It's a bit weird that the carbonization occurs right around the fillet. It might be an indication of a too small tip (i.e. not enough heat but too high temp.). What size tip, type of fuel gas & flux are you using?

I'm using a Meco Aviator jet with #5 tip. The flux is stay silv (white paste) and I'm using oxy acet. I have been trying to do the flick thing as much as possible but it still makes it hard to melt the filler.

I'm also noticing that I am not getting as much penetration as I would like.

That's what I thought... looked like silver flux. You are using flux for silver brazing. You need the proper flux!

According to the tip chart, #5 meco is a 0.0635" orifice. I'm not very familiar with acetylene, but a number 2.5 or 3 might be better.

tuz, good catch on the flux. Silver flux doesn't work with bronze no matter what my LWS counter person belligerently tries to argue. After that argument, I tried it on some scrap and it didn't go well. I'm amazed the joint looks as good as it does.

I'm pretty sure the #5 is too big, it's the same as a Smith AW208. I forget what the largest tip I have for my Smith, but I think my tanks will only flow enough acetylene to keep up with a AW207 and that is a huge tip. And I have always liked using a lot of heat. I'm pretty sure the biggest tip Doug Fattic recommends for acetylene is a Smith AW205, which is halfway between a Meco #2.5 and #3

Thanks guys for the feedback... I had to run to the LWS for a shop errand and picked up some black flux......Prior to reading the last 2 posts..

...And as what many have said, I have been taking the advice from the guys at my welding shop.

The black flux is also for silver. It has a higher temperature range but it is not suited for brass brazing.

Just read that =(
Lesson of the day, do not listen to the guys at my LWS on matters of brazing material.

If I may highjack this thread for a moment... I have lost the link to a table of tip sizes, by brand and model number. Would any of you out there have it? I believe that Alex ?. had posted it a few years ago. Thanks. Andy (Who wishes that the tip model numbers would directly indicate their orifice diameter).

here's the tip size chart I was consulting for my post above: LINK
The original is a little nicer, didn't find it right away (maybe I'm thinking of the excel spreadsheet you can d/l from that link)

I use an AW207 for brazing lugs using bronze, I found the 205 wasn't big enough to keep everything up to temp. AW205 is plenty big for everything else.

I did that long ago (sorry OP)

I think lowes might have borax flux powder for bronze which you can suffer with until you order some good stuff. The worst part about that is cleanup, it turns to glass after you braze and only really hot water takes it off, that or a hammer

It is always difficult to diagnose brazing problems from just a picture alone. Although in your case one can see you used the wrong flux. Even though it can be obvious the joint got too hot, more information is needed to know how it got hot, like was the flame too close? or were you too slow flicking the flame away? There are all kinds of possibilities. It really takes observation to figure out what is going wrong. I'm positive your tip is way too big for a beginner. A bigger the tip requires faster reactions. Most people starting need extra time to interpret the heat indicators and then think of how to move in response. Use a tip below .040" in diameter.


Your goal is to control the brass puddle by keeping it in between the liquid and solid state. Primarily you do this with a flicking motion (like unterhausen said) so just as the puddle takes the desired shape the flame is flicked off and then applied again as more brass is added. Like an on off switch.


Most welding stores sell brass granular flux in a yellow pint sized can. Or as least they used to. It is designed so that the rod can be heated up and then dunked into the can so some flux will stick to the end of the rod. Some can be taken out and smashed up a bit and made into a paste by adding water. This brass flux is nowhere near as good as Gasflux type B or the stuff from Cycle Design. Get the right brass too. Its like wanting to learn to cross country ski with down hill skis. It doesn't work and one doesn't learn using the wrong tools.

I'm going to be buying some stuff from cycle design here shortly. As far as the brass I'm using, it is LFB from pinnacle alloys I purchased from my LWS. I'll also move to a smaller tip via the comment above. As far as in the meantime (until my cycledesign flux arrives) I can play with borax.

Thanks again for all the help and comments, I really appreciate it!

I haven't tried either Gasflux or Cycle Designs stuff. Maybe I don't know what I'm missing but I get along very well using what I am. I'm getting Petersons flux (No1 Blue) and off the shelf bronze from the LWS. Can't relate to the torch and tip sizes. I currently use a Smith medium duty (CW5A). The tip sizes are different from the light duty shown in the chart. I'm using an MW201 and MW205, which I believe relate to AW205 and 207 respectively.

With the "blue" flux I use it both powdered and paste. Throw a little powder in a jar- add a little water- screw the lid on tight and in the morning you have paste.

One factor that contributes to my success (I believe) is cleaning the rod. I sand all the coating off and pull it through an acetone rag. Nice clean fillets with no pinholes. The flux comes off in "very" hot water. Very little cleanup. I don't know the brand of filler, but it probably helps that the LWS supplies a big share of framebuilders here in PDX, and they are very knowledgeable and helpful.

If a pic is worth a thousand words a vid is worth a thousand pics(well maybe not a thou!) That would be great to see from a helmet cam view. Here's a vid of one builder's technique: https://www.youtube.com/watch?v=YFCdsX1j_u8

"I shouldn't tell you this, but my goal is to produce a fillet that doesn't need filing"

On the contrary, it seems that would be the ultimate goal of a fillet braze. Doug Curtis (Curtlo Cycles) does his fillet brazed frames without filing. I have two of his frames, they look great to me.

This is a great thread, thanks to all for your input.

Brian

Steve Garro also produces frames without filing and sells them at a discount. That's where I got the idea. I remember slaving over my tandem for hours on end and it still isn't perfect because I wanted to ride it. The main thing that drives me crazy is the little ridge at the edge of the fillet, takes forever to get rid of that because of the danger of undercutting the tube.

^ Some of Steve Garro's unfiled fillets from his blog to give us novices/newbies something to aspire towards https://coconinocycles.blogspot.com/






.......and the finished filed fillet. According to his site he sells the unfiled frame for $200 less than than the filed. Interesting how he flows the st and seat stay fillets together, I suppose because the od of the st too small to practically keep them separate(or does it add any significant strength?).

That video was cool, it's always interesting to see how others do these things. Looks like he lays down the brass and then smooths it with the flame ( time consuming, like he says in the vid) where in contrast Garro's unfiled fillets are just as they came when the brass hit the steel...making the brazing go twice as fast as the video.

I want to emphasize a beginner can make a really nice fillet brazed joint right away if they get the right instruction. I always hesitate to press this point because it sounds like shameless self promotion but it is also true. To illustrate my point I'm posting a picture of 5 fillet brazed joints that were the very first ones done by students. They all have different natural abilities so there is of course some quality differences among them but it should be obvious they are all satisfactory and with more practice will get better. There was no particular selection process for which ones I choose except what was on top of the scrap bin.


Of course these aren't the first brazed joints of any kind these students have done. I start with the simplest thing they can do with silver just to get a feel for the torch and keep adding complexity until the are ready to do a fillet joint. Background to this point includes selecting the right equipment and materials. In addition there is general instruction on the principles of brazing but then very specific details of each motion at every phase. If a student wants to be really good they will commit this information to memory so their concentration can focus entirely on hand motion. Now a foundation has been laid so a demonstration can illustrate exactly the points already learned. I also want to add that a good instructor knows common beginner mistakes and how to avoid them.


Also don't underestimate the power of a really good teacher. They are able to not only provide info clearly with economy but also understand the psychology of each student. You can't remove the emotional reaction to the process. Students learn in very different ways and a good teacher can adjust to these variations. My point is that if one wants to be really good they start with really good instruction from a master. There can be other routes to success but this one is for sure going to get you the farthest the fastest.

interesting that he seems to be heat sinking the head tube. Most people say that causes more issues than it helps

Doug, thanks for posting that. The two examples in the upper right are pretty impressive. Shameless self-promotion is acceptable in your case

I have a question regarding the brazing sequence of this lug, which I presume is made from a larger ID "sliding fit" tube on the st. Once the lug is brazed to the st wouldn't heating to join the stays and tt make the lug brazing material flow again? Or is the lug brazed to the st second in sequence and silver used?

thanks, Brian

Pretty sure he sleeves first. Silver isn't going to re-flow at brass temps in that situation. If it does, there is nothing to make it move from the shoreline, so it will just re-solidify.

Doug Fattic:

"I want to emphasize a beginner can make a really nice fillet brazed joint right away if they get the right instruction. I always hesitate to press this point because it sounds like shameless self promotion but it is also true...

Also don't underestimate the power of a really good teacher. They are able to not only provide info clearly with economy but also understand the psychology of each student. You can't remove the emotional reaction to the process. Students learn in very different ways and a good teacher can adjust to these variations. My point is that if one wants to be really good they start with really good instruction from a master. There can be other routes to success but this one is for sure going to get you the farthest the fastest."

Couldn't agree more with Doug. The thoughts Doug has written above are not just his opinion but are factual backed up by decades of learning theory reseach and documentation with thousands of books and dissertations written on the subject of how people, and animals, learn(google learning theory). I've been a credentialed(CA) elementary school teacher and a glass blowing instructor at a community college and while certainly not viewing myself as a master of either cannot emphasize enough the importance of a knowledgeable teacher/instructor meeting and understanding the students individual needs and abilities.

unterhausen:

Pretty sure he sleeves first. Silver isn't going to re-flow at brass temps in that situation. If it does, there is nothing to make it move from the shoreline, so it will just re-solidify

Made sense as soon as I read it, thanks.

Brian

Oh my goodness... It is amazing what using the correct flux and tip makes.....my clean up job just became a lot easier.

just out of curiosity, what did you end up using?