Fw: Touch Weight

[Don A. Gilmore]

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  ----- Original Message -----=20
  From: Isaac sur Noos=20
  To: Don A. Gilmore=20
  Sent: Monday, December 22, 2003 4:34 PM
  Subject: RE: Touch Weight


    Don, hello, I guess I get it.=20

    May I understand correctly that the angular position does not change =
the static balancing or is it only m.o.i that is unaffected ? (say that =
because wehn we change the attack angle of a key we change leverage, I =
also wandered if there is some effect in regard of the mass itself)

    Well, I think I'm following you.  We have the term "static =
balancing" in engineering, but I'm not sure if it has the same meaning =
as in your profession.  We consider static balancing that which balances =
a pivoted object when at rest.  Let's consider a fan blade.  If a fan =
blade is out of balance, one blade will tend to sag to the bottom due to =
gravity.  When it is properly statically balanced, you can rotate it to =
any position and it will stay; the center of gravity is exactly at the =
pivot point.  Static balancing is all about gravity.  [In contrast there =
is also "dynamic" balancing which takes into effect rotation.  An object =
can actually be in perfect static balance and not be dynamically =
balanced].

    The angle of placement of a weight does affect its balancing =
properties since gravity is always in a plumb direction.  For example, =
if you place a weight three inches to the right of a pivot it can =
counterbalance an equal moment on the other side, like a scale.  But if =
you place it three inches above the pivot it doesn't balance anything =
since gravity acts directly toward the pivot and there is no leverage.  =
However, either of these placements of the weight would result in the =
same moment of inertia, since you have the same raduis and the same =
mass.  Confused yet?

    Let's consider moment of inertia in terms of a "black box" with a =
shaft sticking out of it.  If you turn the shaft and it is hard to start =
turning and then hard to stop (as if there were a flywheel in the box), =
it has a high m.o.i.  If it is easy to turn (as if there were just a =
plain shaft in the box) then it has a lower m.o.i.  What the rotary =
object in the box looks like is immaterial.  It might be a round wheel, =
or it might be a hammer pivoted at the base of its handle.  But any two =
objects with the same moment of inertia will feel exactly the same =
(neglecting gravity) when you twist the shaft, no matter what they look =
like.  Think of m.o.i. like "rotational mass". =20

    Balancing is affected by gravity; inertia is not.  If you took your =
black box to the moon, or out into space with zero gravity, the shaft =
would be exactly as difficult to accelerate and stop when you turn it as =
is was on earth.  The same is true of mass.  A 275 lb. football =
linebacker may only weigh 90 lbs. on the moon, but he will hit you just =
as hard if he tackles you there as he would in Green Bay, since he has =
the same mass.

    Thanks for your analysis and words it helps ! We piano technicians =
have generally a small undertanding of what goes on in the action really =
! On the contrary, some friends that studyed accoustics and physics at a =
somehow interesting level said me that their understanding was not =
really helpful when it comes to tune, regulate and voice a piano !

    Best regards and good late Christmas shopping !

    BTW, Are you the inventor of the "self tuning piano system", or may =
is miss something ? if it is the case, I have a few questions I like to =
understand some points on the process, if you don't care.

    Yes, that's me.  I wrote an article in the Journal about it in July =
2002.  The PTG asked me to join after that.  I would be glad to answer =
any of your questions (or anyone else) about the system.

    Don A. Gilmore
    Mechanical Engineer
    Kansas City

    Greetings.

    Isaac OLEG
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