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[Ken]

I was watching the tv programme ‘ made in britain’ last night and they featured Brompton folding bikes. When it came to brazing the tubes at the bottom bracket they did something I’ve never seen before.
I was trained to braze by ensuring a good fit between the components, heating them and allowing just enough  braze to run round the joint line.
They applied braze as you would with gas welding and steel wire building up a broad line of brass that bridged across the joint, I’d say it was about a quarter inch wide.
They obviously know what they’re doing but I’ve never seen this approach has anyone else ?

[Ian F]

I am expecting to be shot down here, but that sounds like "bronze welding" .  See the Sifbronze literature to see what they say. I understand it has been used to join tubular structures on car sub frames etc.

Ian F

[autorover1]

That was my thought when I read it. I did Sifbronze welding at School 60 yrs ago.

[Ian F]

I think I recall that Jaguar used this method on sub frames for E types and their predecessors- perhaps only initially?

Ian F

[2286]

On the auto braze they had invented they placed in a circlip style lump of rod into the joint prior to heat (hinge joint).

On the the other joint they did use filler rod as per gas welding.  I noted they pulled the torch away and kept the filler rod feed continuous not vice versa?

Most top end steel tube bikes now use tig not flame due to it accuracy.

I agree brompton weld width did seem excessive.  Also noted the lack or minimal use of flux, to etch and aid run, unless its in the rods.

[Billy]

Hello Ken,

An interesting topic that caused a lot of commotion in the late 70's/early 80's when brazing was banned on structural repairs, particularly on over lay panels such as sills and suspension strut top plates by the MOT. Brazing is considered to be an "adhesion weld". I managed a workshop at that time and we could not use oxy-acetylene welding sets due to fire regs. MIG and TIG were not around generally and arc welding was used for heavy work like chassis only. Some clown came up with the idea that you could strike an arc using two carbon rods with an arc welding unit and"weld" using special fluxed brazing spelter and called it carbon arc welding.

Cheers, Bill

[Ian F]

Thanks for that Bill. I would be interested to hear what you thought about Sifbronze and "bronze welding"?
I used it on TR bodywork in the 1970's and always believed it to be well up to the job. It didn't seem brittle like a lot of arc welding results, but you are right of course, it wasn't true welding.
I use a MIG welder now but still get out the Sifbronze occasionally for some jobs (non-professional work, only on my own vehicles and occasionally for friends etc.)

Ian F

[Billy]

Hello Ken,

Fifty odd years later and memory might have (has) faded slightly. I think I recall that Sif bronze became a generic term for brazing because "Sif" was a predominant supplier of brazing flux and actually produced pre-fluxed/coated brazing rods. Seemed a good idea for production work because it saved time and continuity by not stopping to dip the hot rod into the pot of flux. Problems I recall were: damp caused the flux to become soggy and fall off, oil contamination stopped the flux from working and if dropped,the coating fell off anyway. Brazing to me was when one could heat up two surfaces,coat with braze and clamp together or treat like soldering with tight tolerances. Bronze welding could "puddle" a larger gap. Havn't held a Saphire No 2 for years.

Cheers, Bill