Results 1 to 25 of 25
  1. #1
    mtbr member
    Reputation:
    Join Date
    Oct 2008
    Posts
    12

    Need help brazing dropouts

    Hello all. I have been working my way through my first build (steel lugged road bike) and I have run into a problem that I need some help with.

    I am struggling with brazing my dropouts into my chain stays. I am using a O/A torch with gasflux C-04 brass rods and "type B" flux (reco from Henry James). The ends of my stays are plain sawn and I want to tab and slot them and fill with brass. My problem is that I can't get the brass to penetrate down into the stay to fully wet out the tab I have cut. My brass just seems to build up at the opening without flowing down into the stay. I think I have one of two problems - either I am not using enough heat, or I am using the wrong rod.

    Anyone have any advice? What braze material are others using in this configuration? Am I expecting too much penetration? I really want to stay with the plan I have now, but at this rate I feel like I am going to need to dome the tubes and use silver.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Apr 2012
    Posts
    193
    Can you post a pic?
    I'm guessing not enough heat, but wait for more experienced answers.
    Were the stays just getting cherry red?
    http://www.tempil.com/wp-content/plu...rrous_2010.pdf
    The flux turned into liquid with no bubbles?
    cheers
    andy walker

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jan 2008
    Posts
    102
    Are the dropouts stainless perhaps?

  4. #4
    mtbr member
    Reputation: toby_g's Avatar
    Join Date
    Jul 2008
    Posts
    30
    Without pictures it is hard to say, but assuming it isn't stainless I would guess heat is the issue. If the dropout isn't hot enough, the molten brass will sink its heat into the cooler dropout and solidify.
    It is easy to heat the thin walls of the stays long before the dropout is at the correct temperature (it is ~5mm thick, compared to the 0.8mm of the stay). Initially focus the heat onto the dropout, keep the flame directed away from the stays. Only once the colour of the dropout changes to a dull red should you move the torch towards the stays; they will heat quickly. Now is the time to introduce the brass rod.

    I hope this helps, good luck
    Last edited by toby_g; 10-08-2013 at 06:30 AM. Reason: Spelling, clarification

  5. #5
    650b me
    Reputation: golden boy's Avatar
    Join Date
    Oct 2008
    Posts
    1,030
    All I can do is agree with Toby_G. I found brazing in the dropouts the most difficult part. It's such a touchy-feely thing. I think heat control is the key. Gotta heat up the dropout first before focusing on the ends of the stay. Direct the flame on the dropout down inside the stay as far as possible. Also the sides of the dropout where the stay is slotted.

    Good luck! Maybe Garro will weigh in.

  6. #6
    mtbr member
    Reputation:
    Join Date
    Oct 2008
    Posts
    12
    Forgot to mention that my dropouts are mild steel. Also wanted to clarify that I am still practicing on plain tube and steel plate - no chainstays were harmed generating this question (yet). I will try to shoot some pictures tonight.

    I am definately heating up the dropout first and moving to the tube, but I cant seem to get the tabbed portion of the dropout that is burried in the tube hot enough. It may be more accurate to say I cant get all of the pieces hot enough at the same time. Perhaps I just need to get way more agressive with the heat - I may try that tonight to gain some understanding of the breakboints.

    Is this brass alloy (gasflux C-04) a common one for this application? I assume it is, but I have limited knowledge of what others are using. I am wondering if I would be better off with a low % silver that might wick better. The brass seems to want to build up right away and not flow.

  7. #7
    Moderator Moderator
    Reputation:
    Join Date
    Jan 2004
    Posts
    3,924
    More heat. If you are using practice scrap, forget the brass for a moment and just heat things up until you melt the steel, just to watch the color transitions and practice waving the torch around to get things evenly hot. Heck, gas weld some stuff together while you're at it, it's fun.

    Also remember that the metal will conduct the heat, so when you're trying to get the dropout hot, you don't have to have the flame on the chainstay/slot portion the whole time. Put plenty of heat into the dropout until it's starting to change color a little, then move to the actual joint area.

    If your filler is still balling up when the whole joint is a dull red, you are using the wrong flux or rod or something is stainless. Otherwise, more heat.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  8. #8
    Framebuilder
    Reputation: Live Wire's Avatar
    Join Date
    Aug 2007
    Posts
    419
    Quote Originally Posted by boyd2 View Post

    Is this brass alloy (gasflux C-04) a common one for this application? I assume it is, but I have limited knowledge of what others are using. I am wondering if I would be better off with a low % silver that might wick better. The brass seems to want to build up right away and not flow.
    The only way that will happen is if you don't have enough heat and/or (to a lesser extent) flux.
    With plenty of flux, put all of your heat into the plate at first. Alternate side to side to keep it even. When the plate is at temp, then bring the heat down to the tube and pull in the brass.
    Easy to do...kinda hard to explain!

  9. #9
    Randomhead
    Reputation:
    Join Date
    Sep 2008
    Posts
    1,036
    if you try to use silver, it will just be all over the outside because you need better heat control for silver. You have to get the heat under control. You have to dump heat into the dropout more than you think. Heating up the tabs will help a little, but it's the main body of the dropout that you need to put heat into. The brass will help with heat conduction once you get the plate to temp. Once you get the heat right, you will be able to keep feeding brass in until you get sick of it.

    The other thing I always keep in mind is patience. It's not going to work better if you try to rush it.

    I almost wonder if it wouldn't help to just flow brass around on a practice piece of plate

  10. #10
    mtbr member
    Reputation: bobbotron's Avatar
    Join Date
    Nov 2007
    Posts
    1,297
    Quote Originally Posted by Walt View Post
    Heck, gas weld some stuff together while you're at it, it's fun.
    Second the gas welding suggestion, it's so much fun!

    This was my least favourite joint to braze, the stays are so thin, and the dropouts so thick, I was quite worried about cooking the stays the whole time.

  11. #11
    Randomhead
    Reputation:
    Join Date
    Sep 2008
    Posts
    1,036
    I find gas welding a little frustrating, but then again, I usually try to gas weld things that are too thick for my torch.

    I think drops may be one of the easier joints once the clue-bird lands. Not to diminish how hard it is for a beginner. Hardest part for me is marking out the slots

  12. #12
    mtbr member
    Reputation:
    Join Date
    Jul 2007
    Posts
    113
    If using a chunky dropout, I sometimes drill a hole in the bit of tab buried in the stay just to lose a bit of mass. If you are struggling to get the heat down there, then silver won't help as it just runs towards the hottest bit (as does brass but maybe not with such fluidity).

  13. #13
    650b me
    Reputation: golden boy's Avatar
    Join Date
    Oct 2008
    Posts
    1,030
    Quote Originally Posted by mickuk View Post
    If using a chunky dropout, I sometimes drill a hole in the bit of tab buried in the stay just to lose a bit of mass.
    Interesting idea. Seems like this could strengthen the joint if the braze fills the hole.

  14. #14
    mtbr member
    Reputation:
    Join Date
    Feb 2013
    Posts
    40
    Lots of flux, heat the dropout not the tube - when the dropout is turning red, apply brass to the dropout first and let it wet out, then add more brass to fill in. Then heat all over and the brass will suck down in happily.

    Once you get the hang of it, dropouts are quick and easy to do. You just need to learn how to control temperature when you've got thick and thin parts.

  15. #15
    mtbr member
    Reputation: coconinocycles's Avatar
    Join Date
    Sep 2006
    Posts
    993
    All parts must be the same temp.
    - Steve Garro, Coconino Cycles.
    steve garro el jefe/el solo. coconino cycles www.coconinocycles.com www.coconinocycles.blogspot.com

  16. #16
    mtbr member
    Reputation:
    Join Date
    Oct 2008
    Posts
    12
    Thanks all for the advice. It really helped. I was finaly able to get back out to the barn and do some bike work this afternoon. I found I was definately brazing at too low a temperature. I ramped the temp way up and got the results I was looking for. I think I was too used to using 56% silver on thinner material (lugs) and so much heat just felt wrong. I was able to balance the heat between the thick DO and the tube fairly well, but I definately overheated the very tip of the tube trying to get heat down inside. A few more practice sessions and I should be ready for the real thing.

    Obviousy I err on the side of not enough heat, but how does one know if you are overheating a tube. Is is color only?

  17. #17
    Randomhead
    Reputation:
    Join Date
    Sep 2008
    Posts
    1,036
    bronze will spit at you if you are overheating it. If you see copper when you are done that means it was overheated

  18. #18
    Harrumph
    Reputation: G-reg's Avatar
    Join Date
    Jan 2004
    Posts
    1,561
    The thick stuff takes more energy to get up to temp, but it also retains that heat for longer. So focus on heating just the drop out material, and if the relatively thin slotted stay starts getting too hot take the torch away. The thinner metal will cool off quickly, and the thick dropout will retain heat. So a little cool off period for the stay will not cool the dropout much....relatively. Do this off an on and you can get everything up to the same temp without torching the ends of your stays. Hopefully that makes sense, and more importantly it applies to every other joint on a frame. It's something that is instinctual to an experienced brazer. I've personally a long way to go, but wrapping my head around managing energy in this manner has made a huge difference in my brazing.
    Slowly slipping to retrogrouchyness

  19. #19
    builder of frames
    Reputation:
    Join Date
    Mar 2010
    Posts
    67
    Others have described how to braze stamped or forged dropouts to chainstays well. I'll just add a few things and say it a bit differently. The complication is not just that the dropouts are thicker and the chainstays thinner but that air between the tab of the dropout and the inside the stay keeps it insulated from the heat of your flame that can't reach it directly. This is why it is difficult to get the tab up to brazing temperature. The solution requires a two stage process. First heat the dropout near the chainstays with horizontal strokes to get it up to brazing temperature. The tip of the flame should be almost but not quite touching the dropout. When it gets red (indicating the temperature brass will now melt and stick to it) you start adding brass right at the left or right side (depending on if you are right or left handed) where the two pieces touch. This connects the 2 pieces together so the heat from one can transfer to the other. This connection keeps the thinner chainstay from overheating when the flame is pointing toward it and now allows heat to reach the dropout tab.

    Your flame motion now changes from horizontal to downward strokes (only as far down as you want the brass to go) and pull it back a bit (because you stop bringing the metal up to temperature and start keeping it within brass melting temperature window). This change from heating up to keeping it at brazing temperature necessitates a change in motion and is the beginning of the 2nd stage. It takes a different approach and finer control. Now add brass until the chainstay opening is full. This may require flicking the flame off and on the junction to keep it within brass's (really it is bronze) brazing temperature window. Now you are ready to go to stage 3 which how you do it depends on how you want the chainstay/dropout junction to look.

    One change that I encourage beginning builders to do that is different from standard practice is not to slot the chainstays. Because it is likely they won't have as strict heat control, brass will just bleed out all over the stay creating a mess they just needs to be filed off. Instead the dropout tab can be extended to fit further into the chainstay by filing off some of the top and bottom edge. in other words the dropout tab is filed so it fits inside the chain stay hole.

  20. #20
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Posts
    445
    Doug

    By filing the tab and fitting inside the chainstay hole, would this not make it more difficult to get heat down further into tab? I'm guessing the tab would be 15-20mm long by this method and you could only concentrate heat to the accessible part of the dropout, where as with a slot, you can encourage heat along the tab to slots end.

    Eric
    If I don't make an attempt, how will I know if it will work?

  21. #21
    Harrumph
    Reputation: G-reg's Avatar
    Join Date
    Jan 2004
    Posts
    1,561
    I feel the need every once and a while to point out how mind blowing it is that folks like Walt/Doug/Steve drop down to the internet enabled newbie level, and give honest non condescending advise. Michael Jordan just gave you tips on a lay up, soak it in.
    Slowly slipping to retrogrouchyness

  22. #22
    builder of frames
    Reputation:
    Join Date
    Mar 2010
    Posts
    67
    The best way to learn how to braze a particular joint is to watch an expert. Written or verbal descriptions have to be translated into motion that often isn't perfectly understood. The difference between brazing success and a mess is small subtle torch movements. Some students catch on right away while others struggle. Some never get it. Brazing a dropout with an extended tab entirely within the chainstay hole is not difficult once it has been explained and demonstrated by someone who can break down the process down into small definable steps. It helps knowing common rookie mistakes and how to avoid them. Just for context, I've taught framebuilding classes continuously since 1976. In that time I've been able to refine methods and explanations that fit the abilities of a beginner. The majority of students get the basics of brazing pretty quickly when they read how to do it, then have it is verbally explained, actually demonstrated with commentary and finally are watched over while they do it themselves. The problem for them in brazing up a flat dropout to a chainstay is that they usually take a bit long to analyze what they are doing while brazing. There is a lag time between recognition and action. This most likely leads to melted brass leaking out the slots because they haven't yet learned instant on off torch control. Just filling up a hole is easier. The thing that is the most challenging with my suggested method is the transition from just heating up the dropout to brazing temperature and then pointing the flame at just the right place to start adding brass. Actually doing a dropout/chainstay is a great place to start learning brass brazing because their thickness can absorb some rookie mistakes. Adding brass above the chainstay opening can get one used to adding and removing heat to control where it will go.

  23. #23
    mtbr member
    Reputation:
    Join Date
    Oct 2008
    Posts
    12
    I absolutely agree that the quality of advice I have gotten on this thread is fantastic. Thanks all for the input. I think that I will be ready to try the real thing after a few more practice pieces. I am treating this first frame as a learning experience, so in any case the risk is not too high.

  24. #24
    650b me
    Reputation: golden boy's Avatar
    Join Date
    Oct 2008
    Posts
    1,030
    Quote Originally Posted by G-reg View Post
    I feel the need every once and a while to point out how mind blowing it is that folks like Walt/Doug/Steve drop down to the internet enabled newbie level, and give honest non condescending advise. Michael Jordan just gave you tips on a lay up, soak it in.
    Agreed. I will be printing out Doug's posts for reference. Thanks Doug!

  25. #25
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Posts
    445
    Thanks Doug. I very much enjoy your explainations, very simple and clear. This is a good thread indeed.

    Some history from my perspective. When I started frame building I was self taught, I am finding that threads such as this one crystalizes what I learned and put into practice over my 2 year journey in the early 1980's. Back then, I began with Reynolds 531 tubing and Campagnolo forged horizontal dropouts. The chainstays that I was supplied with came bullnosed and already slotted ex factory, so it was natural to assemble them that way. The dropouts were I believe about 4mm thick at the tab and the slot was a snug fit. The Reynolds stays at that time were very small in diameter but thick walled. Probably why I did not find this task to difficult. Later, I used Columbus SL, which also came pre-slotted, but cut square at the dropout end. These were of a larger diameter, but much thinner walled and are a fore-runner to the present day with the exception that todays D/Outs are up to and over 5mm, so I can see how a newb will struggle. I used to fit a shaped plug up each side of the opening and it would even out the temp variations. But that was my solution, right or wrong.....

    Anyway, thanks guys for the discussion.

    Eric
    Last edited by Eric Malcolm; 10-14-2013 at 07:57 PM. Reason: spelling
    If I don't make an attempt, how will I know if it will work?

Similar Threads

  1. brazing dropouts
    By s4gobabygo in forum Frame Building
    Replies: 21
    Last Post: 12-06-2012, 02:21 PM
  2. Another Brazing Question
    By CurbDestroyer in forum Frame Building
    Replies: 15
    Last Post: 10-31-2011, 10:55 AM
  3. Stainless brazing
    By Levi Strauss in forum Frame Building
    Replies: 8
    Last Post: 05-27-2011, 04:08 PM
  4. Brazing, what do you use
    By jfdupuis in forum Frame Building
    Replies: 7
    Last Post: 05-07-2011, 01:45 PM
  5. Brazing with propane
    By TimT in forum Frame Building
    Replies: 6
    Last Post: 05-03-2011, 05:43 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •