I've heard from multiple sources over the years that Passoni tubes were all rolled from sheet and welded along the seam. Maybe each source was quoting the other one and it all started from a misunderstanding? Possible I guess, but I'm inclined to believe it's actually true. That dude was nuts (or maybe still is?)

Probably similar to how all Ti frames are welded, in the atmosphere with an argon purge inside, and a really good gas lens on the welding torch. It's not really that hard.

Having done both, I do see a strong resemblance between Ti welding and fillet-brazing of steel. Hard to explain but basically the behavior of the molten puddle. The Ti puddle acts more like a brass ("bronze") fillet's puddle than like a steel TIG weld. I friggin LOVE the molten Ti puddle, it's one of the most beautiful things I've ever seen. Fillet brazing is pretty cool too, but nothing beats Ti for me, while I'm actually doing it. (For riding, it's a toss-up. Other factors are more important than what material it's made of)

<brag> when I took Gary Helfrich's UBI class (early-'90s), my very first test weld in Ti, less than an inch long, came out awesome. It looked just like a Merlin/Seven/Moots/whatever. </brag>
Gary was surprised at first — it was literally the first time I had tried welding Ti, and I wasn't even a good TIG welder in steel, I was a TIG beginner. But then he remembered that most of the people he'd taught who'd picked it up the fastest were brass fillet brazers. The ones who were the worst at Ti were guys who were experts at welding aluminum, which is so different that all your reflexes are wrong! Un-learning wrong reflexes is hard. But even TIGging steel doesn't prepare you for TIGging Ti as well as brass fillet brazing on steel does.

Gary also taught us how to smooth the welds, like on a Passoni. I signed up for his class after seeing a 1.0 kg Ti frame he made and brought to the Interbike show, it was fantastic. It looked so organic with the tubes just flowing into each other. I didn't make a whole frame in the class — you didn't build a frame in that first class of his, though the class changed, and later editions you did build a frame. But in this class of maybe eight? guys, I was the only one who made something rideable, a Ti stem in the style of an Arctos or Ibis, welds all smoothed and polished. Came out truly excellent. (Gary also taught Ibis how to make stems, so the family resemblance between an Arctos and an Ibis is no coincidence.)

Suffice it to say, the equipment needed was pretty minimal, and I went back to Davidson after the class and started making Ti frames there after collecting a pretty minimal set of Ti-specific tools. Mostly just some purge fittings to go in the openings of the frame, a couple small purge boxes for things like stay-end "bullets", and the argon plumbing to those fittings. And a really big gas lens for the TIG torch. Making Ti frames is easy!

Too bad they're totally obsolete these days. If it ain't carbon, it's worthless, right?

Mark B