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Framebuilders Thinking about a custom frame? Lugged vs Fillet Brazed. Different Frame materials? Newvex or Pacenti Lugs? why get a custom Road, Mountain, or Track Frame? Got a question about framebuilding? Lets discuss framebuilding at it's finest.

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Old 03-08-06, 05:03 PM   #1
seeker333
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I have a dedacciai steel mtb frame that i use on road / bikepaths only, no rough stuff.

The frame developed a ~7 mm long hairline crack shortly after i built it up, at the interface of the right chainstay to dropout, on the bottom side, extending ~1/3 across width of joint. The dropout is breezer brand with single eyelet, and is brass brazed to the stays. China built bianchi branded frame.

It has been this way for months and i have continued to ride it ~4,000 miles. I put a mark on it to mark end of crack - it has not changed since i first discovered it.

So i've been thinking of getting a cheap benzomatic mapp rig, the special one with the hoses and small tip. And some brass rod.

I've soldered many things and can do this fine, so i expect i can make a simple bicycle frame repair.

Here's my question: How do i fix this joint? I'm guessing i need to file/cut down directly thru the cracked joint to some depth, say ~2 mm, clean, then fill her in with brass, cool then file sand and paint. I recall theres some flux or equivalent required also.

Am i close? Thanks for any advice.

PS - What kind of brass alloy should i be looking for at the local welding supply shop? The folks that work there don't seem to be familiar with the phrase "brazing", or the general concept of using brass rod to join steel.

Last edited by seeker333; 03-11-06 at 10:36 PM.
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Old 03-11-06, 10:38 PM   #2
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gee, no one knows how to fillet braze here on the framebuilders forum?
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Old 03-12-06, 12:00 AM   #3
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It's hard to visualize how you go about doing this repair. Perhaps you could post a picture? Call up Bringheli or Henry James if you still need supplies.

In any case, I'm surprised that you want try to repair this rear dropout junction using a little MAPP gas rig and brass rods. Not sure if you can generate enough heat with the MAPP rig to melt and flow the brass ok. Anybody have an idea to help this guy out?
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Old 03-12-06, 12:41 AM   #4
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You should have no problem flowing brass with a MAPP rig, I agree with bell on needing a photo if possible to give you a better idea of how to proceed. If you are going to use mapp, depending on the size of the dropout and chainstay you may have to use a heat reflector. I think it should be an easy fix only shame will be the paint.
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Old 03-12-06, 03:41 PM   #5
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Quote:
Originally Posted by bellweatherman
It's hard to visualize how you go about doing this repair. Perhaps you could post a picture? Call up Bringheli or Henry James if you still need supplies.

In any case, I'm surprised that you want try to repair this rear dropout junction using a little MAPP gas rig and brass rods. Not sure if you can generate enough heat with the MAPP rig to melt and flow the brass ok. Anybody have an idea to help this guy out?
Well, i have read of and seen pics of entire frames built with these mapp rigs. Some right here on these forum.

You can determine brass melting point, and temperaure range of mapp flame, and...
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Old 03-12-06, 03:42 PM   #6
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Quote:
Originally Posted by Andreasaway
You should have no problem flowing brass with a MAPP rig, I agree with bell on needing a photo if possible to give you a better idea of how to proceed. If you are going to use mapp, depending on the size of the dropout and chainstay you may have to use a heat reflector. I think it should be an easy fix only shame will be the paint.
Not worried about the paint.
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Old 03-13-06, 10:53 AM   #7
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I would suggest you buy the torch, don't get the Oxy-Mapp get the single fuel torch, and practice on some scrap steel and then have at it. It sounds as though it was just an issue of lack of filler. Photo's Please
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Old 03-13-06, 01:44 PM   #8
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What is cracked?

- the paint
-the stay
- the drop
-the drop is pulling out from the stay
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Old 03-14-06, 12:23 AM   #9
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I would suggest you buy the torch, don't get the Oxy-Mapp get the single fuel torch, and practice on some scrap steel and then have at it. It sounds as though it was just an issue of lack of filler. Photo's Please
It may very well be inadequate filler. Actually its just overall poor worksmanship.

The robot tig welds at the head tube are perfect. BB welds pretty neat looking too but i think they're human made.

Looks like a different dude came on at shift change to do the dropouts, theyre kinda sorry looking. Since the frame has a disc brake mount (not the fancy dropout integrated type), the single eyelet sorta was too close for his liking, so the left dropout was rotated ~20 degrees, then attached. When you look from side, one eyelet at 12:00, one at 10:00.

I had a minor mental breakdown trying to figure out why i couldnt mount a perfectly good proven blackburn rack on the frame when i first got it.
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