Question about old Italian ti welding practices
 

I'm wondering if anyone can tell me about early 80s titanium frame construction, and specifically about the joints on Trecia (and to a lesser extent, early Passoni) bikes? I only found out about the existence of Trecia bikes and Amelio Riva recently, and was immediately struck by the incredibly smooth tt-st joints in particular. They almost look fillet brazed. Were they just formed through multiple passes and a lot of filing, sort of like old Cannondale or Klein aluminum welds? From what little I have gleaned about ti construction, it seems like that would be difficult to pull off well.

Full disclosure: I'm not a frame builder (yet) and have only just started trying to familiarize myself with all the concepts and terminology, so apologies if this is boringly obvious for folks here. For whatever reason I've been having a hell of a time finding anything about the specifics of 70s/80s ti welding practices, in any industry.

Thanks!

Not obvious at all! This is the first time I've heard of them and I've never welded Ti, but searching for them on Google, yes it looks welded and filed down to me. I guess as on those early Cannondales people weren't ready for the look of an unfiled weld at the time. We've got much more used to them now. Maybe also their welds didn't look that great before they filed them... I've noticed on some Al bikes the welds seem to be filed in a couple of spots only, perhaps because that's where they looked a bit lumpy!

That all makes sense! I guess the thing that really stands out to me about the welds is less the filing and more the size or volume of the weld joint itself. Maybe it's just an optical illusion (they are skinny tubes), but it looks to me like the material deposition at the weld on those old frames is WAY greater than on virtually all modern stuff. I don't know if that would be the result of a greater number of passes or if you can just create a very large puddle on a single pass? And then, theoretically, what would be the mechanical consequences of doing it that way?

A Cannondale shop I worked in had a Caad8 frame cut away showing off the welds and tube butts. The welds on that frame were double pass as was clearly seen, which surprises me as I always thought that a weld on top of a weld was seamless.

Yes agree they look like they must have started our pretty chunky! The initial size of the bead is related to the thickness of the metal quite a bit and Ti tubes will be thicker than steel ones. But modern Ti bikes usually have smaller welds than those look like they were I agree. Perhaps on these older frames the Ti was thicker wall than what we use now.

You can shove a bit more material in on the first pass but only up to a point. I reckon they probably did a second pass with lots of buildup with the intention of filing it down. Idk what that does on Ti but on steel you would be worried about distortion and weakening the metal from overheating.

On Ti it's quite common (nowadays) for some reason to do a first "fusion" pass (which means not using any filler rod) and then a second pass with filler over the top.

One of the big Ti brands used to do a cosmetic weld pass.

Ah yeah that's helpful, thanks! I just found a 1974 Bike World Magazine review of Speedwell, Flema, Teledyne titanium frames, and it seems like figuring out the appropriate level of stiffness was a little hit-or-miss for the early fabricators. Considering that the Trecia bikes were supposed to ride pretty well without using particularly oversized tubing, I think it's safe to infer that the tubes were rather thick (by today's standards).

Yes I should think getting on for 2mm as Ti is about half the stiffness of steel so you'd need to double the wall if you don't change the diameter. It's possible Ti alloys weren't as strong back then as they are now. If you need 2mm to get the strength you will have the stiffness you need without going oversize. Or maybe they couldn't draw them as thin. Ti has some strange properties and is a bit of a beast if you try to bend it or do anything with it. But Reynolds seem to able to double-butt it now!

The Ti alloys used for tubing now are similar strength to CrMo but half the stiffness. CrMo is about 800MPa strength and 200GPa stiffness. Reynolds 3AL-2.5V Ti is 900MPa and 115GPa. So you go oversize. The tubes they sell are 0.9mm at the ends (vs about 0.8mm for a typical quality CrMo tube) with diameters from 31.75mm to 44.2. A typical steel bike would be 25.4 on the TT (or maybe 28.6) and then either 28.6 or 31.8 on the DT.

The Reynolds Ti tubes are pretty expensive (about 7-8x the price of quality CrMo) but cheaper bikes probably use 0.9mm plain gauge. I saw a video about Moots bikes I think it was and they had a big rack of about 8m long Ti tubes they were just cutting up so they must have been plain gauge.

That's great info, thanks! The only confirmed figures on tube diameter and thickness I can find are for the mid-seventies US made Teledyne Titan, which used grade 3 Commercially Pure titanium, straight-gauge, 1 1/8" and 1 1/4" for the top and down tubes, with most of the tubes being 0.8 or 0.9 mm thick. Teledyne reported that they went with CP because they ran into problems with work hardening on the alloys they had access to. Apparently, those frame figures worked pretty well, reviewers tended to describe the ride as forgiving but not too soft or dead. Interestingly though, the welds on the titan are pretty small and "modern" looking, so the giant welds on some of the Euro bikes probably were just aesthetic.

Interesting. Pure Ti has a much lower strength. Grade 3 is 450MPa (https://www.sciencedirect.com/topics...itanium-alloys) compared to 800MPa or so for a quality CrMo or similar tube. But I guess you'll get away with it in 0.9, and people were accepting of more sketchiness in the 70s. They used to use Reynolds 531 (a bit weaker than modern CrMo so long as you don't weld it) down to crazy thin gauges.