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How to examine test brazed lug practice?

Old 11-21-21, 07:11 PM
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Tandem Tom
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How to examine test brazed lug practice?

So get back to using the torch I am making up samples to simulate lugs and tube and silver brazing them. So I want to evaluate the penetration of silver through the joint. My first attempt today I cut the lug into quarters and looked at each quadrant to see the results. One was lacking.
So am I on the right track for evaluating my test pieces? Or is it enough to just see silver at the opposite side?
Thanks!
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Old 11-21-21, 07:25 PM
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Section enough samples so that you are confident that by looking only at the exit edge of the sleeve and seeing silver there you know that there's silver everywhere with in the sleeve's joint. Another way to monitor the flow through the sleeve is to drill small (like a stay's vent hole) holes at certain positions. Of course this is not what is done with the real jug/frame Andy
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Old 11-21-21, 08:06 PM
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Thanks Andy! I will give that a try. I am pinning the test joints. I think this was your idea I came across in reading old posts.
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Old 11-21-21, 09:12 PM
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I generally us pins to locate the sleeve, keep it from sliding down the tube it's around. I find it easier to braze a test sleeve with the tube vertical and have gravity aid the filler flow.

For the actual frame lug joining pins are for me more about holding dimensions and rotational relationships during the mitering/fit up step.

But pins also can act as a filler penetration "window". I will sometimes grind a flat along the pin to further aid the filler's flow along the pin's contact with the lug and tube. Andy
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Old 11-21-21, 10:51 PM
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Tom, the purpose of brazing practice is so you can learn to coordinate your hands working together as a unit. You probably haven't brazed in awhile so it is normal that the habits you learned in class are now a bit rusty. Perhaps you are using a short section of .058" slip tube over another tube? As you remember, it is common that a beginner moves the torch hand while the other hand holding the silver freezes when the joint is hot enough to add the silver. Or when adding the silver your torch hand doesn't move and you overheat a spot. With practice, muscle memory allows both hands to be operating together at the same time (without having to pay attention to both at the same time). You will eventually know your silver has covered the entire area you are heating because your heating pattern covered the area evenly. A common rookie mistake is that their flame pattern is inconsistent and does not paint the area evenly. It goes over some parts too many times while avoiding others. In beginning practice, I wouldn't worry too much if every mm is covered with silver. Like I said, your primary purpose is to be train your hands to work together. Eventually it becomes instinctive they are coordinated.,
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Old 11-22-21, 07:55 AM
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My experience level is far below that of a pro so I error on the side of adding too much filler as opposed to too little. You will know that the joint is full when you can't pull filler on the edge of the lug inside anymore, or doing so causes filler to escape somewhere else. After filling the joint, if there is some extra filler hanging out on the lug line, a stainless steel brush can be used to swipe it away. Just make sure the floor of your shop has a safe landing zone! I read on the framebuilders list one time that Brian Baylis said he used a piece of braded wick to suck away extra filler on the lug line. I think he referenced stainless steel wick. I'd love to know what exact product he used...
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Old 11-22-21, 09:25 AM
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IIRC BB used common non SS brake cable inner wires. I've tried this method to suck off excess filler (silver) but never got comfy with it so I just filed away the excess. Andy
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Old 11-22-21, 10:06 AM
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I don't do this very often, but I have used a piece of cable I found on the floor of my garage to get rid of excess filler. I imagine as long as it's not coated it will be okay. Use flux and don't overheat.
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Old 11-23-21, 09:11 AM
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Originally Posted by Nessism View Post
My experience level is far below that of a pro so I error on the side of adding too much filler as opposed to too little. You will know that the joint is full when you can't pull filler on the edge of the lug inside anymore, or doing so causes filler to escape somewhere else. After filling the joint, if there is some extra filler hanging out on the lug line, a stainless steel brush can be used to swipe it away. Just make sure the floor of your shop has a safe landing zone! I read on the framebuilders list one time that Brian Baylis said he used a piece of braded wick to suck away extra filler on the lug line. I think he referenced stainless steel wick. I'd love to know what exact product he used...
i believe proper lug brazing techniques makes removing excess silver right along the shoreline unnecessary. Clean shorelines start by making sure the lug (or shell or crown) fits tight against the tube. My punch set is heavily used before flux is applied. A punch allows you to direct your hammer blow precisely where you want it to hit the socket. If you leave even a little gap, it is an invitation for silver to either bulge or shrink inside at that location. Another technique I use to get clean shorelines is to leave extra head tube and seat tube sticking out beyond the lugs. This way you can draw any extra silver out onto this surplus tubing. Otherwise it is almost impossible to get the exact amount of silver so there is neither a gap or bulge. Besides that extra length of tubing is useful for alignment checking.

How to move the torch over the shorelines (tip size, speed, angle and distance of the flame, etc) to clean them of any extra silver (or find gaps) is one of the hardest things for my students to catch on how to do. It is somewhat complicated to explain but essentially you move the flame at the speed the silver along the shoreline can melt and then you dump it somewhere. In my framebuilding class manual (which thankfully has never been leaked on the web yet), I write more than a page on how to do this.

The 2nd most common rookie mistake is to apply too little silver while heating too long (or too much). The rule is that if there is no extra silver on the shoreline, you either add more silver or stop heating. There is no 3rd option. Beginners like to go over the area again with their flame even after they see silver peeking out at the destination. There is no reason to cook the joint (a very common tendency). Part of the reason for this common mistake is probably insecurity wanting to make sure the silver is everywhere inside the socket. And wanting to repeat there success not realizing more heat than necessary is causing more damage than making an improvement.
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Old 11-23-21, 11:56 AM
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Originally Posted by Doug Fattic View Post
Clean shorelines start by making sure the lug (or shell or crown) fits tight against the tube. My punch set is heavily used before flux is applied. A punch allows you to direct your hammer blow precisely where you want it to hit the socket. If you leave even a little gap, it is an invitation for silver to either bulge or shrink inside at that location.
Hi Doug,

Can you describe your process for closing down lug gaps using a hammer and punch? I've seen videos and the guys often do this after heating, while the lugs are mailable. How to see gaps when the lugs are slathered with flux though? Anyway, any help appreciated.
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Old 11-23-21, 12:14 PM
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Originally Posted by Doug Fattic View Post
i believe proper lug brazing techniques makes removing excess silver right along the shoreline unnecessary.
I agree with you except when my cataracts got really bad I couldn't tell if I had overflowed the lugs or not. I haven't built another frame since I got surgery, hopefully it's better now.
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Old 11-23-21, 01:32 PM
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Originally Posted by Nessism View Post
Hi Doug,

Can you describe your process for closing down lug gaps using a hammer and punch? I've seen videos and the guys often do this after heating, while the lugs are mailable. How to see gaps when the lugs are slathered with flux though? Anyway, any help appreciated.
Sure, the goal is to curve the edge of the socket in until it touches the tube. There may still be some small empty space between the socket and the tube behind it. This removes the opportunity for silver to puddle in the space between the lug and tube on the shoreline. So I'm punching the socket wall at a bit of an angle. In other words the end of my punch is not parallel (with the handle being at exactly at a right angle) to the tube (like one might think) but rather at a bit of an angle to the tube. This is done long before I start to flux up the frame for brazing. In fact I have only the one lug and two tubes in my fixture when I do this. I do this only one lug and two tubes for each joint separately. Before I get to that point there may be some more major blacksmithing in grinding or using solid bars for altering angles.

When I was learning to build frames with brass in England in 1975, we kept a small a small hammer for smashing lugs into submission while we were brazing them up. Stamped and welded lugs in that era were pretty crude. They were better pre and post WWII but there was a decline in bicycle usage and as a result quality slipped. I seldom use a hammer now while brazing although I do have a small brass one handy in case i need to close a gap in the middle of brazing. I try to carefully get everything to fit up nicely before lighting the torch. This is part of the reason I almost never have to use a file to get rid of excess silver.
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