moment of inertia in keys

[Robert Scott]

In thinking about what good it would be to know the total moment of
inertia of a key together with all its action parts, here is
what I concluded.  The comparison of down-weight and up-weight tells
us how much binding there is in the action centers.  This type
of thing can go wrong for various reasons:  pins too tight in the felt,
verdigris, high humidity.  Each of these has its own treatment.  But 
what could cause a "bad" moment of inertia?  Well, to be honest, I 
couldn't think of anything except bad initial design.  I suppose that 
a piano might have been given the wrong hammers, or perhaps a hammer for 
the wrong note.  But the inertia is determined mostly by the geometry
and the weights involved.  It is not affected by things that go wrong
gradually in a piano.  So I don't suppose that measuring moment of
inertia will ever turn out to be as important a diagnostic tool as
measuring down-weight and up-weight.  But perhaps in a piano factory,
just to make sure that the assemblers put the right parts in, it might
be useful to have inertia measured.  And in a piano factory, such an
instrument could be used on many more pianos, thus justifying its
probable high cost.  It might also be useful if an artist complains
that a piano is "hard to play".  If the static weights and the
inertia are all measured, one might be able to either confirm the
artist's complaint, or else show that he is full of hooey.

Bob Scott
Ann Arbor, Michigan