Key Leads

[Michael Wathen 556-9565]

>>>>
Once again I will raise the dreaded moment of inertia to answer this
one. There is a difference. The static (touchweight) is based on the
first moment of the key about the pivot and varies as the distance
between lead mass and pivot. The dynamic (feel) of the key is based
on the second moment (moment of inertia) and varies as the square of
the distance between lead mass and pivot. Thus when you move the
leads to the middle of the key and *slightly* increase to balance the
touchweight you reduce the moment of inertia significantly
(even though the leads are a bit heavier)...hence the key feels
different.

Another analogy...golfclubs are (or used to be) sold in sets which
were statically matched (i.e. the first moments about the grip were
the same)...called `swing weight', which is identical to D.Stanwood's
strike weight! Recently some manufacturers started making sets that
are dynamically mateched (i.e. the second moments are the same). You
can't match both first and second moments, because one varies in
proportion to distance whereas the second varies as the square of the
distance.

Stephen Birkett (Fortepianos)>>>

Excellent analogy!

I have removed leads and rewieghted.  After the leads are removed I use
a Forstner bit to make the hole clean (they are usually tapered). Next
I make appropriate size plugs to go in these holes.  Now I can rewieght
without fear of my new holes that I will drill running into the old holes.

Michael Wathen
University of Bob