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Discussion Starter #1
having some thoughts on frame building lately, going over methods, probably will use crmo tubing, looks like bronze fillet brazing is the way to go, doesn't overheat the base metal and isn't hard as nuts, this test piece was bent back and forth until it broke, you can tell by the distortion of the tube that the haz wasn't made brittle by the process like tig does

IMG_1490.JPG IMG_1491.JPG
 

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I'm curious as to what you are building?

I've got a couple frames I would like to braze weld and have been getting the most basic info from Eurospares. Any tips, tricks, etc. to give to a new guy? I've torch welded before, but it's been quite some time since I've had practice. Usually just pull out the mig for tabs and brackets, but would rather braze.
 

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When I have done brazed joints on things, it always takes me atleast twice as long because I had precision fit up driven into my head. With MIG and I suppose TIG (I have not done much of that...) you can deal with imperfections in the fitup. Brazing is strongest when its a capillary action between the parts. This goes for bronze brazing as well as plain old tractor supply brazing rods as well as silver soldering bits together. You have demonstrated that bronze brazing, when done properly is way way more than adequate for pretty much any bike frame use. And its pretty :p
 

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Makes perfect sense. Your weld material melts at a far lower temperature then your base material.

& the strength of the weld is dependant on adhesion, instead of melt and penetration.
 

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Discussion Starter #5
I'm curious as to what you are building?

I've got a couple frames I would like to braze weld and have been getting the most basic info from Eurospares. Any tips, tricks, etc. to give to a new guy? I've torch welded before, but it's been quite some time since I've had practice. Usually just pull out the mig for tabs and brackets, but would rather braze.
I'll try to put together a video, I think it comes down to flux application, bronze selection, and heat

and yes, the joints do like to be fit very very well, I coped the tube then came in with a file to get the joint perfect, it's definitely not a production friendly process
 

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Discussion Starter #7
the tube is tacked 4 places, then the braze is just run around the tube, the bronze braze doesn't really pull like a weld does, the temperature only gets to about 16-1700, as opposed to 2500 or more for a weld, so once its tacked, it really doesn't move. really nice feature for frame building as it doesn't add a lot of stresses into a frame built on a jig
 

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Also, why Chromoly? The heat treating sounds like a pain, but it could just be my complete ignorance to the subject. I'm also curious how significant the weight difference would be to mild steel.
 

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Terminology is confusing.

Brazing is what was done for cast lug construction.

What ROC is describing in the UK was referred to as Bronze Welding to differentiate the processes. Filler rods used by Reynolds and RIckman etc were Nickle Bronze IIRC.
 

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Discussion Starter #12
crmo doesn't really need heat treatment if it's not welded, if it is, then you really need to anneal the whole frame, then bring it back to previous condition. crmo isn't stiffer than steel, isn't lighter, but it does have a higher yield strength, which makes it more useful when designing predictably flexible frames, from my research, stiffer frames aren't really better, most modern frames actually have some flex designed in to allow the wheels to twist relative to one another to allow for road following when the bike is leaned way over and the suspension isn't going to function much at all
 

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Just for clarification, that is brazing, and not braze/bronze welding. Am I correct? Capillary action draws into filler rod into the lug. Roc is braze fillet welding.
It's almost akin to soldering, and silver is sometimes used instead of bronze.
The shape and dimension of the lugs can be designed to reduce stress on the tubing, in the area where you have demonstrated a failure is most likely to occur.
 

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Discussion Starter #14
Terminology is confusing.

Brazing is what was done for cast lug construction.

What ROC is describing in the UK was referred to as Bronze Welding to differentiate the processes. Filler rods used by Reynolds and RIckman etc were Nickle Bronze IIRC.
very confusing indeed, the process in the bike world is known as fillet brazing, to differentiate it from brazing or soldering lugs, but not referred to as welding because there's no actual fusion of the base material
 

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I read somewhere that most of the custom frames out of Eur are brazed together for the reason already listed - less heat distortion. From what I understand a brazed weld is as strong as a welded joint. So I am not surprised to see where the test failed on the tube and not in the brazed area.
 

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My understanding is thin wall comoly- needs no post heat treatment if welded correctly And heat treatment is olny needed with the thicker materials. But than again this argument rages on and on web wide. I will believe whats in my books me
 

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Discussion Starter #17
depends on how quickly it cools, if you look at the heat treatment schedules for 4130, bringing it to a high hardness is usually high temperature, then quench, in thin tube, it hits high temperature and then rapidly cools once the weld is done, so in most cases, you wind up with a high hardness and therefore, brittle area near the weld, post weld heat treatment would heat the entire frame, then cool at a set rate to normalize the material and remove hard and brittle areas. i watched some youtube videos on welding chromoly, and every time, the tube snapped cleanly about 1/4" from the weld. that kind of predictability in breaking tells you something... also, I thought it was funny that one of those videos was a famous fabricator, telling everyone "it's not hard welding chromoly!!"
 

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This lincoln Electric page sums up the basice as I have learned previously. They don't mention heat active crayons to guage your pre and post heat if used or needed, You could make or mod a kiln for doing anything the size of a motorcycle the Brazilian shifter-cart racing guys I knew post heated in a kiln on a jig and claimed it took a lot of unwanted spring out of their frames.

TIG Welding Chrome-Moly Tubing
 
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