Originally Posted by
unterhausen
there is one builder that is pushing this theory hard, but the reason for butting is very simple, because the haz is weaker. So it needs to be thicker than the center of the tube. That was always the stated reason for it. I don't think that straight gauge pushes that much deflection to the end. I hate speculative engineering, particularly in cases that are not self evident and likely to submit to a good thought experiment. If someone can show me a good fea model of a frame that demonstrates this, then i would be happy. As it is, it's just speculation. And no, a diving board is not a good example.
I agree that the contact with the headset cone probably caused this.
However, I will stick by my hypothesis that if the middle is thinner, it would flex more than if it was thicker and thereby concentrate at least some flex there rather than force it all out into the next weaker area, the HAZ. I suppose I'm thinking of it like butted spokes - again, my understanding is that the butting reduces some of the stress on the nipple and bend. It seems like a fairly sound hypothesis and i'm sticking to it until someone proves me wrong with data! :-)