Inertia

Ed Sutton ed440@mindspring.com
Wed, 31 Dec 2003 07:44:13 -0500


Ron-

We wrote:
>
> > > And since the leads are there to counterbalance the hammer weight (etc.),
> > > did you double the weight of the lead when you halved the length of the
> > moment?
> > >
> >
> >Ron, given my limits in mathematics, rather than defend my calculations, I
> >would
> >prefer that someone like you would do a few of your own, and tell us what
> >you get.
>
> It's not a math problem Ed, it's a conceptual one. Why are leads put in
> keys in the first place if not to counteract hammer (etc) weight for a
> nominally specific static down weight? Moving the weight to a different
> point on the key requires a different amount of weight for the same
> balance, which changes your inertia calculation. You didn't take that into
> account.

I believe I did take it into account in the calculations, then used the wrong term
in writing.  ;-(
I should have written "with the 48 grams of frontweight magically concentrated at
1/2 or 1/4 of the distance from the balance rail to the keyfront."
>
>
> > > >Again I suspect that the difference would be in speed of repetition.
> > >
> > > Probably, all else being equal, and depending on how much key lead is
> > > actually removed. It has to become noticeable in the power stroke too, at
> > > some threshold level.
> > >
> > > Ron N
> > >
> >
> >Ron, could you expand on your last sentence, please?
> >
> >Ed
>
> What's to expand on? At some degree of mass difference a light key will
> feel noticeably different from a heavy key when you push it down to play
> it, even with a wippen assist spring making the down weights identical.
>
> Ron N
>
Yes, that is the performance import of our discussion.

But at what degree of mass difference does it become possible for a performer to
feel the difference, or for the jack to reset faster?

If the mass differences required exceed the differences we can produce by changing
the configuration of key leads, then we are wasting time and money plugging holes
and moving leads.

If not, then we should be looking for the best lead placement for high
performance.

In regulating pianos, we become accustomed to experiencing that the compounded
result of several barely perceptible adjustments can be significant, so we are
predisposed to believe that subtle adjustments of weight placement will produce a
better performing action.

Jim Ellis and Jon Hartman have shown us some calculations that seem to indicate
that these adjustments don't matter very much.  My clumsy mathematics seem to
agree with them, but I don't consider my math skills very advanced or certain.

Therefore, I'm interested in your calculations and opinion on this, since you have
experience, math skills, and an inquiring mind!

In terms of real world keyweights, do you think it's worth trying to move weights
closer to the balance rail to reduce the moment of inertia experienced by the
performer?  Do you think it is worth calculating the location of each weight, or
just do the best we can to keep the weights away from the fronts of the keys?

In practice, I believe those of us who care have a series of rules of thumb,
perhaps not very clearly stated, that we hope will produce the best location for
key leads.  It might be of use to try to create such a series within this
discussion.

Sometime next week I'll be releading an old M & H AA to produce a front weight
continuity.  If we can resolve all questions by then, it will be the first action
with UltraInertial Key Lead Positioning.

Ed Sutton






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