Advertise on Bikeforums.net



User Tag List

Results 1 to 18 of 18
  1. #1
    Senior Member
    Join Date
    Oct 2004
    Posts
    328
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    brazing canti bosses to rear stays

    I'm looking for advice on how I can add cantilever bosses to the seat stays of a chromoly frame. I've read through

    http://sheldonbrown.com/cantilever-fixture.html

    http://www.cyclingforums.com/archive/index.php/t-42403

    http://koti.mbnet.fi/andhol/15inch.htm

    But may need some advice as to size the bosses for my stays (are they all standard) and perhaps a primer or reference for doing this type of brazing. Also tests for ensuring reliability or valuing worthiness of the braze. The easiest solution would be to pay someone else to do this, but I'm interested in learning how.

    Thanks!

  2. #2
    Senior Member sydney's Avatar
    Join Date
    Jan 2004
    Posts
    9,428
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jasong
    I'm looking for advice on how I can add cantilever bosses to the seat stays of a chromoly frame. I've read through

    http://sheldonbrown.com/cantilever-fixture.html

    http://www.cyclingforums.com/archive/index.php/t-42403

    http://koti.mbnet.fi/andhol/15inch.htm

    But may need some advice as to size the bosses for my stays (are they all standard) and perhaps a primer or reference for doing this type of brazing. Also tests for ensuring reliability or valuing worthiness of the braze. The easiest solution would be to pay someone else to do this, but I'm interested in learning how.

    Thanks!
    UBI has a school.

  3. #3
    lover ....
    Join Date
    May 2004
    Posts
    243
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Make sure you get distance between the bossesc orrect for:L

    1. the width rim you want to run, and
    2. the particular brakes you plan to use (if Shimano - I think their website will have this detail)

    Otherwise you will find brake setup to be a nightmare.
    Riding a bike is not a fashion show

    Super commuter, grease freak, lover ...

  4. #4
    Senior Member
    Join Date
    Oct 2004
    Posts
    328
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    How do mfctrs take this into account, knowing neither of the two?

    Quote Originally Posted by Bike_13
    1. the width rim you want to run, and
    2. the particular brakes you plan to use (if Shimano - I think their website will have this detail)

  5. #5
    You need a new bike supcom's Avatar
    Join Date
    Aug 2002
    Posts
    5,434
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    You will need some way to hold the bosses in the correct place at the correct angle. You will also need a torch to melt the brazing rod. I don't believe a cheap propane torch will do it. You need a welding torch.

    All in all, unless you really want to make a significant investment (or already have the tools) you would be far better looking up a framebuilder.

  6. #6
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    yea, as nice as it is to learn yourself, if something goes wrong your screwed.

  7. #7
    Newbie
    Join Date
    Jan 2005
    Posts
    1
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Use mapp gas with a propane torch set up.
    And instead of brazing, use silver solder. It has a MUCH lower working temp. and is way stronger. They use it to mount tips on lathe tooling.

    Should not be too hard even for your first time.

    Have fun.

  8. #8
    Senior Member mtbikerinpa's Avatar
    Join Date
    Dec 2004
    Location
    PA
    My Bikes
    92 Giant Sedona ATX Custom
    Posts
    1,672
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Probbably the simplest way to make sure you have the spacing is to make a jig that fits tight over a known good frame. Not much, just a bar with tight fitting holes in it. Bolt the bosses onto that and make sure you have the propper radial distance from the axle. Be careful to get the peices up to the propper temperature before applying the solder, but do not take more time than can be helped. Too little heat makes a brittle jointdue to poor penetration of the brazing medium(silver braze is preferable) and too hot will potentially soften the temper of the metal. O would worry more about cold than too much heat.
    A large bead is not neccesary, just a well penetrated complete bead that leaves no gaps or irregularities.
    The parts must be perfectly clean for a good joint. Dirt will impede the process greatly. Apply your flux as per its instructions and heat the joint.
    When cleaned, fluxed, and heated propperly, as with wiring, the joint will wick the braze medium right into the joint. You will know when this happens. Let it cool completely before removing the holding jig.
    Check against your refference again, then mount a brakeset and see if it works propperly. you can figure the rest.
    Speaking as a metal fabricator, It is a basic procedure for me. For most people, I can easily see how it can go south. A lot of steel frames, such as my Sedona have butted tubing, which means the area the brake bosses mount to is tapered to a very thin wall. That saves wieght but it makes the job a little more interesting. For brazing it should not be a problem, but for other modes of weld, it can be a real trick to not melt through.
    As Stated previously, If you have any reservations, find somebody who is familiar with brazing or framework. A person who does brazing or welding for a living could to this operation in a matter of minutes with good quality. More power to ya for trying
    Aviation Mechanic, Bike racer, Fitness Equipment Restorer

    http://pedalmybike.com/userTrackies/myTrackie4758.jpg[/url]

  9. #9
    Senior Member
    Join Date
    Oct 2002
    Location
    Laguna Hills, OC, California
    Posts
    265
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    It is not hard at all to braze-on the bosses. The hardest part is to either buy or make yourself a jig to hold them down and straight while brazing them. On the issue of where to place them, just copy it from another bike or mountain bike. There is a fair amount of adjustability in all the brakes I ever used. The bikes all have different spread of the stays, so there has to be adjustability to fit all the different touring, cross and mountain bikes. Look over a mountain bike and measure the distances off. I do use a cheap MAPP torch ($25) - I built several bikes with it. I never had any structural problems with any of the brazes. BTW, I prefer to use brass on the bosses. Silver is good under lugs, where it flows really nicely under, and with much lower temperature, but it doesn't fill really as good as brass does, and so for this sort of "surface" fill or around dropouts, brass works better. Also, silver is much more easy to overheat and oxydize by someone without much brazing experience, and that can subsequently create dangerously weak joint. The important think is to clean and fit the metal really well first, use generous amount of flux and have a jig that will hold the assembly together and straight. You can buy one, but unless you will do this a lot, I don't think it is cost effective. I built a simple jig from just a drilled strip of steel. It holds the bosses straight, spaced and down with screws and gravity - just hold the bike in a work stand. I've done it on six bikes that I remember so far, and never had any problem, but I am an engineer, not a lawyer, so I will spare you all the disclaimers.

  10. #10
    Senior Member
    Join Date
    Dec 2003
    Location
    Inside the beltway
    Posts
    236
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ComPH
    It is not hard at all to braze-on the bosses. The hardest part is to either buy or make yourself a jig to hold them down and straight while brazing them. On the issue of where to place them, just copy it from another bike or mountain bike. There is a fair amount of adjustability in all the brakes I ever used. The bikes all have different spread of the stays, so there has to be adjustability to fit all the different touring, cross and mountain bikes. Look over a mountain bike and measure the distances off. I do use a cheap MAPP torch ($25) - I built several bikes with it. I never had any structural problems with any of the brazes. BTW, I prefer to use brass on the bosses. Silver is good under lugs, where it flows really nicely under, and with much lower temperature, but it doesn't fill really as good as brass does, and so for this sort of "surface" fill or around dropouts, brass works better. Also, silver is much more easy to overheat and oxydize by someone without much brazing experience, and that can subsequently create dangerously weak joint. The important think is to clean and fit the metal really well first, use generous amount of flux and have a jig that will hold the assembly together and straight. You can buy one, but unless you will do this a lot, I don't think it is cost effective. I built a simple jig from just a drilled strip of steel. It holds the bosses straight, spaced and down with screws and gravity - just hold the bike in a work stand. I've done it on six bikes that I remember so far, and never had any problem, but I am an engineer, not a lawyer, so I will spare you all the disclaimers.

    If you have actually done it, then I'm wrong. But I dont think a MAPP torch gets hot enough for brass brazing. I've used MAPP for silver, no problem. And I've used it to REMOVE braze-ons stuck on with brass, but it doesnt really melt, so that it would flow properly into a joint, like a canti braze-on. It just softens enough so I can pull off the glowing braze-on with pliers. But you're right that brass would probably be preferable because the gap at that kind of joint might be too much for silver. But you really brazed with brass rod using MAPP? It must have been a bugger, and with your whole frame glowing before it flowed-

  11. #11
    Senior Member
    Join Date
    Dec 2003
    Location
    Inside the beltway
    Posts
    236
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jasong
    I'm looking for advice on how I can add cantilever bosses to the seat stays of a chromoly frame. I've read through

    http://sheldonbrown.com/cantilever-fixture.html

    http://www.cyclingforums.com/archive/index.php/t-42403

    http://koti.mbnet.fi/andhol/15inch.htm

    But may need some advice as to size the bosses for my stays (are they all standard) and perhaps a primer or reference for doing this type of brazing. Also tests for ensuring reliability or valuing worthiness of the braze. The easiest solution would be to pay someone else to do this, but I'm interested in learning how.

    Thanks!
    Here's where you get cheap advice- post a question here, and maybe the Man Himself eRichie (Richard Sachs) will join your thread. Careful- it's addictive, pretty soon you'll be searching for a cheap jig- http://frameforum.net/

  12. #12
    Senior Member
    Join Date
    Oct 2002
    Location
    Laguna Hills, OC, California
    Posts
    265
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ZenNMotion
    If you have actually done it, then I'm wrong. But I dont think a MAPP torch gets hot enough for brass brazing. I've used MAPP for silver, no problem. And I've used it to REMOVE braze-ons stuck on with brass, but it doesnt really melt, so that it would flow properly into a joint, like a canti braze-on. It just softens enough so I can pull off the glowing braze-on with pliers. But you're right that brass would probably be preferable because the gap at that kind of joint might be too much for silver. But you really brazed with brass rod using MAPP? It must have been a bugger, and with your whole frame glowing before it flowed-
    Like I said before, I did it, and many times. The whole frame is not glowing, just the area that is being brazed, and I try for it not to glow as much as possible. I don't understand that comment too much, because brazing frames with brass is very common for a very long time - there is nothing unusual about it....

  13. #13
    Senior Member
    Join Date
    Dec 2003
    Location
    Inside the beltway
    Posts
    236
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Of course brass brazing's been around a long time. My comment/question is using MAPP with brass. You said you do it. OK. I just tried it once and couldnt get it hot enough with a basic MAPP (no oxygen tank) torch for the brass to flow, it just got soft without really melting. Maybe I didnt heat it long enough, I chickened out when I was afraid I was cooking my tubes too long. I'd like to try it again if it can be done, because I have a couple of old frames I'd like to modify/repair using brass.

  14. #14
    Senior Member
    Join Date
    Oct 2004
    Posts
    328
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Thanks for the replies, guys. Good starting points.

  15. #15
    dangerous with tools halfbiked's Avatar
    Join Date
    Aug 2004
    Location
    minneapolis
    My Bikes
    fat, long, single & fast
    Posts
    4,502
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by ZenNMotion
    Of course brass brazing's been around a long time. My comment/question is using MAPP with brass. You said you do it. OK. I just tried it once and couldnt get it hot enough with a basic MAPP (no oxygen tank) torch for the brass to flow, it just got soft without really melting. Maybe I didnt heat it long enough, I chickened out when I was afraid I was cooking my tubes too long. I'd like to try it again if it can be done, because I have a couple of old frames I'd like to modify/repair using brass.
    Yes. Great question. I could also justify a MAPP torch for playing around with old crap frames. But I can't really justify a good oxygen rig for hobby use. A definitive statement re: MAPP and brass would be awesome.

  16. #16
    Senior Member
    Join Date
    Dec 2003
    Location
    Inside the beltway
    Posts
    236
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    I posted the question on the framebuilders forum. It seems that MAPP gas will eventually heat a joint up enough for brass brazing. But the steel is tempered because of the long time involved. Thus a weakened joint- definitely not a good idea for canti brake studs. So use silver if you can, or get a real torch, or take your chances, or forget about it.

  17. #17
    Senior Member
    Join Date
    Oct 2002
    Location
    Laguna Hills, OC, California
    Posts
    265
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Well, I guess that if you don't like the answer, keep asking the question so you get the answer you want to hear - someone will agree with you.... As Pokey used to say - there is a lot of applesauce around.

  18. #18
    Senior Member
    Join Date
    Dec 2003
    Location
    Inside the beltway
    Posts
    236
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Sorry, I don't know Pokey- and I'm really not meaning to flame or argue. I just really wanted to know if it could be done safely (brass braze w/MAPP) because I would like to replace some dropouts and braze some canti studs myself, and I don't want to buy an expensive torch just for this. I thought the prevailing wisdom (based on threads on the framebuilding forum- many of those guys do it for a living) was that you can't or shouldn't braze brass with MAPP. Clearly it can be done, as you have done it, though it takes some time (as I have tried, a little). A beginning brazer, such as myself, or the original poster, probably doesnt have the skill to move quickly enough or know how long is too long to expose the joint to a too-cool flame to avoid annealing the steel. My personal choice (though not yours, but that's cool) would be to not attempt it on something like a dropout or a brake attachment point. I kept asking the question because all the information wasn't given in the first place. Anyway, we beat this one to death, huh? Enjoy your home-brews, I'd like to try one myself one day.

Posting Permissions

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