CA on bridge pins

[Alan Barnard]

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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