CA on bridge pins

[Andrew and Rebeca Anderson]

Alan,
I've seen agraffes on old Sohmer grand bridges and apparently Stuart 
uses a modified agraffe on its bridges.  As to how well this 
works...  It is credited with giving Stuart a long sustain time due 
to increased impedance, something we can achieve when necessary by 
securely fastening weights to the underside of the bridge.

Andrew

At 12:32 AM 9/24/2005, you wrote:
>Well reasoned thoughts, interesting possibilities.
>
>Now my head hurts.
>
>Has anyone, on making a new long bridge, actually epoxied in all the pins
>and tested the results?
>
>Here is another ort for thought: Since a v-bar/bearing bar/capo d'astronaut
>termination works just fine on one end of the string, why do we have pins,
>side-bearing, etc., on the other end? Oh, wait, it just came to me (Here,
>boy ...) the bridge has to move vertically. Okay, stupid question. How
>about little agraffs screwed into the bridge? Does that work?
>
>As to Tunelab and the spectrum (which is reason enough to use TL, IMO).
>Sometimes you note the weirdest things. Like two treble strings that
>individually are dead on pitch but played together are sharp or flat. This
>happened to me, today, on an interesting little nightmare spinet which I'll
>talk about another time (maybe 2:30, or 4:27, I'm not sure when).
>
>But that graph can help diagnose and/or demonstrate to the customer all
>kinds of interesting string phenomena.
>
>Hang on TX and LA! (Auntie Em, Auntie Em ...)
>
>Alan Barnard
>Salem, Missouri
>
>
> > [Original Message]
> > From: Greg Graham <grahampianos@yahoo.com>
> > To: pianotech <pianotech@ptg.org>
> > Date: 09/23/2005 11:45:43 PM
> > Subject: CA on bridge pins
> >
> > Following up on threads from earlier this summer, I
> > tried some CA on bridge pins with false beats, new and
> > old pianos, grands and verticals.
> >
> > Before using the glue, I tried just touching the tip
> > of a screwdriver to the pins, and, yes, the beat went
> > away (sort of the anti-Sonny&Cher?).  Applying the CA
> > sparingly to the pin/bridge joint stopped the beat. So
> > did gentle string seating on neighboring strings.
> > I'll have to see which lasted when I go back (though I
> > need to take much better notes for future
> > experiments).
> >
> > THEORY 1 of false beats involves the pin and notch
> > terminating the string at different effective speaking
> > lengths parallel or perpendicular to the bridge.
> > Generally, string cuts at the notch increase the
> > speaking length and lower the pitch when vibrating
> > perpendicular to the bridge.  String seating and
> > careful notching assume this is the dominant theory.
> > Could CA help this? Maybe?(see below)
> >
> > THEORY 2 suggests the pin is loose and vibrating,
> > creating the false beat.
> >
> >   Theory 2-A: I'm wondering: could this be the result
> > of adding pin mass to the vibrating string and
> > lowering pitch when moving parallel to the bridge, but
> > not when perpendicular?
> >   Theory 2-B: Is the mushy pin creating the illusion
> > of a longer string by rocking back and forth the same
> > distance the string would move if terminated a short
> > distance beyond?  Picture playing jump-rope.  Your
> > hand is the bridge pin, and your shoulder is the
> > "virtual" termination point.  Now put your wrist on a
> > table.  "Longer" string and lower pitch parallel to
> > the table, or bridge.  A very small pin movement could
> > simulate a significantly longer string.
> >
> > (Theory 3, the old "kinks or defects in the string"
> > thing, seems to have gone the way of "the Earth is
> > flat".)
> >
> > Observations and complications:  It is easy to hit the
> > pin with CA in a grand without getting any on the
> > string.  Visibility, accessibility, and gravity are
> > all favorable.  The opposite is true in a vertical.
> > Any tips for hitting the D7 pins in a vertical without
> > a couple or few drops missing the mark and running
> > under the strings on the bridge?  I missed a few
> > times, but eventually got the CA to the bridge pin,
> > cured the falseness, and seemed to not hurt anything.
> > Is CA under the string a horrendous no-no, or merely
> > an acceptable side effect with no serious
> > consequences?
> >
> > ALSO... would the CA under the string at the pin tend
> > to fill in, swell up, shore up, or otherwise improve
> > the string cuts at the notch edge, thus improving the
> > tone according to Theory 1?  An alternative to
> > seating?  Too many negatives to consider it?
> >
> > Something else to chew on:  False beating strings in
> > the high treble clearly show as two frequency peaks in
> > TuneLab's spectrum display, often several cents apart.
> >  Would a 1mm difference in speaking length in octave 7
> > create a 5 cent pitch change?  I don't have the
> > formula handy to do the math on that, but it would go
> > directly to the plausibility of either Theories 1 or
> > 2-B.
> >
> > Lastly, I did not note where resulting pure pitch of
> > any of these experiments ended up relative to the
> > upper, lower, or average of the TuneLab "twin peaks".
> > I'll have to look next time.  If it goes to the higher
> > of the "false" pitches, Theory 2-A or 2-B could be
> > possible.  If to the lower, Theory 1.
> >
> > Theoretically, that is.
> >
> > Greg Graham
> > Brodheadsville, PA
> >
> >
> >
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