Do you use a gas lens? If no, have you tried one and decided against it? I couldn't imagine going back after using one.

It's a must with Ti, but pretty useful for steel too. I welded more Ti than steel, and only really welded steel frames after I was already doing Ti, so I just used the same torch and the same gas lens for steel, and I liked it. I'd recommend the "large" lens and big cup to match, then you can get away with shocking amounts of stickout.

For those who don't know, a gas lens makes the argon flow laminar, which means no turbulence. The turbulence you get without a lens sucks in air from the surroundings. This video from Miller shows it pretty well: Notice how the length of the laminar flow region gets shorter as the gas flow (cfh) goes up, which can be counter-intuitive. So if you're getting air coloring your weld, it can help to turn the argon flow down. Note also how the length of the laminar flow region goes up as the cup size (diameter and length) go up, so try the biggest cup you think you can fit in there..

Even with the lens, there were still places where I'd build a foil dam for Ti, but under the DT/HT joint wasn't one of them. The lens seemed adequate to me for that spot, even with Ti. I also welded with a plug ("heat sink") in the end of the HT, but that was more for back-purging, not really a heat-sink per se. Same as with the gas lens, I started doing that plug and back-purge thing for Ti, and just kept doing it the same way for steel because I liked the results.

Past-tense because I haven't welded a bike in over 20 years, so my advice is old and maybe obsolete.

Mark B in Seattle