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  1. #1
    EPP
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    Attaching seat stays to seat lug

    Hi all,

    I'm new to this forum but not completely new to framebuilding. I started the process of building my own frame about 5 years ago, then due to one thing and another the project went off the boil.

    However, I'm now equipped with a shiny new mapp gas torch and have been practising my silver and brass brazing. Which leads me to my question...

    How are seat stays attached to the seat lug without affecting the seat lug filler?

    As far as I know there are three options:
    1. Use brass on the lug and silver for the stays
    2. Use silver on both, brass on both, or silver on the lug and brass for the stays and accept that the lug may be affected temporarily
    3. Shape the lug so that the stays attach directly to the seat tube underneath (though some heat is likely to flow the filler in the adjacent lug?)

    I wasn't able to find any clear info on this forum or the web more widely - any quick hints appreciated!

    Ewan

  2. #2
    Senior Member mudboy's Avatar
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    2.

    However, what I do is use 45% safety-silver for the lug/tube joints, and 56% safety-silver for the stay/tube joints. The 45% has a higher liquid temp so generally will not hit liquid temp when attaching the stays...generally.I think the liquid temp diff is something like 50 degrees C

    I do the same thing with forks, 45% for the steerer/crown, 56% for crown/blades

    Pete
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  3. #3
    Randomhead
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    you have to work very hard to affect the seat lug filler when attaching the seat stays, even if you use brass for the stay attachment and silver for the lug filler. I have seen it happen, but the person who did it was a hack. You can always use Fillet Pro for the stays. I brazed thousands of stays at Trek with silver in the lug and the stays attached with Nickel Silver (think brass, no silver in it).

    If you attach the stays directly to the seat tube, it's gonna break.

    Your mapp torch is going to have a hard time with anything other than silver anyway.

    One more edit. I'm just registering the notion that Pete is doing it backwards. 45 should build a bigger fillet than 56 and thus is more appropriate to put the stays on with. I like to see a nice fillet there.

    I use 56 for both the steerer and the fork legs. Silver remelts at a higher temperature than the original melt. Just try to remove a tube from a lug sometime, you'll see what I mean. The surface tension of the previously solidified brazing material will keep it from moving even if you do get it to a liquid state.
    Last edited by unterhausen; 10-18-10 at 12:23 PM.

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    That was my reaction on the 45 56 stuff also. depending, one could end up with the worst of both worlds, bad penetration with the 45, and small filets with the 56, of course if one knows what one is doing it would be possible either way (i need more help though). I happen to use 45 for everything so I'm not all that fussy, I ended up with 2 pounds of the stuff. With MAPP gas one would have difficulty pulling 45 into lugs anyway.

    It takes a higher temp to loosen the joint than to put it in, so it is rarely a problem.

    There was that method referred to recently where the builder tacked the stays with tig in the jig, then puled the stays and lugs off, and welded them, then did the silver after the welding. Not appicable here though.

  5. #5
    EPP
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    Cheers guys, very helpful.

    I see what Pete is getting at - use a filler with a lower liquid temperature for the stays to reduce the chance of melting the lug filler. Experience seems to show it's not really an issue though, so I may go with 56 silver for the lug and stays.

    There's a well known builder near where I work, and I popped in today to ask if he had any bits of old seat/chainstay lying around that I could have for practice (quick to miter so i can spend more time brazing them to an old frame tube). I asked him the same question posted here and he suggested brass for the lug and silver for the stays, but then showed me a bare 953 frame done, as required, fully with silver. Looked great, and his particular signature method of mitering stays to the sides of the lug doesn't require a fillet at all. Minimal filler in the joint, and he's been doing it that way forever.

    I thought I was going to be limited to silver with the mapp torch too. But I've been surprised at how much heat mine produces (a Turbotorch with hose), which has been ample to create small brass fillets. Haven't tried flowing brass around a lug, but I reckon it would work fine. I think it's map pro gas, which I understand might burn hotter than standard mapp.

    Cheers,

    Ewan

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    (New guy here...first post...greetings...)

    I've been practicing my brazing using sections of 1.125" tubing over 1" tube (pretend lugs). I'm using Safety-Silv 56 and Harris Black flux.

    I bought one of the Bernzomatic MAPP/air torches because I can't justify an O/A setup yet (in the face of preschool tuition, health insurance, car/house repairs, etc.). I went with the Bernzomatic BZ8250HT, which includes a 5' hose. It supposedly has a "swirl burner", which sounds fancy.

    My limited experience is that this MAPP torch produces a good deal of heat. Granted, I'm not doing anything massive like a fork crown, but I can easily get the tubing cherry red. In fact, I'm working on practicing trying to put less heat in the joint. I've been trying to "pull the silver" like Paterek demos in his video, but I seem to get the joint too hot. So far, I'm getting what seem to be pretty good brazed joints. I've even ground several of them open to confirm that I'm fully filling the joint.

    I know Mapp/air burns (theoretically) at several hundred degrees less that O/A. Maybe these new torches are more efficient than the old ones?

    One disadvantage I see (compared to Paterek's video) is that his flame is smaller/more focused than mine.

  7. #7
    Randomhead
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    the real issue is how quickly you can get the area up to temperature. If it requires that a large area be heated, you don't have any control over where the filler is going to go. Additionally, I'm curious about the statement that you are getting the joint too hot when you "pull the silver." MAPP users have reported that they have a lot of problems with overheating. This is due to how long it takes to get up to temperature. I'm tempted to try my mapp torch so I can talk more intelligently about this, but I don't think I need the headache

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    "One disadvantage I see (compared to Paterek's video) is that his flame is smaller/more focused than mine."

    To a certain extent the AO is too hot,and the aspirated torches are too cold. Paternek uses a flame not too far from a welding flame, and as a result he spends a lot of time heating air. There is a view that you can only braze properly if you work the silver around with a small flame, but from what I can gather there are other options, such as a gas hearth, gas multi head flames, rosebud heads, or OA torches run hard. I think it could be argued that when using aspirated torches one should retain as much heat as possible (hearth), or use multi or larger heads. There are propane heads you can melt a frame down with. I have experimented with some of this stuff, but it is hard to get decent results when one is feeling one's way at every step.

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    Randomhead
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    hearth brazing is pretty interesting. They often used internal charges of material. But you have no control if you stab the wrong part of the bike with the filler. I'm guessing that's why there are often lumps of filler everywhere on some of the European bikes from the '70s bike boom. I always liked using a lot of heat for brazing lugs, and flick the flame away from the lug when it hits the right temperature. One thing is for sure, I hate waiting once the flux has gone glassy.

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    Cool.

    I always try to site this video at least once a week. Around 2:30 they start to pour on the flame with a noisy big torch, compared to Paternek, and not a lot of flicking. I'm not making a point here, I just like seeing how different people do it.

    http://www.youtube.com/watch?v=TMA8X5pk2kI

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    Randomhead
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    I thought everyone in that clip with a hand torch moves the torch at least as much as I do. There is a very short clip of Raleigh hearth brazing -- frustrating that they didn't show the whole process

  12. #12
    EPP
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    I did a quick experiment with my mapp torch to determine what was the cause of my scorched flux. First, I brushed a bit of flux on a bare tube and slowly brought it up to temperature and checked by flowing a small bit of silver on the surface of the tube. Then I held the area at that temperature for a couple of minutes or more, being careful not to bring any of the tubing past a dull cherry red by flicking the torch away. I deliberately scorched a small area just out of interest, then turned the torch off. Compared to the scorched area, the rest of the flux retained a glassy look despite being held at temperature for a long time.

    Just now, I took a practice lug I had brazed to the end of a tube, gave it a quick clean, fluxed it and got the torch on it. Within 20-25 seconds the tube just beyond the lug was cherry red (heating too quickly relative to the lug itself due to my poor torch technique!) and by 30 seconds I was flowing the silver in the joint. Maybe not the most representative test as I was just re-melting pre-existing filler, but that seems to be pretty quick to me. I really do have to be careful with not locally overheating the flux (which I even did on this very brief test).

    Loved the youtube clip! My mapp torch has a smaller flame than the one they use...

    I'm not trying to say everything people say about mapp is wrong, just curious to understand what the differences really are. I had one brief experience with oxy acetylene many years ago and remember it putting out much more heat! I just don't have enough experience to make a meaningful comparison.

    When I get some more practice lugs I'm gonna film my brazing attempt and post it for interest.

  13. #13
    Senior Member mudboy's Avatar
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    Quote Originally Posted by Peterpan1 View Post
    Cool.

    I always try to site this video at least once a week. Around 2:30 they start to pour on the flame with a noisy big torch, compared to Paternek, and not a lot of flicking. I'm not making a point here, I just like seeing how different people do it.

    http://www.youtube.com/watch?v=TMA8X5pk2kI
    I'd assume the Taylors were using brass? I think Paterek was more a proponent of silver.
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  14. #14
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Peterpan1 View Post
    Cool.

    I always try to site this video at least once a week. Around 2:30 they start to pour on the flame with a noisy big torch, compared to Paternek, and not a lot of flicking. I'm not making a point here, I just like seeing how different people do it.

    http://www.youtube.com/watch?v=TMA8X5pk2kI
    At Trek I used a big ol' rosebud tip with oxy-propane and Gasflux. It heated up right quick; I'd pour in the brass under the stays and be out of there before the joint knew what had happened. No charring, no clean-up.

  15. #15
    Senior Member mudboy's Avatar
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    John, how does Gasflux work? Does it completely do away with the need for paste flux application before applying flame?

    Followup (and I don't mean for this to be a thread derail), do you still use Oxy-Propane, and if so, could you give details of your setup? I want to buy my first torch after the new year and I'd prefer not to use Acetylene because it's so sooty.

    Thanks,

    Pete
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  16. #16
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by mudboy View Post
    John, how does Gasflux work? Does it completely do away with the need for paste flux application before applying flame?
    At Trek we used paste flux in addition to the gasflux, but some people find just plain Gasflux works well, especially for fillet brazing. Here's a diagram of the set up:


    It works best with brass. With silver, I found the bright green flame made it difficult to judge when the work was hot enough to melt the rod.

    Followup (and I don't mean for this to be a thread derail), do you still use Oxy-Propane, and if so, could you give details of your setup? I want to buy my first torch after the new year and I'd prefer not to use Acetylene because it's so sooty.
    No, I use oxy-acetylene now, without Gasflux (I do use Gasflux *paste* flux, though -- IMO the best flux on the market). Acetylene is only sooty until you get the oxygen properly adjusted. After that it's clean.

  17. #17
    Senior Member bleedingapple's Avatar
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    but would oxy-propane be suitable until an oxy-acetylene setup can be put together? can you do lugs and fillet with oxy-propane?

    side question? do you put paste flux on the tube before you put it in the lug?
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  18. #18
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by bleedingapple View Post
    but would oxy-propane be suitable until an oxy-acetylene setup can be put together? can you do lugs and fillet with oxy-propane?
    Yes, and yes. Oxy-propane is entirely suitable for brazing; there's no need to think of it as inferior to oxy-acetylene for that purpose.

    side question? do you put paste flux on the tube before you put it in the lug?
    Yes, inside and out. And reapply after assembling the joint for brazing.

  19. #19
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    One thing Freddy Parr was saying is that for those who want Gasflux in-line because it keeps the flux blanket in a wider area and needs less clean-up, that it contaminates the other flux you may use, and could be disastrous, or sub-optimal. I gather the idea is that if you use stuff like fillet pro, etc... that have specialized flux, and you contaminate that with inline Gasflux, then you have a problem. That does sound obvious, but it comes up as more builders may be migrating to one brand or other of super braze/flux. Then Mr ATMO will jump into these threads and say in-line flux use is not as craftsman-like as might be. All of which only serves to relieve me of feeling I need a gas-fluxer. Though I wish I could easily get their paste flux locally.

  20. #20
    Randomhead
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    Fred just said not to mix his flux with something else. I think mixing most fluxes with each other is not dangerous because they aren't using anything different from each other.

  21. #21
    Old fart JohnDThompson's Avatar
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    Quote Originally Posted by Peterpan1 View Post
    One thing Freddy Parr was saying is that for those who want Gasflux in-line because it keeps the flux blanket in a wider area and needs less clean-up, that it contaminates the other flux you may use, and could be disastrous, or sub-optimal.
    That may be true. At Trek, we used Gasflux in-line along with Gasflux-brand "Type B" paste flux. They seemed to be compatible, and even without in-line Gasflux, I consider their Type B paste flux to be the best brass flux I have used.

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