brazing a frame

skyrush2 said:

o my god dude ,,freakin listen..

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Really dude, me thinking Darwin Award candidate!

Beercan

monkey wrench said:

...i understand that if done properly they ...

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That is exactly the problem, it is real easy for most people
to make a poor join by Brazing, and it will probably look fine,
until it is too late.

I've seen many English Formula car chassis,that were completely Brazed; no problem.They stand up fine, even in a crash. They are assembled by professionals.

I've also seen a home built Formula car that was Brazed,
and came apart in a crash. The car passed tech, and raced
for a couple years at least. Luckily, the driver lived to tell about it.

First choice is welding: MIG, TIG, OA, Arc. Your choice.

My distant second choice would be Brazing, with Bronze rods,
but only if done by a very experienced OA welder.

If you like the look of Bronze, you can always braze over
a proper steel weld. Some bike guys do this to get nice fillets.

Unkl Ian said:

If you like the look of Bronze, you can always braze over
a proper steel weld. Some bike guys do this to get nice fillets.

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Finally a great idea. That was worth going through all this mess to hear.

thanks. i'll drop it.

monkey wrench said:

i respect your opinions and i will concider tig as an option. but i believe you are underestimating the stregnth of brazed joints. i understand that if done properly they are stronger then mild steel, 50,000+ psi. in my destruction tests the joint does not fail, its the steel that stretches and the joint holds. additionaly the lower heat used and the fact that the parent material (steel) does not melt you have a lower occurance oxidation and impurities entering the weld and causing future cracks. which is the reason many folks purge with argon.

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I can sympahise with your logic. A good tight braze IS stronger than steel BUT ONLY IN TENSILE STRENTH. The frame joints will see a lot of shear stress, where braze is not so 'strong'. Your joint designs would need to account for this, e..g. lots of overlapping joints / gussets and the like. And to be fair, i think your original question seemed to be about whether anyone has been through a similar design process.

Nonetheless, as many people have said, an excellent braze can out perform a poor weld, but in most cases even a mediocre weld will still be better than braze for the stresses that the frame will experince. Factor in poor fatigue life and corrosion issues too.... just my two cents.

Cumbrian Builder - Welcome to RRR! Sounds like you know your stuff. Make a proper Intro and let us alll say hello. BTW, this thread is a couple years old so hopefully the OP gave up on that foolishness.

Thanks Sam_Fear, I know its an old thread but wanted to add my proffessional opinion to the knowledge-base for whoever comes along and reads it next. I've been lurking here a while now, so i'll take your advice and introduce myself properly in the intro section....

Back in 1959-63, when I was studying to be a shop teacher I had a couple gas welding courses. We butt brazed 3/8" thick by 2" mild steel, utilizing a deep "V" groove.

In order to pass, the brazed pieces had to withstand a 180 degree bend, both a root bend and a face bend, with no evidence of separation.

That degree of strength should be sufficient for a well designed hot rod frame.

Since nobody has asked I will.

Are you talking about brazing or braze welding? These are two different things.

brazing is very strong and would hold up assuming your joint configurations were acceptable and contamanation was not an issue.

braze welding would not be recommended for chassis work.

The race cars and aircraft frames that are being reffered to are brazed, not braze welded.

What is the difference you ask?

in brazing the filler metal is flowed into the joint

brazing requires specific joint design and closely fitted joints with a particular allowance for the filler to flow in. Filler is drawn into the joint using capillary action.

in braze welding you are using a rod and applying the filler metal in quantity.

Two very different processes.

A brazed joint is very strong.

A braze welded joint is not as strong.

Please for your safety and my families do not braze weld your chassis.

I am a weld engineer with many years of experience in a variety of welding industries.

If you can braze weld then GTAW (TIG) will be easy for you. GMAW (MIG) should also be easy once you figure out how the equipment works.

By the way if you were planning on brazing and leaving the joints exposed I would not recommend it. Brazing is more susceptible to corrosion than a typical arc weld and should be coated. This is due to the fact that you are using dissimilar alloys to join the part, i.e. steel with a silver braze or bronze braze.

bob w said:

Back in 1959-63, when I was studying to be a shop teacher I had a couple gas welding courses. We butt brazed 3/8" thick by 2" mild steel, utilizing a deep "V" groove.

In order to pass, the brazed pieces had to withstand a 180 degree bend, both a root bend and a face bend, with no evidence of separation.

That degree of strength should be sufficient for a well designed hot rod frame.

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That is a good static test Bob. A bend test gives a a person and idea with regards to the eleasticity of the welded joint aka elongation.

A chassis is cyclically loaded and while the bend test offers some idea of joint soundness it does not give you any idea of how the joint will hold up under twisting, bending, vibration, etc.

To clarify, I in no way want to suggest anyone braze a hot rod frame together. With so many better options available there simply isn't any justification to do so.

While I believe it can be done and done safely it would not resemble any conventional rectangular tube frame. In the 60's and 70's some British race car frames were brazed. But those were very thin wall tubular space frame designs. The space frame design addresses the twisting and flexing issues associated with brazed joints.

So, weld on, boys.