Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 01-20-05, 12:09 PM   #1
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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!
jasong is offline   Reply With Quote
Old 01-20-05, 12:12 PM   #2
sydney
Senior Member
 
sydney's Avatar
 
Join Date: Jan 2004
Bikes:
Posts: 9,428
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
sydney is offline   Reply With Quote
Old 01-20-05, 06:10 PM   #3
Bike_13
lover ....
 
Join Date: May 2004
Bikes:
Posts: 243
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
Bike_13 is offline   Reply With Quote
Old 01-22-05, 04:39 PM   #4
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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)
jasong is offline   Reply With Quote
Old 01-22-05, 04:50 PM   #5
supcom
You need a new bike
 
supcom's Avatar
 
Join Date: Aug 2002
Bikes:
Posts: 5,433
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
supcom is offline   Reply With Quote
Old 01-22-05, 05:43 PM   #6
phantomcow2
la vache fantôme
 
phantomcow2's Avatar
 
Join Date: Aug 2004
Location: NH
Bikes:
Posts: 6,266
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
yea, as nice as it is to learn yourself, if something goes wrong your screwed.
phantomcow2 is offline   Reply With Quote
Old 01-23-05, 12:46 PM   #7
rockmup
Newbie
 
Join Date: Jan 2005
Bikes:
Posts: 1
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
rockmup is offline   Reply With Quote
Old 01-23-05, 01:49 PM   #8
mtbikerinpa
Senior Member
 
mtbikerinpa's Avatar
 
Join Date: Dec 2004
Location: PA
Bikes: 92 Giant Sedona ATX Custom
Posts: 1,713
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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
mtbikerinpa is offline   Reply With Quote
Old 01-24-05, 05:19 PM   #9
ComPH
Senior Member
 
Join Date: Oct 2002
Location: Laguna Hills, OC, California
Bikes:
Posts: 265
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
ComPH is offline   Reply With Quote
Old 01-26-05, 07:20 PM   #10
ZenNMotion
Senior Member
 
Join Date: Dec 2003
Location: Inside the beltway
Bikes:
Posts: 236
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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-
ZenNMotion is offline   Reply With Quote
Old 01-26-05, 07:27 PM   #11
ZenNMotion
Senior Member
 
Join Date: Dec 2003
Location: Inside the beltway
Bikes:
Posts: 236
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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/
ZenNMotion is offline   Reply With Quote
Old 01-28-05, 11:07 AM   #12
ComPH
Senior Member
 
Join Date: Oct 2002
Location: Laguna Hills, OC, California
Bikes:
Posts: 265
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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....
ComPH is offline   Reply With Quote
Old 01-28-05, 01:16 PM   #13
ZenNMotion
Senior Member
 
Join Date: Dec 2003
Location: Inside the beltway
Bikes:
Posts: 236
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
ZenNMotion is offline   Reply With Quote
Old 01-28-05, 03:09 PM   #14
jasong
Senior Member
Thread Starter
 
Join Date: Oct 2004
Bikes:
Posts: 328
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Thanks for the replies, guys. Good starting points.
jasong is offline   Reply With Quote
Old 01-28-05, 03:48 PM   #15
halfbiked
dangerous with tools
 
halfbiked's Avatar
 
Join Date: Aug 2004
Location: minneapolis
Bikes: fat, long, single & fast
Posts: 4,502
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
halfbiked is offline   Reply With Quote
Old 01-31-05, 02:45 PM   #16
ZenNMotion
Senior Member
 
Join Date: Dec 2003
Location: Inside the beltway
Bikes:
Posts: 236
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
ZenNMotion is offline   Reply With Quote
Old 01-31-05, 03:35 PM   #17
ComPH
Senior Member
 
Join Date: Oct 2002
Location: Laguna Hills, OC, California
Bikes:
Posts: 265
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
ComPH is offline   Reply With Quote
Old 02-01-05, 03:39 PM   #18
ZenNMotion
Senior Member
 
Join Date: Dec 2003
Location: Inside the beltway
Bikes:
Posts: 236
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(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.
ZenNMotion is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:18 AM.