Hi Fred
When you first put the question so firmly, I must admit I do not
<<know>> for sure that a harder capo (or by same reasoning bridge pin)
would cause string breakage. I have always heard it so, and the reason
given has always made sense to me.... tho I am eager to hear the ensuing
discussion here. The reason as I understand it rather forces one to
include friction... and I suppose things like trackage... or at least
whatever moments are involved in what eventually causes wear and tear.
You make the point that there is little or no movement at the bridge
pin, hence you discard the friction moment and look at hardness alone.
How then do nicks occur in bridge pins in the first place ? I guess my
point is that /whatever/ causes these knicks and grooves would tend to
cause them in the string instead if the pin was significantly harder
then the string.
As for whether or not hardened capos (all else being equal) will result
in a greater propensity to string breakage then less hardened... I have
no hard data to show this either... when you first mention it. Perhaps
this is just one more of those things we hear, sounds sensable, and
accept as truth without further ado... or perhaps it really is so. I do
know that when I have reshaped capos that have softer iron (determined
as per McMorrows <<how it feels to the file>> method) I go for a very
sharp and V shaped profile and when I am dealing with hardened iron I
opt for a wider and more U shape. Early experience with going with thin
and V shaped regardless did seem to associate hardened capos with more
string breakage. But to be honest... I did no formal accounting to be sure.
Looking forward to hearing other thoughts on this bit.
Cheers
RicB
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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