Here is my first attempt at a fillet brazed joint on anything other than rack tubing (read: bike frame sized).
Joint fluxed:
Joint tacked:
Tinning pass:
Building the fillet:
Smoothing out the fillet:
Soaked and cleaned up:
Feedback appreciated! Tell me what looks good and bad. 
Thanks!
-Jim G
My input. Skip the tinning stage. You donât really need to do that. The purpose of tinning is to make sure youâre getting an internal fillet. Done properly, a brazed joint will achieve an internal fillet in a single pass. I did lots of testing of this in the past by cutting up test joints. There was no real difference internally between a tinned joint and a normal joint. If you really feel you should tin the joint, then the example youâve shown has way too much filler. You want to get the whole joint up to temp and get in and out of there fast. You should see a little bit of filler on the outside but hardly any. As I said, get the joint up to temp, add filler and as it sucks into the joint keep moving. Whole joint like that should take about 30 secs for tinning. You should be left with a thin brass line round the joint.
Iâm also not convinced by a separate smoothing/shaping pass, I know Tom Ritchey does it but unless you can get a no-file joint done that way, youâre going to be filing it anyway.
One thing to remember is that heat is the enemy of the material. The higher the temps you get it to and just as importantly (if not more) the number of heat cycles you put into that tube, the more damage youâre doing. Youâre also going to be making things difficult for yourself when it comes to alignment.
It looks to me is some of the pics that youâve not got the base material hot enough all over. You can see this from the hard transition of the braze onto the tube. This should be totally smooth with no ridge.
The pic below is a recent braze, toptube to headtube I think. Itâs a single pass, total time brazing that joint was maybe 3 or 4 minutes. You can see how the filler is flowing out onto the tube with no ridge or bump. You need to get everything up to temp for that to happen. That joint was probably run a little hot to be honest, you can see the copper separating out of the filler at the edges and a couple of spots of burnt flux (not all the black bits, thatâs just the way Cycle Design Flux looks).
Hope this helps a little. Keep posting pics and practice, practice practice.
Paul Brodie just posted a new video with additional fillet brazing techniques. It may be helpful.
Thanks to all for the helpful feedback!!!
Hereâs a second try. No tinning pass or smoothing pass this time, and I tried to make sure that the metal was hot before applying more brass. I think I got the edges to wet out better/smoother this timeâŚ?
Straight off the torch:
After soaking:
Thanks!
-Jim G
That looks way better. Good job. It looks a little like you go back and forward a little on the brazing? Thatâs what causes the uneven lumpiness on the flatter sections of the joint. I try to make sure Iâm not going back and remelting any of the filler. I braze a little like if I were tig welding, once I get everything up to temps Iâm adding filler and moving forward, add filler, move forward, Iâm not going backwards at any point. Iâll stop and reposition the tubes/frame maybe 5 or 6 times during a full braze. Just to make sure gravity is working for me and I donât have molten filler sloshing all over. Keep going and just practice as much as you can.
Hey Jim -
One quick tip for practicing⌠Rather than miter the longer tube to fit the stub, miter a bunch of stubs to fit the longer tube. And, if you want to make it a little easier on yourself, make the stubs out of a smaller diameter tube than the main tube, and miter them at something other than 90 degrees. Like this:
As with a lot of things, Iâve found that being comfortable and being able to change the position of the work easily while brazing is really important.
Finally, miter 4 or 5 at a time so you can work back-to-back-to-back without any pressure to get it right on the first rep⌠Regardless of how much practice one has, the 2nd or 3rd joint is always going to go better than the first.
Then just do a couple hundred joints and itâll start to click. Haha.
-Chris
Thanks. I rewatched the âHow To Bronze Brazeâ video where he talks about melting the leading edge of each âcoinâ when adding fillerâŚthatâs what I was going for this time, but it didnât work as cleanly as in this video. I should probably mention that the tubing Iâm using for practice is 1-1/8 x .100" and my torch is oxy-propane (Victor 2-TEN tip) â the tubing takes a relatively long time to heat up and I donât have the hot pinpoint flame one gets with oxy-acetylene, so once things get up to temp, the brass tends to flow everywhere. Is this making things harder for me than need be? Probably I need more practice to improve my heat control? I intend to keep trying!
Thanks â thatâs a good tip!
I braze with oxy / propane as well. I donât know the tip youâre specifying, but I tend to bust out my biggest Smith tip for main triangle fillets.
My settings are between 8-10 PSI on both gasses (always equal to each other) when doing main fillets, using a neutral flame.
I find the biggest difference between propane and acetylene is that you have to be more patient with propane. It just takes longer to heat stuff up, but patience is really important when brazing.
Hereâs my 2nd try cut in half. Doesnât look like Iâm getting any penetration inside the tubes. :(. Does this mean Iâm not getting things hot enough? Or is my joint too tight? OrâŚ?
Are you fluxing the tube before fitup or just pasting the flux round the joint after fitup?
Yes, Iâm fluxing before the fit-up.
Thatâs some beefy tubing. Have you tried thinner tubing yet to practice on like youâd be brazing on for frames?
Not yet â this is all Iâve been able to scrounge up to practice on.
-Jim G
Your second attempt was much better. 
I agree that using thinner tubing similar to what youâll eventually braze would be helpful. Youâll probably get better bronze penetration with the thin stuff without changing your method.
So hereâs my latest practice attempt, this time using .045â wall tubing. I think I got better internal penetration but worse heat control. My torch was either too hot or too cold, I couldnât find the happy middle.
Thanks for any feedback!
-Jim G
Some quick thoughts from a fellow newbie, so take them with a grain of salt. Iâd be interested to hear from the more experienced brazers as well.
I think of heat control as being a function of the following, in no particular order:
One final thought: If you start the joint with the goal of good internal penetration, you may be getting the workpiece hotter than necessary straight away and then spend the rest of the joint chasing your tail as you try to manage heat. Iâve been practicing on pieces of flat metal so that I get a good feel for how to achieve a properly wetted braze. This eliminates some of the variables/difficulty of brazing tube joints while Iâm still developing my feel for the process.
Hope that helps!
Thanks for sharing all that insight! Much of it makes total sense!
Tip Size â Iâm using oxy/propane with a UniWeld71 torch, a Victor UN-J elbow, and a 2-TEN tip. Propane pressure is about 5psi, I donât know what pressure my oxy-concentrator outputs, unfortunately.
Flame-to-joint distance and angle consistency â I am not doing a good job here. This comment totally made me go âDUHâ because I just finished up an introductory welding course where our teacher tried to drill this concept into meâŚand of course I forgot! Thereâs a big difference sitting at a welding table in a chair with good arm support and a flat plate vs. standing at a round joint clamped in a vise with your hands and arms waggling around in mid-air. I should know this!
Material thickness vs. heat â YUP. Because I was (over) focused on getting good penetration, I again attempted to tin the joint (even though Iâd previously been given the advice to NOT do that), which of course made everything hot when I tried to lay a fillet and the brass just ran everywhere. Paul Brodie uses a big flame to tin, and then dials that down to a very small flame to fillet â but heâs using acetylene which probably(?) works better this way. I was trying both bigger and smaller flame sizes, and the small one seemed like it just didnât have enough oomph to heat up the part â so I increased the gas/oxy to make a bigger flame, which then heated things up broadly and made the brass run all over. I need to practice more patience here.
Work holding â I did have the joint clamped loosely in tubing blocks held in my bench vise, and I was trying to rotate things around so I was mostly working flat.
I did previously tell myself to practice on some flat bar, but I got impatient and went straight for another practice joint. Again Iâm reminded of my welding class because ALL WE DID was lay beads on flat plate! Iâll try that next.
Thanks!!!
-Jim G
