Strings riding up (was Tuning stability)

[David Skolnik]

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David L -

I didn't see your post before I sent mine.   Here are my problems, which 
may already be familiar to you from the pianotech forum:


At 08:20 AM 4/1/2004 -0800, you wrote:
>I think the question that first needs to be asked is why do you need to 
>tap the strings.

We seem to be asking the same question, but we're not.  You're asking "why 
the STRINGS?".  I'm asking "why does the string need to  contact  the front 
edge of the bridge?"  What degree of departure from perfect create what 
perceptible, observable effects?

>  The assumption is that the strings ride up on the bridge pins.  Assuming 
> positive bearing and proper bridge pin angles with a bridge and pins in 
> pristine condition that is not likely.

Most of these discussions make these assumptions, or that any evident 
negative front bearing is due to overly aggressive tapping.  In my 
experience, these are not self evident. Negative front bearing can exist 
(with positive net) from relatively early in the life of a piano, due to 
errors in manufacture, bridge roll, or other conditions inducing severe 
compression.

>  The reason tapping down seems to make a difference, however, is 
> important to examine.   Over time, the strings cut into the bridge pins 
> creating a small indentation or notch in the side of the pin that the 
> string tends to want to ride in.

I'm OK with this conception.

>At the same time, compression on the bridge top (exacerbated by tapping 
>down on the strings) lowers the contact point on the bridge.

Assuming enough downbearing ( at some point in time) to compress the wood 
fibers, I would place more responsibility on the seasonally induced 
increase in downbearing more than the unsubstantiated certainty of 
aggressive tapping.  And, of course, there is the speculation that the 
bridge surface itself rides up the pin in humid conditions, in turn, 
pushing the string further up the pin. The question there would be whether 
the string then follows the board back down in the dry season.

>Unseating on the bridge top tends to occur when the contact point on the 
>bridge top is lower than the indentation in the side of the 
>pin.  Therefore, you are much better off tapping down the bridge pin than 
>the string.

But this assumes either that the pin is not already bottomed in the hole or 
that you can safely drive the pin into the bridge body, like a nail.

>  Tapping down the string will, at best, be a! temporary measure.

I agree.

>  At worst, it can create a further disconnect as the contact point on the 
> bridge top is lowered due to further compression of the bridge top.

Here it is again.  What do you imagine (I don't know the answer) the 
differential between the force needed to seat the string and that required 
to further indent an already compressed piece of rock maple?  I find the 
Compression by Tapping argument suspect.

>  Furthermore, false beats are usually a product of loose bridge pins and 
> a flagpolling of the pin which creates an oscillation.

The false beats created by loose bridge pins is different from the 
distortion caused by faulty termination.

Of course, neither of us has definitive documented proof of our 
positions.  I, at least, do not.  While this discussion might seem too 
abstract to warrant this amount of time and space on this list, it disturbs 
me to think that the information we disseminate might not be as solid as we 
would like to believe.  Of course, the other disturbing thought is that I 
might be totally wrong and that my subscribing privileges haven't yet been 
revoked!

David Skolnik


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