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
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