String termination question

[Geoff Sykes]

Aha! This is the answer I was searching for. In fact it even did a lightbulb
routine above my head during breakfast this morning. Reading your response
just confirmed that what I had realized actually made sense.

The problem isn't that we are limited to only one axis of termination at the
agraffe/capo bar, it's the reason why we are forced into having two at the
bridge. The bearing at the agraffe/capo bar is aggressive enough to define a
positive termination point. But at the bridge we can't have that much "down"
bearing due to the fact that it would flatten out the soundboard and prevent
it from vibrating. So, with the need for lower downbearing at the bridge
adequate termination is not possible without some help. Therefore, in order
to create a definite termination at the bridge the use of two pins to put
that "S" kink, or clamp, in the string was developed. This clamping provides
a sideways bearing that's pretty much equivalent to the bearing already
present at the agraffe/capo bar. Now we have good termination, but we are
now also stuck with two axis of termination. One against the side of the pin
and one against the notch in the bridge. Hence the need to be careful that
both those axis are in alignment. 

Physics can be pretty cool sometimes. Thanks to all for the replies.

-- Geoff Sykes, Los Angeles






-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Farrell
Sent: Monday, January 14, 2008 8:04 AM
To: Pianotech List
Subject: Re: String termination question


I'll stick my neck out here and speculate on a direct answer to Geoff's 
original question of why we need a two-plane termination at the bridge and 
only one at the capo/agraffe.

Is it not because at the capo/agraffe, we can easily have as much of a 
counterbearing angle as needed to provide adequate clamping of the string to

the termination up there. However, on the bridge, the counterbearing angle 
(or backscale or downbearing angle) is restricted by soundboard performance 
needs and is usually rather small. So the small backscale simply does not 
provide for sufficient downward string force into the bridge - so we need to

provide a clamping mechanism.

In other words, the front termination is self-clamping because of the large 
force of the string on the termination point created by the string tension 
and the large counterbearing angle. The bridge termination requires a manual

clamp (offset bridge pins) of some type because of the small force of the 
string on the termination point (bridge) created by the string tension and 
the small counterbearing/backscale/downbearing angle.

And of course, there may be more reasons, but it seems to me this basic 
difference in string pressure on the termination points is reason enough to 
go to something like what we see in most pianos. Even the bridges with 
agraffes have similar needs & features.

Ron?

Terry Farrell
  ----- Original Message ----- 
  I made the mistake of thinking the other day, and I started wondering why 
piano strings are terminated at the bridge on both the X and Y axis but at 
the capo bar, or agraffe, on only the X, (or perhaps that's Y depending on 
how you are looking at it), axis. We go to lengths to make sure the strings 
are seated properly at the bridge so that there is a definite and precise 
termination in both planes at the bridge and bridge pin. Why then is the 
lack of termination in both planes not a problem at the agraffe and capo bar

end?

  -- Geoff Sykes, Los Angeles

----- Original Message -----
>> I don't think the primary purpose of a bridge pin is to prevent the
>> string from sliding around on top of the bridge.
>
> The pins serve two functions. They are the string termination, and 
> they
> clamp the string to the bridge.
SNIP
> Ron N