Dave:
I directed my post to Steve.
My only point was that joints don't "move" internally after brazing unless they fail. The tubes flex (during normal use) or yield (during cold setting). Yes buckling is extreme, but it happens. Think front-end impacts....
There's nothing inherently wrong with a little cold-setting; people re-space rear triangles all the time from 126 to 130 or whatever.
In steels, you have elastic behavior (returns to original shape after the load is removed), plastic behavior (doesn't return to original shape after the load is removed), and breakage (fails/separates completely). If you have have plastic behavior, you've yielded. The next thing you will experience if you keep increasing the load is UTS (ultimate tensile strength), where the material fails. Yield is not a failure. It's certainly something you want to control (like via cold-setting), but it isn't failure. In a bike frame, you don't yield the material in normal use. That is why steel frames don't "go soft" or any of that other marketing/mythical BS. A twenty-year-old steel frame will perform the same in terms of stiffness as a new one (I'm assuming it hasn't rusted out from the inside, i.e, the material dimensions must remain the same - generally a pretty safe assumption with a bike frame). (Overheating and the subsequent embrittlement of the steel that can lead to failure is a whole different topic...).
Steel must yield for a frame to cold set. Otherwise, it would just return to its original position / shape, a la 753. 753 has a significantly higher yield strength than 531 or Columbus SL/SP or whatever else that's non-heat-treated steel. A little intentional localized yielding is not a failure in steel....
Cheers and Material Science is your friend,
Greg Parker A2 MI USA
In a message dated 7/1/02 6:57:42 PM Eastern Daylight Time, DAVIDTESCH@aol.com writes:
> In a message dated 7/1/02 3:38:45 PM Pacific Daylight Time, GPVB1@cs.com
> writes:
>
>
> >>
>> > experience. A frame with minimal yield strength on the table, has soft
>> > joints
>> >
>
> Actually those were Steve's observations, Yes a dead frame on the table is
> a dead frame on the road. But remember the table gives you tremendous
> advantage to moving the frame, that you would never have riding it.
> GPVB1 made an observation about setting, but an extreme one. If you
> "buckle" a tube trying to set it, then you have started with something that
> is off a country mile. I always kept my mains at +-.005 in all tests.
> Once you become accustomed to doing that, it is not difficult to maintain
> +-.5MM as was, and probably still is industry standard. Lot of myth
> involved with coldsetting, as long as a frame is not too far out, it is no
> problem. Remember that during brazing, the metal shrinks anyway. The term
> "Yield" is an extreme one by my definition, as yielding is failure, like a
> kink, or a crack. You have the elastic range, and the plastic range, then
> you have yield. Reasonable setting is nothing more than very slight plastic
> deformation. An extreme example would be 753, lots of elasticity, loads of
> it. You could deflect a 753 tube till it touches the table, and have it
> spring back within a couple thou. If you built a crooked frame out of 753,
> you have built a crooked frame, period.
> Dave Tesch