Framebuilders - double butted vs triple butted etc...

I have recently been looking at steel frames and see a lot of "double butted" "triple butted" labels but haven't got a clue what they really mean. Mostly these are low end cromoly frames on production bikes, so this is probably the wrong place to ask, but I figured you guys would know the answer.

"A single butted tube is thicker at one end; double butted tubes are thicker at both ends (each end of the same thickness); triple butted tubes have ends of unequal thickness; and quadruple butted tubes have ends and midsections of varying thickness."

snipped from: http://www.desperadocycles.com/The_Lowdown_On_Tubing/About_Steel_Tubing_page3.htm

I've noticed that some builders use both lugged construction and double-butted tubes. Isn't that wasteful or at least pointless?

I've noticed that some builders use both lugged construction and double-butted tubes. Isn't that wasteful or at least pointless?

The lug is just a joining method and does not support the load the tube carries. Regarding lugs and butts, I like to have the full length of the lug fit on the butted length of the tube. Some of the newer tubesets have such short butts that this is hard to achieve if you are building a small frame.

I have read of some builders choosing butts at other than the end sections as reinforcement for S&S couplers, in a way, butting each end of each segment of the separable tubes. I have also heard of some builders also heat-treating these separable tubes to add strength.

That would be nice, but you can't get a tube short enough to use uncut in S&S couplers. It may work in horizontal top tubes over 600mm, but I doubt it would work in anything else.

Generally what it means is using beefier tubes so even if you are interrupting the butts, mechanically you have enough material to work with anyway.

As for butted tubes being pointless in lugged construction, theoretically you're right, Katzenjammer. In a perfect world you could use say .5 or .6mm straight guage tubes in a lugged frame IF the lugs were designed to do so.
However, lugs in their current incarnation are designed to look pretty and act as a conduit for the brazing material and aren't designed specifically as a piece of mechanical reinforcement for the frame.

"However, lugs in their current incarnation are designed to look pretty and act as a conduit for the brazing material and aren't designed specifically as a piece of mechanical reinforcement for the frame."

Uff, and here I've been taking the "lugged steel is best" propaganda at face value, assuming that lugs are both joint and external butting rolled into one, as it were. Another illusion shattered. Bummer. :( Thanks for clarifying.