Richard wrote:

Weight is an issue. I want it to be light but at the same time be
strong
enough to do a half or full ironman. 56 miles/112 miles.

I appreciate it!

sci.engr.joining.welding would be the better ng for this.

As far as projects go, my understanding is that unless you will be
hacking
together black plumbing pipe and couplings, a bicycle frame is
probably one
of THE most difficult welding projects to tackle -- a deceptively
difficult
project all the way around, incl. fixturing.

The custom shop I visited used very high end dedicated tig, one brand
being
Thermal Dynamics, and one other, something-arc (not lincoln or miller).
Fishmouthed thinwall tubing joints are not the easiest welds, a lot of
machine control is required. He showed me an innocuous small bundle of
tubing for his next build, a ridiculous price tag for a few feet of
tubing,
iirc on the order of $500. Whatever it was made me gag.

Custom frames (the frame alone) start at $3K, and go up to $10K,
mebbe more.
I assume there is good reason for this, but I'll spend only $19.99 on
running shoes, so I'm not exactly on the same wavelength as this
crowd.
I know they get the frame custom fitted for their body dimensions, a big
time consuming deal unto itself for pro's. I assume there is a
rec.cycling
ng you could post to, to get some idea of their bike requirements.


You forgot to mention the use of stretched tubing to reduce weight.
the ends are still full thickness for braizing(!), but the middle
section can be as much as half the wall thickness.


Butted tubing. The tubing has a mandrel inserted and is then drawn
through a die to squeeze the tube onto the mandrel to form the butted
tube, the clever bit is the process to get the mandrel back out.