Lug brazing with brass. Need some help.

So what is the trick to pulling the braze material all the way through the lug? I am having a real tough time getting that to happen. I realize it's not an easy task, but I think there is something I'm missing. So far, I'm a master at getting the brass at the top of the joint, but never see any being pulled through to the bottom. The material seems to end up running down the outside of the lug rather than through the inside. Is the sleeve too tight? I seem to be much better at fillet brazing that lug brazing.
I think my heat is adequate and I'm trying to heat up the all around the brass to get it to flow where I want; but nada.
Any tips you might be able to offer? I could use some.
Thanks in advance.

Without see your work or you brazing we can't be specific but here's some tips.

The lug's fit on the tube needs to be looser then with silver. I judge by holding the tube vertical and then slip the lug onto the tube. It will slide down the tube pretty much on it's own with very little tapping of the tube's end on your bench top, for silver the lug will slide a little bit but need tapping to get it to slide a tad more.

The tube must be hot enough for the bronze to flow and wet out quickly. I find that most of my flowing bronze into a lug/sleeve problems are from poor/uneven heat up. For bronze to flow the temp does need to be higher then when filleting or tinning. If you've seen vids of bronze lug brazing by experienced guys look at the color/temp of the joint, it's way hot. Of course watch your flux for overheating. I assume you do clean and flux the insides of the lug.

I place my rod on the tube a little bit above the lug's edge and work the bronze down the tube to the lug.

One trick I found to better maintain the temp level is to reduce the chimney effect a hot tube can have when it's ends are wide open. I'll plug one end with a cap or wad of AL foil wedged in. Andy

As Andrew mentioned you will need a looser fit with brass than with silver. I find most beginners focus heat in too small of an area and use too small of a torch. You need to have a relatively large area up to brazing temp to get the filler to flow through the joint. If you don't do that the filler has no where to go but over the edge of the lug. And with brass the joint needs to be red hot literally. There is a good youtube video of Brent Steelman brass brazing a fork. Big hot flame, "big ass tip", in and out fast. Check it out max fork brazing - YouTube

And this might sound stupid, but make sure you didn't get your hands on some stainless lugs by mistake.
I don't want to come across as preachy, but I'm of the opinion that one of the best thing you can do to become a better brazer is get proficient with brass before silver.

Quote:

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Originally Posted by Martin T

I don't want to come across as preachy, but I'm of the opinion that one of the best thing you can do to become a better brazer is get proficient with brass before silver.

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An absolute AMEN to that.

And this might sound stupid, but make sure you didn't get your hands on some stainless lugs by mistake.
I don't want to come across as preachy, but I'm of the opinion that one of the best thing you can do to become a better brazer is get proficient with brass before silver.[/QUOTE]

I went through this mistake earlier this Fall. I had bought a tube "set" a few years ago from a building community member and finally got around to using it. I discovered that the seat tube wasn't liking the bronze brazing to the Bb shell. Something made me think of SS and a magnetic and spark test later I decided it was SS. Interesting that the bronze actually wetted out on some of the SS tube, but not all. The cut off tube/shell now is a paper weight.

A bunch of years ago I decided to use bronze whenever I could. I don't do this frequently enough to be really proficient but do find going back to silver (mostly for braze ons) to be easy. Not that this is my standard but I'd rather trust a poorly done bronze joint then a badly done silver one. Andy

Thank you guys. After reading through your replies, maybe I'm not getting enough heat to more of the part. The lugs are practice stamped steel, and I think that it part of the problem as well since the fitment is pretty tight. I'm using a #4 tip and what I thought was a pretty big flame, but maybe not enough. I'll give it another go with something a bit larger and see if that helps.

Yes, I'm using bronze exclusively right now until I get good with it.

There are a few ways to open up a lug. Grinding the ID is one and what you'll want to do as a cleaning prep anyways. I have a 1/4" die grinder (a Makita) hose clamped to a wood block (with a relief to nestle the grinder) and then clamp the block I'm my vice. I've seen people ream the socket but that seems to work better on crowns and shells. Some will pry the socket larger, if you are changing the lug angle this will likely be the way. I've even heard of people using a hammer to beat the OD and stretch the ID a bit. You really want a easy sliding fit with no snugness.

My next frames will use two torches in a few joints. Andy

So after a few adjustments, like more heat and better sleeve fitment, I got it and it did what it's supposed to. I like it!


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