[CAUT] Hardness of termination vs string breakage (was Re: restrung D)

[Ted Sambell]

With all due respect. I had an experience several years ago with a 
Bosendorfer grand which seems to contradict this. It continually broke 
strings in the top section. Bosendorfer, and I believe Petrof have retained 
a feature found in early 19th. century pianos such as Streicher and Erard, 
namely, a removable treble capo bar. I removed this and found it to have a 
very sharp edge, and to be badly grooved, the edges of the grooves still as 
sharp as the unworn arears. The metal was quite soft , so I was able to 
easily reshape it to the radius resembling that of a 2.5mm rod, and polish 
it. I then re-strung the section  (actually the two top sections) and there 
has never been a broken string since over many years. The piano is used 
quite heavily by good pianists. Moreover, if anything, the tone was better 
than before. A vibrating string is quite evidently being stretched at 
amplitude . and the consequent lengthening is offset by the alternating 
termination point caused by the deflection of the wire around the radius of 
the bar. As is said, the proof of the pudding is in the eating.

Ted Sambell---- Original Message ----- 
From: "RicB" <ricb at pianostemmer.no>
To: <caut at ptg.org>
Sent: Thursday, April 19, 2007 3:00 AM
Subject: [CAUT] Hardness of termination vs string breakage (was Re: restrung 
D)


>
> It is a matter of all these things, including hardness. Really, this kind 
> of goes without saying.  A soft sharp profile will wear and groove, and it 
> will do so in a way that works out nicely over time.  A rounded soft 
> profile on the other hand will buzz like crazy with wear.  Dig out 
> McMorrows book for some good perspectives on it.
>
> Fred,  there is friction at the bridge pin from something... this is 
> obvious because of the pins getting damaged over time. If the metal of the 
> pin was significantly harder then the string... these same moments would 
> still be at work and the wear and tear would be transfered to the string 
> material.
> I mean... why would we have any use for super hard abrasives like diamond 
> files or any such thing unless the basic idea that harder vs softer 
> results in softer loosing ?
>
> Cheers
> RicB
>
>
>    On 4/17/07 8:36 PM, "Keith Roberts" <keithspiano at gmail.com> wrote:
>
>     > Hi Fred, strings breaking at the capo bar I think it would be a
>    matter of
>     > bearing length, the sharper profile capo bar having less bearing
>    length and
>     > the softer capo bar developing a  longer bearing surface no
>    matter what the
>     > profile. All the pressure and force of a FFF blow concentrated
>    over a shorter
>     > bearing surface and segment of wire has far more potential to
>    break a string.
>     > > Keith Roberts
>
>    Yep, I agree. Sharpness of profile plus angle of deflection. I don¹t
>    think
>    hardness enters into it, unless somebody can show me how. I don¹t
>    see how
>    softer metal would make a sharp profile with a high angle less apt
>    to string
>    breakage. Maybe it does, but I don¹t understand how.
>    Regards,
>    Fred Sturm
>    University of New Mexico
>    --