On 4/16/07 7:08 PM, "Daniel Gurnee" <dgurnee at humboldt1.com> wrote: > Fred, > > Whether there is a tendency to breakage, the is a lubricative quality of > movement between dissimilar metals and very little between identical metals. > It would be hoped that the softer metal would be the bridge pin for that where > is where one would want the wear. > > Daniel Gurnee Just to separate out this particular portion of the thread: We started with Ric suggesting a harder bridge pin might cause string breakage because of being harder than the wire (or closer to the hardness of the wire, whichever it might be). I suppose friction and wear enter into that in some degree, but I don't think there is enough movement of the string back and forth past the surface of the bridge pin to make it a significant factor. In any case, the statement was about hardness per se, not friction. But I took it a step farther, and asked why one should assume that, for example, a hardened capo would cause more string breakage than an unhardened one. I think there is a knee-jerk assumption on the part of many that this must be so. I don't get it, I don't understand what mechanism would be involved. Let's leave friction to the side - it may be greater or lesser with one or the other, but friction isn't hardness. If friction causes string breakage, that's one issue, but it is separate from saying hardness of the termination point causes breakage. I ask again, why should a harder capo, all other factors being the same (profile, angle of deflection, friction) lead to more string breakage? I believe we are talking about the type of breakage caused by work hardening of the string, by the string being hit at a point away from the termination and flexing in some fashion around a "fixed point" (yes, it is not really a point, but it is, relatively speaking, fixed), and the metal in the wire at that point becoming fatigued by repeated flexure. Since the string is being struck relatively far from the fixed point, why should the relative hardness of the point be a significant factor in how much work hardening takes place? I guess one mechanism might be the wire actually deforming (developing a "dent") against the capo, but is this likely, given the scenario: springiness of the wire, place where the wire is struck,force applied, springiness of the hammer assembly applying the force? My notion is that a harder blow simply increases the excursion of the wire, hence creating more of a bending movement at the termination point. A repeated bending movement, which eventually results in breakage. But the blow is not great enough, nor in the right place, to drive the string into the capo so as to cause it to deform (if, indeed, doing that with a felt covered wooden hammer cold possibly have that effect). I'm not really arguing one way or the other. It's just that I don't find the conceptual modeling convincing, and don't have experimental data to rely on. The anecdotal data I have heard is not convincing, as usually some other factor was involved, or might easily have been (changing the profile of the capo or the angle of deflection, manual working of the wire to level strings, etc). Regards, Fred Sturm University of New Mexico
This PTG archive page provided courtesy of Moy Piano Service, LLC