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  1. #1
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    A few questions about Fillet Brazing

    I want to construct a steel road bike frame in the future, and I want to braze it. I have no experience with brazing, but I have time, patience, and some money to spend. I plan on fillet brazing my frame for two reasons: it just looks sexy, and it seems easier and cheaper to practice than lugged brazing. Not that it is easier to do than lugged brazing, just easier to practice since one doesn't have to buy a bunch of practice lugs and stick to certain geometries.

    Anyways, I plan on buying some steel tubing and some brass filler rod, and start mitering tubes and brazing them into fun and interesting geometrical shapes. My questions for you gentlemen (and women) follow thusly:

    In regards to the tubing:
    I plan on getting a variety of diameters of steel tubing. Is there a right or wrong kind of steel tubing? What is a good wall thickness to approximate a bike tube? Basically, what should I be looking for when i go to the metal shop to purchase practice tubing?

    In regards to the filler metal:
    I looked around and couldn't find any SPECIFIC recommendations for filler metal. What exactly should I look for in brass filler? Any good brands, or does it even matter? I know the filler is made for specific applications, and I don't want to waste a lot of money on something that I don't need. I hope wherever I purchase the stuff there will be a knowledgeable salesman, but I would like to have a grasp on what I need before I get to that point.

    In regards to the brazing process:
    I found a few decent guides to the brazing process, this being the best: http://www.bikewebsite.com/weldbraze.htm (the fillet brazing instructions are at the bottom). I think I have enough of an idea of how the process works to start practicing it, but I have a few questions that would save me some time if anyone could answer them. How much does gravity affect the braze, meaning if I am brazing two tubes together, do I have to rotate them as I go along the joint so that gravity is always pulling the metal into the join? Or do the metals stick together enough that rotation isn't necessary?

    I would love to take a class on fillet brazing alone, but I am having a hard time finding any in my area. Where should I look? I don't know of any bike frame builders located in Atlanta I could learn from, but I would love to even just watch somebody do it. Are there any other trades that fillet braze tubing? Even if it isn't for bikes specifically I'm sure I could learn something.

  2. #2
    Decrepit Member Scooper's Avatar
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    Tim Paterek has a four disc set of "how to" DVDs on fillet brazing (lugless framebuilding). You can order them HERE.

    The Paterek Manual for Bicycle Framebuilders is an excellent "how to" book, and is available HERE.
    - Stan

  3. #3
    Andrew R Stewart Andrew R Stewart's Avatar
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    I like to use filler and flux by GasFlux, you can order then from http://www.henryjames.com/

    The type of steel, for practice, is not a big issue excepting it's dimensions and ability to be cut and mitered. 4130 is popular, any left overs can always be used for actual projects... Straight gauge tubing is available from a number of industrial sources. Bikes usually use .028" to .049" walled stuff. If you get a tube with .058" walls that's .125" larger in diameter then another tube it will slip over the smaller tube and have just about the right fit for lug like practice.

    Are there any sculpture classes in town? How about race car building? The only guy i know of in your area is not a full time builder. Andy.

  4. #4
    Senior Member Cassave's Avatar
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    Fillet brazing is often referred to as Braze Welding since the filler is maintained just above the solidus temperature, allowing buildup of the fillet.

    Tubing - Just buy low carbon, seamed and welded tube to start. 0.028 to .035 wall. AISI 1010, 1018, 1020 DOM, whatever you can find.

    Filler - Any filler that meets the AWS specs. I'd start with RBCuZn-A, -C or -F. I'd get both 3/32" and 1/8" rod.
    Flux - Get AWS Type 4 paste and powder fluxes. Paint the joint with paste, coat the filler rod with powder to start, fine tune to your preference later.

  5. #5
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    Quote Originally Posted by Cassave View Post
    Fillet brazing is often referred to as Braze Welding since the filler is maintained just above the solidus temperature, allowing buildup of the fillet.

    Tubing - Just buy low carbon, seamed and welded tube to start. 0.028 to .035 wall. AISI 1010, 1018, 1020 DOM, whatever you can find.

    Filler - Any filler that meets the AWS specs. I'd start with RBCuZn-A, -C or -F. I'd get both 3/32" and 1/8" rod.
    Flux - Get AWS Type 4 paste and powder fluxes. Paint the joint with paste, coat the filler rod with powder to start, fine tune to your preference later.
    Excellent information, thank you so much. Would a local hardware store sell filler and flux? Might there be a specialty store that does? I would love it if there was a brick-and-mortar place for me to go to. Nothing like a knowledgeable salesperson to help clarify some confusing numbers and letters.

    Quote Originally Posted by Andrew R Stewart View Post
    The only guy i know of in your area is not a full time builder. Andy.
    Might this person be willing to be paid for some one-on-one instruction? If you know him personally I'd love a referral
    Last edited by TickTockToe; 01-13-13 at 05:52 PM.

  6. #6
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    I would use 4130, how do you plan to hold the pieces square while everything is fitted and brazed? I ask because we build airplane fuselages out of 4130 tubing, and fitting all the tubes together and holding them in place is an involved process. You might want to find someone who knows how to braze and let them teach you, I would hate to see something on your frame break and you get hurt. I'm not trying to discourage you, but make sure for your own sake you know what you are doing,.

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    It sounds as if, from the nature of your questions, that you have little/no experience with "gas welding?"

    There should be a community college class locally dealing with welding, and specifically O/A. Never mind that it may not deal solely with "brazing." You have a bit to learn about heat control, torch control, and get the practice co-ordinating both hands, not to mention becoming familiar with the equipment.

    I read the text in the link you provided. I wouldn't read any further until you get some hands-on. In fact I'd disregard that altogether. There's more than a few inaccuracies, and it may confuse the beginner. Whether it was the authors intrepretation of the subject, or he just plain didn't know I'm not sure. On the subject of Paterek- many feel this is not the best resource, me included. You might get something out of it if you have some experience, but there are better resources.

    Over at the frame builders collective, Dave Kirk has a thread on "fillet brazing." Not a tutorial as such, but a good example of some excellent work. Again- you need some experience.

    Supplies will be available from a welding supply house. Yellow Pages lists a few. They have an Airgas store there. That would be a good place to start.

    Practice materials? At your level pretty much anything you can stick together. There's a lot to learn before attempting to stick bicycle tubing together. When you get to the point that you want to practice "bicycle joinery" use something approximating the tubing used in bisysle construction. I began wielding a torch (along with other weld methods) in dad's shop at maybe age 10. I'm about to turn 67 and been welding pretty much steady since. It was until about five years ago that I started f'brazing bicycle frames. I consider myself a pretty decent welder, and it wasn't like I needed to re-learn welding, but there are some considerations that are different. I wouldn't suggest anyone try to learn welding attempting to join bike frame tubes. You'll give both welding and bike building in a hurry..

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    if and when you decide to do this, I can send you some short scrap pieces of 4130, I can probably fill up one of those USPS boxes, the if it fits, it ships deal. We have barrels of the stuff. It would be good to practice on

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    Quote Originally Posted by reddog3 View Post
    On the subject of Paterek- many feel this is not the best resource, me included. You might get something out of it if you have some experience, but there are better resources.

    Over at the frame builders collective, Dave Kirk has a thread on "fillet brazing." Not a tutorial as such, but a good example of some excellent work. Again- you need some experience.

    Supplies will be available from a welding supply house. Yellow Pages lists a few. They have an Airgas store there. That would be a good place to start.
    other than getting Doug Fattic to teach you to braze, what are the better resources? The article at the frame builders collective was nice, but the site has been hijacked and I don't think it's coming back anytime soon. I learn a lot from people trying to explain things like that, it's too bad. My LWS doesn't have bronze-appropriate flux. They will swear to their last breath that something else will work. I would say that the counter person at the LWS only knows what their customers know, so they might be pretty good at GTAW, but very few people use bronze for anything anymore.

  10. #10
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    I suppose a bit off topic, but what are your thoughts on the flux coated rods? I have only used it on non bike related applications and it seemed to work well.

  11. #11
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    Or you can just ignore all the advice (including this) and just do it.

    I put my first frame together a week after buying the oxy acetylene equipment.

    I used stainless steel thin wall tubing, silver rods, non-standard geometry and a mixture of lugs and fillets, every one of which everyone says to avoid for your first frame. I did a few practice joints, they all worked so I just went for it. One howling cockup along the way, all part of the learning experience.
    Last edited by Mark Kelly; 01-14-13 at 02:45 PM.

  12. #12
    Andrew R Stewart Andrew R Stewart's Avatar
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    Quote Originally Posted by seankanary View Post
    I suppose a bit off topic, but what are your thoughts on the flux coated rods? I have only used it on non bike related applications and it seemed to work well.
    Flux coated rods are not bad but many don't use them for a few reasons. Will the filler you wish to use come in a flux coating? Is this flux easy to soak off in water? The base metal (tubes/lugs) still are getting heated and before the flux is introduced to this base metal there will be oxidation and such, with Silver this is especially bad.

    Most builders learn what fillers and flux they like (for whatever reasons) and some will dip their rods into that flux to add a little bit more flux when the rod is flowed onto the base metal. Andy.

  13. #13
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    What Andy said + I recommend making a joint out of 1" and 1 1/4" OD tubing with .035" wall thickness to start. The advantage of using a quarter inch OD difference is that it is easier in the beginning to fillet braze around the "ears" of the miter if they aren't so close in size to the tube it is butted up against. Those diameters and wall thickness are close to what you will be eventually making.


    Don't expect your LWS to have either the materials or knowledge to help you achieve any framebuilding goals. If you buy anything other than C-04 brazing rod made by the Gasflux company with their Type B flux and sold by Henry James Bicycles or rod and flux from Wade Barcosi at Cycle Design, then you are getting off on the wrong foot.


    As someone who has taught framebuilding for years I have pretty strong opinions on how one can best learn. I know what the learning curve is to be able to make a decent frame. Knowing how to teach a skill is different than knowing the skill itself. It actually can be discouraging to just watch a master do a fillet brazed joint. It will look easy and you'll think you can copy the same and then you try it and its all a mess. It begins with the right equipment and materials. During the demonstration there is a lot happening that the mind can't take in all at once or remember everything. How close, how fast, what angle the flame is, how the rod is held, etc, etc, etc. That is why before the demonstration there is a lot of explanation and review of principals. A good teacher knows all the beginner tendencies and how to correct for them before they are made. Let me give you just one example of many. It is a beginner tendency to hold the brazing rod down by one's side (or some distance away) when heating up a joint. When the heat indicators say brass can be added, now it takes them some time to get it in position. In the mean time the flame isn't being paid attention to and bad things happen. It is essential to have the brazing rod be really close to its entry point and be held at a certain angle. Otherwise too much attention is paid to the rod holding hand motion and not enough to the flame motion and things start to go south fast.


    What method one chooses to learn how to braze partly depends on how good one wants to be. If one enjoys messing around for some time on their own with limited resources, then a DIY plan is okay if one doesn't care much about the quality of their first results. If one wants to be really good at it and have a learning curve that doesn't stretch forever, than they need to be taught by an expert that knows both the subject matter and teaching methods for different kind of learners. It really is that simple. I teach some short couple of day classes because I realize some will never have the time or money for a full 3 week class. When I wanted to learn I had to go to live in Europe so I'm probably not overly sympathetic that local training be a requirement.


    Most average students can do a decent fillet brazed joint without much if any pin holes when they follow a training sequence that includes knowing what equipment and materials work best, have both general brazing instruction and are taught specific motions for each type of joint and are given a demonstration that illustrates all of the above.

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    Quote Originally Posted by lostforawhile View Post
    if and when you decide to do this, I can send you some short scrap pieces of 4130, I can probably fill up one of those USPS boxes, the if it fits, it ships deal. We have barrels of the stuff. It would be good to practice on
    Sent you a PM... I'm all over that!
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    Alright gentlemen, I have a quick question. I have still been practicing on scrap tubing from an old 4130 bike that I hacked up. When I finish a fillet, some areas have a really dark(almost black) area around the joint. It is sparse and usually outside of some of the fluxed area. How does one prevent that from happening? Am I not using enough flux? Or, am I not fluxing enough of the tube? I get it to come off, but it's a bear to remove, usually needing a file.

    In other news, this morning I had my "AHH HAA!" moment with my fillets...finally found a nice heat ratio to get more brass in my joints with good penetration =)

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    Quote Originally Posted by lostforawhile View Post
    if and when you decide to do this, I can send you some short scrap pieces of 4130, I can probably fill up one of those USPS boxes, the if it fits, it ships deal. We have barrels of the stuff. It would be good to practice on
    Okay, since I don't have 50 posts, I can't PM... How can I get you a message to arrange this?
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  17. #17
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    Quote Originally Posted by seankanary View Post
    When I finish a fillet, some areas have a really dark(almost black) area around the joint. It is sparse and usually outside of some of the fluxed area. How does one prevent that from happening?
    It's not likely that you can get rid of it. It's carbon precipitation, and if it's outside the fluxed area there is little you can do other than use less heat. It's happening under the flux too, but the flux carries the carbon away from the joint. Gas fluxer seems to help with this, not that it matters.

  18. #18
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    Quote Originally Posted by unterhausen View Post
    It's not likely that you can get rid of it. It's carbon precipitation, and if it's outside the fluxed area there is little you can do other than use less heat. It's happening under the flux too, but the flux carries the carbon away from the joint. Gas fluxer seems to help with this, not that it matters.
    Thanks for the info. I assume this is where the fine tuning of heat and time spent in one area comes into play....... I have been playing around with 1/16 LFB and 3/16 LFB. I had been having problems building a bigger fillet with the 1/16 but much more success with the 3/16 however it needs more heat. Practice practice practice =)

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    Randomhead
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    I'd have to see your results to offer an opinion. here is a bb shell I brazed up with what I consider acceptable carbon precipitation:

    4845108005_f594fa9a5f.jpg

  20. #20
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    ^^that is comparable to the amount I have...except your brazing looks much nicer.

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    Randomhead
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    use more flux if there are cameramen lurking about, that's all I can say Note that there is no visible carbon on the over-fluxed seat tube

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    Will give it a go and report back. I noticed that there is more around the edges of tube, not on a long piece.... like in your picture, the seat tube has none, but the edges around the bb have a little.

  23. #23
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    Quote Originally Posted by David Tollefson View Post
    Sent you a PM... I'm all over that!
    it will probably be next week

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    Quote Originally Posted by unterhausen View Post
    use more flux if there are cameramen lurking about, that's all I can say Note that there is no visible carbon on the over-fluxed seat tube
    Ok...Here are some pics. Be easy on me, still learning.

    photo(5).jpgphoto(6).jpg

    I'm still trying to find a happy place for heat. This morning I tried less heat but noticed more of that carbon precipitation developed because I spent more time trying to heat up the area.. This was not evident on previous tubes when I turned the heat up more. It still cleans up fairly well, I just spend more time with a file.

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    Randomhead
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    the copper means that you cooked the filler. Use less heat. One of the ways to moderate the heat is to move the torch somewhere else. If it really starts getting hot locally, flick the torch away from the frame. If it starts spitting at you/boiling, that's too hot. I would practice with tube sections until you get rid of that. Are you using oxy/acetylene? I wonder if you need a bigger tip on your torch.

    If you find yourself forcing things, then take a few seconds to relax. Point the flame at the ceiling and take a few deep breaths. For whatever reason, most people get frustrated and try to increase the heat. That is exactly the wrong thing to do.

    Don't know what else to say because I barely have any idea of what it is I do while brazing. I shouldn't tell you this, but my goal is to produce a fillet that doesn't need filing. Some days I actually pull that off. I want to get a helmet cam and video myself brazing. I have an extra pair of didymium brazing glasses that I could duct tape to the lens.

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