Key Leads and Inertia

[Mark Davidson]

I wouldn't say that static balancing is meaningless, but for Stanwood's
system
to work, you have to have smooth weights AND smooth geometry.  I think
the latter is understood, but not necessarily emphasized enough.  Without
smooth geometry, the system falls apart pretty quickly.

For instance, add two equal weights to a key, one in front of the balance
rail and one behind, such that the FW is not changed.  Correct me if
I'm wrong (like you wouldn't) but I don't think any of Stanwood's
measurements
can detect the presence of those weights.  But adding those weights
violates the "smooth geometry" assumption. That is why Stanwood
recommends adding the key leads as near a single position in all keys as
as possible.

I don't think Stanwood's system is invalid, but there are still some things
that bother me about it.

First, the keys are the heaviest moving part of the action, but
unfortunately
have the most irregular geometry (I'm talking about the rest of the key, not
the leads).  Each key is a different shape, black keys different from
white keys, different widths, etc.  So the "smooth geometry" assumption
holds up least well in the keys, which have the most weight.  This is
unfortunate.

Second, the thing we ultimately want to measure is really key acceleration.
Yet there is NO direct measurement of acceleration.  The test is to give it
to a pianist and see if he/she likes it.  Stanwood's solution here is
basically
"lots of experience", combined with smooth weights and smooth geometry
(I know that is a bit oversimplified, but I'm trying to make a point here).

So here is a suggestion for improvement.

1. measure the "pianissimo weight" -- the amount of weight that when placed
on the key
    will cause the hammer to actually hit the string -- to the nearest gram,
and plot the curve.
    (this might be an interesting before/after measurement for someone's
next
    balancing job)

2. add "balanced weight" to the keys as described above, adjusting the
    amount of weight and/or distance from balance rail in order to
    smooth out the pianissimo weight.

This suggestion has the immediate problem that you are once again adding
weight
some of which is used to overcome friction.  Smooth or very low friction
would be required
for this to work well, and some experimenting to determine how much of the
additional weight
goes toward friction unevenness vs. inertial unevenness.

Suggestion 2 is to find a way to directly measure the rotational inertia
of the keys.  That's hard, but not impossible.  Then add weights
to smooth out both balance weight and key inertia.

-Mark


----- Original Message -----
From: "David C. Stanwood" <stanwood@tiac.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Tuesday, June 10, 2003 7:41 AM
Subject: Re: Key Leads and Inertia


> At 10:17 AM 6/10/03 +0200, you wrote:
> >When somebody can put forward physics/mathematical proofs or reasonings
> >that show conclusively (or even close to conclusively) that static
> >balancing is a meaningless componet for any wholistic concept of dynamic
> >balance, then perhaps we on this side of the fence will take notice.
>
> Thanks for your comments Richard.... However no proofs or reasoning will
> override the simple truth of whether or not pianists like it...
>
> Right?
>
> David S.
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives