Originally Posted by bulgie

OK good to know that it's actually a thing. Still, since I've never seen it, in 50 years of studying lightweights, 20 years of that as a custom framebuilder who also did repairs on all brands, I'm thinking it qualifies as rare.

I have also never seen a steel frame crack at the shifter boss, that I can remember anyway. Seen a couple that kinked (buckled) there, from a crash or running into the garage on the car roof, but no fatigue cracks that I can recall. Gotta be way rare.

I did hear about some Ti frames that broke there, and saw one with my own eye, but I assume that was due to not argon-purging the inside enough while they welded those. Can't prove it, but I did a fair number of repairs on Ti frames, including replacing cracked tubes but more often just retrofitting them with S&S couplers. Either way, when we got to see the inside, there were often at least moderate amounts of evidence of insufficient purge. They can clean it off the outside, but I got to see where the sun don't shine, and I could tell ya some stories! Big famous brands. They were just trying to make a living in a tough business, but rushing the weld before the insides are fully purged is, in my opionion, the most likely cause of those cracks at the shifter boss. Since those are so far from the sites of highest stress, cracks pretty much have to be from improper welding, and failure to purge is practically the only thing you can do wrong there. Assuming you're good enough to stick the main tubes together anyway, a reasonably safe bet with the big-name brands. The shifter boss is much easier, much less chance of screwing it up — any other way than by not purging.

There's nothing equivalent to that in brazed steel frames. The H2O and shifter bosses are easily silver brazed in a couple seconds, doing very little metallurgical damage, and that's a task that you can teach an apprentice to do and have him doing an adequate job by the end of day after a few test runs on scrap tubing. It's so easy to braze those that I almost never see one that's not thoroughly brazed. On better quality lightweights anyway; we're not talking about frames from big-box stores here, are we? (I should look at those tests again, it's been years...)

Originally Posted by martl

The cracked shifter boss area (was in spiral shape) came up in Usenet days, i dont think the pic is still in the long term memory of the internet It was a frame by a well regarded one-man artisan framebuilder (Hagen Wechsel iirc). Another member, a well-known amateur racer from Vienna by the name of Lui Frimmel, reported he had literally a De Rosas BB fall off the frame at the start to a Hill TT sprint*), so i guess crazy stuff can happen

*) see Clarke and Dawe - The Front Fell Off (youtube.com)

Originally Posted by Bad Lag

It is referred to as notch sensitivity - the notch being a damage site that will both weaken the item and reduce its fatigue life.