tuning stability

[Richard Moody]

Here is another take on not about seating strings so much, rather as how
bearing affects the seating of strings. 
	Bearing is how much the strings push down on the bridge.  To accomplish
this think of how much the bridge should push UP on the strings. The
string without a bridge would occupy a straight line from the hitch pin to
the upper bearing point.  In order for the string to be amplified through
a soundboard, a bridge is needed. this bridge forces the string away from
its straight line so that contact can take place.  
	Now in most stringed instruments the point of contact of the bridge with
the string is just that..a point.  In a piano  however, there are TWO
points of contact with the bridge. This can be refered to as the front
bearing and the rear bearing on the bridge.  This can be visualized by
imagining how the bridge surface between the front and rear  bridge pins
contacts the string. Now you can see if this contact is not ideal, tapping
the string to make contact can only be temporary.  
	How can the contact not be "perfect"?  Imagine the bridge rising to meet
the string as an elevator.  There is the shorter string segment from the
rear of the bridge and the longer segment from the front of the bridge.
What then is the ideal plane of the bridge surface to the angle of
deflection of the string?  If this "ideal" relationship has been met by
the piano maker, no tapping is necessary. The pressure of the string on
the bridge will seat the string properly.  If the surface of the bridge is
canted away from the string, too far either way, you will be tapping
forever, in order to "seat the string" in order to reduce false beats or
tuning instability. 
	Even if the string is seated "properly", there is a debate about whether
more down bearing should be at the rear of the bridge or at the front of
the bridge. And engineers who argue that this is impossible to worry
about, (measure) because the tolerences are too small. But don't tell that
to the people who favor rear duplex systems, or the "accujust" hitch pin.
And there is also the concept that induced strain on a sound board
"amplifies" the sound.... 

In regards to tapping strings to the bridge with a hammer shank or brass
rod, I prefer a toothbrush handle.  It seems to give a better sonic
response, in additon to the concerns mentioned below by N Barret, and R
Jolly.   I have done this so rarely, because of considerations mentioned
above, I wonder if others might want to comment about the sonic
differences between wood, brass, or plastic tappers? 
Richard Moody   
4-11-98
----------
> From: Norman Barrett <barre46@ibm.net>
> To: pianotech@ptg.org
> Subject: Re: tuning stability
> Date: Sunday, May 10, 1998 10:41 PM
> 
> Hello list,
> Let me post my 2 cents worth about seating the strings. The tool that I
made to
> do this job is a piece of 1/4" brass rod about 5" long. One end I have
filed a
> grove in to help keep it on the string. This tool fits nicely in the
> combination handle and I can just lightly bump each string down with the
heel
> of my hand. You could probably do the job by simply pushing down gently
because
> the only thing holding the string off the bridge is friction against the
bridge
> pin. This is my humble opinion.
> Norm Barrett
> 
> Roger Jolly wrote:
> 
> > Hi Jerry,
> >          The reason I prefer a hammer shank, is that it will split
before
> > you can kink the wire, ( another scorce of false beats) also less
chance of
> > indenting the bridge.
> 
>