just not the prettiest from the outside.



Thanks for all the constructive criticism from everyone, rather than bashing. I appreciate the help and will try to apply all the suggestions here!

unterhausen 02-28-14 12:54 PM

I always used silver for lugs, and the fact that I hadn't used brass grated on my nerves a little. The first lug I did with brass, I didn't get full penetration and the filler refused to budge for me after a while. So I cut up some tubes and practiced on them. I made sleeves of 1/2", 1", 1.5" and 3". The smaller ones went fine, but with the bigger sleeves what I found was that my torch wasn't supplying enough heat. After a few tries, I could flow brass through a 3" sleeve, but it was all I could do to keep it hot enough to make that work. That exercise was really useful to me. I got the biggest tip my tanks can handle and it went a lot easier.

neurocop 03-09-14 01:35 AM

Quote:

Originally Posted by unterhausen (Post 16535880)
I always used silver for lugs, and the fact that I hadn't used brass grated on my nerves a little. The first lug I did with brass, I didn't get full penetration and the filler refused to budge for me after a while. So I cut up some tubes and practiced on them. I made sleeves of 1/2", 1", 1.5" and 3". The smaller ones went fine, but with the bigger sleeves what I found was that my torch wasn't supplying enough heat. After a few tries, I could flow brass through a 3" sleeve, but it was all I could do to keep it hot enough to make that work. That exercise was really useful to me. I got the biggest tip my tanks can handle and it went a lot easier.

FWIW I also prefer silver to brass for lugs and for any sleeved joint that is relatively tight-fitting, because silver rod: 1) melts at a lower temperature;
and, 2) is more easily drawn by capillary action into the joint. Brass may be stronger for looser fitting joints.

unterhausen 03-10-14 04:49 PM

I thought it was interesting that the people that learned on brass said it was easier than silver. Now that I have a properly sized torch tip, I am not sure I agree, but there isn't much difference.

tuz 03-11-14 10:17 AM

My experience is that brass flows quite well in lugs with the right amount of heat. I like that the flux is quite tolerant so you can blast the joint and braze rapidly. 55+ % silver does flow very quickly but you have to be a bit more gentle with the flux. 50% (and under) flows more like brass.

fietsbob 03-11-14 02:18 PM

kind of a +1 ... heavier castings like fork crowns and bb shells
focus on heating them first and the tubes will likely be hot enough .

playing the flame on them later and little ..

another + on tight fits .. silver wont fill the gaps that brass will .


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