capo-hardening/string breakage

[Fred Sturm]

Richard,
	I'm just not really convinced that hardness per se is an issue for
string breakage (at least within normal parameters: hard enough not to
deform too much over time, probably softer than the wire itself - though
even here I'm not entirely convinced). Seems to me this might be one of
those areas where we assume we know something and then never bother to
question it.
	Breakage of a string at the capo happens mostly from an action similar
to kinking and rekinking a wire. THe bend is accentuated when the string
is struck, then springs back beyond rest point - and back and forth
during vibration. As long as the fulcrum (capo) is stable and firm -
that is, it doesn't move significantly realtive to the string, and
doesn't have "springiness" - why does it make a difference exactly how
hard it is? 
	I don't think the wire is deformed in cross section ("smashed") by
hammer blows. In the first place, the hammer blows occur away from the
point where the wire crosses the capo. In the second place, the hammer
surface is springy. If it were a matter of deforming/thinning the wire
during impact, hardness of the capo would matter. But I don't think the
mechanics are set up in a way that would make this a factor.
	Sharpness of radius and high angle of deflection are very definite
factors in breakage, no question. I just raise the question whether
hardness per se, other factors being equal, has actually been shown to
have a significant impact. Preferably experimentally. Can anyone point
me to experimental data? Or offer a mechanical engineering explanation?
	No question that much work has been concentrated on this area of piano
design. THis is the area pianists need to make "sing," to bring out
above the rest of the piano. Hence duplexes, aliquots, unequal unison
lengths, varying angles of deflection, etc, etc. Hardness/softness, as
far as I have been able to determine has mostly been an issue of
maintaining a clean termination over time. That is, at least, how I have
always viewed it.
Fred Sturm
University of New Mexico

Richard Brekne wrote:
> 
> Fred Sturm wrote:
> 
> > There seems to be some concern that a too-hard capo causes string
> > breakage. Is there real, solid evidence for this? Not just anecdotal
> > stuff.
> 
> Sure there is, and thats one of the (several) reasons there has been so many
> different arrangements tried out over the years
> 
> One way of looking at this all is like this.... If the condition of the
> termination point is such that it is hard enough, sharp enough, and the tension
> of the string is high enough, and the deflection of the string away from the
> termination point is high enough.... the string will break.  
> ----------(snip)
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no