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Twin cylinder special

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Bryanj:
Brazing was frequently used for body repairs before small mig welders came in as the only other way was oxy acetalyne gas welding which was at a lot higher temp and could distortpanels.

VOSA  decreed brazing was not a suitablr strength panel repair as brass on steel combined with salt water created a galvanitic reaction causing corrosion away from the joint

K2-K6:

--- Quote from: taysidedragon on March 26, 2025, 05:22:49 PM ---Nigel, there is a difference between brazing and bronze welding, although they are often referred to as being the same.
The main difference in the processes is the temperature.
Brazing is carried out at a lower temp and the brazing rod flows into the joint through capilliary action.
Bronze welding is done at a higher temp and melts the filler rod and parent metals together.

--- End quote ---


Unsure of where the information comes from?  as not in my experience.

My father taught welding, I've oxy acetylene experience from about 12, not that this makes me expert  :) but formal training covered much more depth in as much as we carried out various brazing and welding work pieces, to then section them, reface thee cross section to then be polished, finally to acid etch that surface to display internal structure, inclusion, granularity etc in metallurgical lab. It was good insight.

Brazing, on bicycle frame of lug type is like plumbing in sweating the melted braze down via capillary, yes.

Welding is melting the  base material together, we had to practice without filler rod to understand it.

Bronze "welding " as I understand that, and it may be turn of phrase difference, is effectively making fillet with the filler rod and classically what you'd see on a bespoke frame made as such. It doesn't involve heat at the level that will melt steel (we're talking about ferrous pipes here) the pipes and brackets tailored in specific joint shape, then with a torch you'd heat the base metal to level locally, introduce the bronze while facing the flame blue tip onto that in getting it to flow, then as you move along the joint you "play" the pool of molten bronze in getting it finished as you want it, giving those classic "fishscale " linked plates as you move along, all the time monitoring how the melt is setting to give smooth integration and flow in it's junction with the steel base. No finishing required.

Most importantly though, if you start with a section of T45 cold drawn solid seamless (in that relm of this frame on here), then bring another piece in at an angle to that "birds mouthed " to fit, brazing preserves the integrity of that principle continuous pipe route as you very specifically don't take the steel past its melt point to leave the latent properties alone. The finished structure, if brazed with something like Sif bronze rod (raised silicone content) matches the spec of the pipe. Under tensile and bending load, the whole assembly is balanced in it's elasticity, not needing stress relief to hold the designed rating of materials.
Welding on the other hand, ultimately changes the base structure by melting it and then back to solid. Its a different consideration in joint design, often needing breaks in weld line to prevent stress failure propagation fully along the weld site to give structural failure under duress.

The two are fundamentally different.  One doesn't cross into the other as far as I was taught.

This very interesting frame is obviously marginal as he points out because it fractured, on what looks like straight sections. The brazing appears to be in tact.
The added panel and its welding are particularly gash though. It should at least be stich welded to prevent continuous fracture risk. Better still the panel would have relief pocket along the edge to not weld there,  with radius corners that would mitigate stress pull to then crack diagonally across the plate.

Seems a shame to have such poor welding on display of such an innovative frame designer's work.

Laverda Dave:
Interesting video and history. What a shame he didn’t start it up with those megaphones though!
Laverda utilised the spaceframe concept very successfully on their works triples for endurance racing in the 1970’s.

K2-K6:
Yes it would be interesting to hear it, looks though to be currently not running after being displayed up on the wall, without drive train too.

Reminds me also of Moulton Bicycle as originally designed in similar way, of that era too.

It would probably make more sense if he were to get another made to replace that frame if it was to be run more on track though. Looks to be toward the end of its trust equation to be sitting on it.

Laverda Dave:

--- Quote from: K2-K6 on March 27, 2025, 10:27:44 AM ---Yes it would be interesting to hear it, looks though to be currently not running after being displayed up on the wall, without drive train too.

Reminds me also of Moulton Bicycle as originally designed in similar way, of that era too.

It would probably make more sense if he were to get another made to replace that frame if it was to be run more on track though. Looks to be toward the end of its trust equation to be sitting on it.

--- End quote ---

As he says in the video Nigel, if you were to sit on it without the engine being a stressed member the frame would break :o

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