Center pin friction (was Re: Schaff spring)

[Terry]

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Center pin friction (was Re: Schaff spring)torque1    ( P )  =
Pronunciation Key  (t=F4rk)
n.=20
  1.. The moment of a force; the measure of a force's tendency to =
produce torsion and rotation about an axis, equal to the vector product =
of the radius vector from the axis of rotation to the point of =
application of the force and the force vector.=20
  2.. A turning or twisting force.
Terry Farrell
  ----- Original Message -----=20
  From: Phillip Ford=20
  To: Pianotech=20
  Sent: Saturday, December 18, 2004 11:15 AM
  Subject: Center pin friction (was Re: Schaff spring)


    Now I haven't tried this, so I may well be speaking out of =
ignorance, but I have a reasonable concept of how much flange friction =
there will be with 3-4 grams of resistance. A jack weighs almost =
nothing. Seems to me if the jack needs to swing freely 7 full swing =
cycles, that would require almost no friction in the center. Three to =
five grams friction in an action center with a shank and hammer hanging =
from it will swing maybe three full cycles - and that has tons more =
momentum. Seems like something may not be right here???

    Terry Farrell


  I think there a couple of things askew here.  One is that some people =
are talking about hammer flange center pins and others are talking about =
jack center pins.  Two is that, with regard to center pin friction, a =
gram reading by itself is meaningless.  Action centers rotate, and that =
rotation is caused by a torque, not a force.  And the friction =
associated with them is measured by a torque, not a force.  A gram =
reading is a measure of force.  To get a torque you have to know the =
distance from the center that the force is applied.  On a hammer flange, =
4 grams applied next to the screw hole gives a completely different =
torque than 4 grams applied at the tip of the flange.  If you're going =
to specify a gram reading for flange friction then you also need to =
define the point at which you're taking that gram reading.


  Phil Ford
  San Francisco, CA, USA, Earth
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