Touch Weight

[James Ellis]

Don A. Gilmore, mechanical engineer, Kansas City, is exactly right.  I used
the wrong words.  I should have said "property" instead of "quantity", and
I should have said "acceleration" instead of "velocity".  Also, the moment
of inertia is proportional to the square of the radius about the center of
rotation, or the pivot, but that relates back to the change in velocity,
whether it be acceleration or deceleration.  So my first statement was not
so far off after all.  Other than that, I'm saying the same thing Don is,
and I'm also sticking to my guns about the point I'm trying to make.

You can go through the whole tedious process of calculating the moments of
inertia of the entire action, and adding it all up.  You can also treat the
whole thing as a compound lever system, which it is, the shank ratio, the
wippen ratio, the key ratio, etc.  You can't use any nice formula for it,
because it is a compound lever system, and these pieces all have irregular
shapes, sizes, and mass distributions.  You will have to take it piece by
piece by piece.  With the exception of the extreme high treble, when you
are done, you will find that the hammer head out on the end of the shank
dominates the picture with respect to the moment of inertia, and as someone
said, there is not much you can do about that, assuming the hammer has
optimum mass in the first place. 

You can reduce the moment of inertia of the keys by moving the leads closer
to the centers, but you will have to use more lead to get the touch weight
you want, and you will be putting more holes nearer the centers of the
keys, and that will weaken them.  In the low bass, you will have keys with
lots of lead.  When you are all done, you will find that you have not
accomplished very much for the total moment of inertia of the whole action,
because it's the hammer heads out on the ends of the shanks that are
dominating it.  In the extreme high treble, you don't have this problem
anyway.

I used to weigh off keys by concentrating the leads toward the centers in
order to reduce the moment of inertia of the keys, but I came to the
conclusion that it was just not worth it, and I quit doing it that way.

That's the point I was making, and I am sticking with it.

Merry Christmas,

Jim Ellis