Originally Posted by
Doug Fattic
A set of 3 lugs can weigh between 80 and 130 grams + -. A investment cast seat lug will include a binder bolt housing that would need to be attached to a fillet brazed or TIG welding frame. I weighed a unfiled Henry James down tube lug at 33 grams and a filed one at 22 grams.
Sometimes on bicycle forums posters will say a TIG welding frame will be lighter than a lugged frame and that is not necessarily true. It is likely the TIG frame is heavier because tubing has to be reinforced by the weld. The easiest way to do that is with an outside butted seat tube and a much heavier wall head tube. Those weigh significantly more than tubes used on a lugged frame.
Yes this is a good point about the externally butted ST and thicker HT. The external butt on Columbus STs is 40mm long and adds 1.2mm of wall. I make that 33.9g. Assuming an HT that's 160mm long and 1.2mm wall rather than 1.0 we're adding another 28.6g there resulting in a total of 62.5g.
The main triangle of TIG frame also contains about 17 inches of weld, which weighs about 10g, but idk how that would compare to the very thin but much larger area of the braze in a lugged frame.
So perhaps a TIG frame is still generally lighter than a lugged one but only by a whisker and not if you use lightweight lugs and then file them.
But what about butt length? I think in theory on a TIG frame you can use a tube with shorter butts as the heat doesn't spread that far down the tube. but I don't know if anyone does this. Reynolds and Columbus do seem to supply tubes with either around 75mm as the short butt or about 100mm.
Originally Posted by
Doug Fattic
One place where it is better to use lugs is on heat treated tubing like old Reynolds 753 or Tange Prestige. Lower temperature silver brazed lugs reduce the loss of tensile strength in the heat effected zone compared to bronze brazing. Of course Fillet Pro could be used instead or 853 tubing.
853 is also heat-treated so perhaps there would also be some benefit. It's confusing because it's also "air-hardening" so in some ways benefits from heat. But you can still presumably also lose the heat treatment.