Crawlin' up, flyin' down
Join Date: Jan 2006
Location: Democratic Peoples' Republic of Berkeley
Bikes: 1967 Paramount, 1982-ish Ron Cooper,1986 De Rosa Professional, 1978 Eisentraut "A," 1961 BianchiCompetizione, 1994 Trek 520, 199? Burley Bossa Nova, early-1970s Cinelli Speciale Corsa
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With TIG welding, it pretty much is "the done thing" these days. But until fairly recently, the thinness of the walls of the tubes that went into top-notch frames meant that the heat from welding reduced the strength of the steel at the joints by too much for safety. Hence lower-temperature brazing, using brass on many good frame and silver (lower temps yet, but much expensive than brass, and often inaccurately called "silver soldering") on the best.
Oh, and if you see a lugless high-zoot frame from the 1970's made of Reynolds or Columbus tubes (or Ishiwata, or Super Vitus), I would bet the ranch that it was brazed without lugs and not welded.
In order to weld instead of braze, you had to do one of two things: thicken the walls of the tubes of the existing steels, or develop new steels that can take the higher heat of welding and still be really thin-walled. Both have been done. The old Schwinn Varsity's and Continentals are examples of thicker tubing walls - and they have the seriously increased weight to prove it. More recently, Reynolds, True Temper and others developed steel alloys that can take much higher temperatures than the previous top-of-the-line steel tubes as well as being much stronger, allowing for even thinner tube walls and even less weight. (Keep in mind that Reynolds 531 is/was 1930's technology - it was used in British Spitfire fighters in WWII.) The development of these new steel alloys is why high-end TIG-welded steel frames can exist at all, and it's why their advent has been comparitively recent.
Of course, there are some folks out there (hello, Rivendell) who believe that even the heat-treated steel tubes like Reynolds 853 should be brazed instead of welded. Aesthetically, I agree. As far as metalurigal properties, this is where I get off and leave it to the rest of you to fight out.
"I'm in shape -- round is a shape." Andy Rooney