calstar 

So.... no harm to the haz, blades still fine? These builders(RIH) had a run of 80yrs +-, bikes ridden to world championships, obviously the quality was there, anyone bending blades like this? Probably heat treated blades wouldn't work(I guess) because the steel would be annealed/softened, right?

thanks, Brian

JohnDThompson 

Can't argue with success.

I bend the blades cold, FWIW.

MassiveD

I don't see the point in hot bending blades when they can be cold bent. It isn't more efficient. Looks as though someone knocked up an jig that worked, and they never changed their process.

As far as the HAZ BS is concerned, you are going to heat the tips of the fork to braze on the drop outs, so fair bet the steel was chosen with that in mind.

While the end of the fork blade is a thin tube of steel, it is essentially the same weight of material as you see in the upper part of the blade, just thicker walls. No question you can burn off a few microns of metal with a hot flame, but the section in the walls of the fork tip is pretty much the thickest in tubes in the bike.

The same is true with hardened steels. Though there is some complexity there. Some of the steels are very resistant to high heat, some air harden on cooling, and some would do something similar to either annealing, or setting depending on how quickly they cool. Overall, just more nonsense to concern oneself with.

My observation having pushed through a lot of different activities with metal is that if a metal craft doesn't involved the craftsman actually heat treating metals to some sort of specification, there is often a lot of bogus misinformation about what the effects of heat are. In the case of framebuilding, in the past in particular, this also got caught up in marketing where processes like silver and brass brazing were compared to each other and welding, and a lot of bogus claims made.

Cynikal 

I'm more concerned that he is only heating one side of the blade. I would think the uneven heat would complicate the alignment.

calstar 

This is primarily why I posted, I was wondering how much strength/integrity steel loses when taken to high temps, seemingly higher than most frame builders work. There are vids showing highly respected Japanese and Italian builders
that look as though they work with temps pretty dang hot with apparently no bad results. I'm asking not so I can try to build like them, but to better understand the limits of the brazing/welding processes(without diving into technical metallurgy).

Anyhow, thanks for the input guys,

Brian

Andrew R Stewart 

Brian- I've always felt that the evenness of the temps within the joint is very important. I've read that the time spent at the brazing temp is also a big factor in how much material characteristics possibly change.


When you see the production pros with big torches/flames I see the "power" to bring the joint up to the right temp to do the brazing quickly, not to get the joint any hotter then needed. But the balance between joint temp, it's evenness of that temp, and the time it takes to do the actual brazing is where skill shows.


As to the vid... there are more then one way to build a frame. Some that we wish we could afford and some that we wish to avoid. When I saw this a few years ago I had my moment of disbelief. Andy