Key Leads and Inertia - radius

[Isaac OLEG]

Just by looking at it I guess that if we have a radius that really
move the fulcrum, the hole in the bottom of the key wear faster. I
seem to notice that wear on some Steinway I've seen.

I guess that the effect of the half round dowel is felt in the
acceleration, not in the weight, even if it is a very little.

Being very different on sharps than on white keys...

Best


Isaac OLEG

Entretien et réparation de pianos.

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> -----Message d'origine-----
> De : pianotech-bounces@ptg.org
> [mailto:pianotech-bounces@ptg.org]De la
> part de Sarah Fox
> Envoyé : vendredi 2 mai 2003 04:38
> À : Pianotech
> Objet : Re: Key Leads and Inertia
>
>
> Hi John,
>
> > Thanks for your interesting post. I am saving it for future study.
> > There's likely to be relevant stuff here, especially
> about how some
> > compliance could help efficiency. The impedance matching across a
> > flexing beam (harmonic motion is a factor hear?) is
> intriguing but this
> > will take more time to sift down to a conscious layers.
>
> No, not harmonic motion.  Impedance matching applies in
> many physical
> situations.  It's basically a way to balance force/distance
> tradeoffs or
> voltage/current tradeoffs or so forth.  In rather simplistic terms,
> impedance is a reflection of the amount of force needed to
> effect some sort
> of change.  In mechanical situations, impedance matching is
> generally
> achieved through some sort of mechanism that applies a
> mechanical advantage.
> For instance, in the middle ear, a large sound collection
> area (the eardrum)
> is used to collect airborn sound from the low impedance
> side and transfer it
> (with some degree of leveraging) drive vibrations over a
> much smaller area
> on the high impedance fluid side (the inner ear).
>
> > Were you some sort of circus engineer before heading into
> piano (so
> > called) technology? It looks like the clowns have better
> R&D than us
> > piano people. But I always thought this and now I know for sure.
>
> LOL!  I think Steinway and Sons probably patented a number
> of P.T. Barnum's
> innovations.
>
> > It's not really the rail that is radiused it's a 1/2
> dowel covered in
> > felt replacing the usual ring-o-felt balance rail
> punching. The radius
> > is about 6mm.
>
> Gads.  Well, that answers my question:  It was nothing more
> than a marketing
> gimmic.  (Big surprise.)  The change in mechanical
> advantage from the key
> rolling over a 6 mm radius would be miniscule -- really,
> really miniscule.
> Yes, it's enough to *technically* claim accelerated action
> and get a patent.
> But why bother?
>
> What I had envisioned was a very broad radius (dunno...
> perhaps 25 cm or
> more) that would shift the fulcrum point more
> substantially.  Of course this
> would cause the keys to slide vertically on the balance rail pins
> (slightly).  I don't know if that would present a problem.
>
> BTW, I had another thought after I fired off my last post.
> The springboard
> mechanism used by acrobats also achieves something else.
> Suppose a heavy
> acrobat is to propel a light acrobat into the air (much
> higher than the
> heavy acrobat's original drop point).  There becomes an
> issue of where to
> place the fulcrum, if a standard fulcrum is used.  If it is
> placed in the
> center of the board, for instance, not all of the kinetic
> energy will be
> transferred, and the heavy acrobat will hit the ground with
> a bump (wasted
> energy).  The fulcrum point would need to be off-center in
> proportion to the
> weight differential.  At that point, there would be an
> impedance match.
> However, with the radiused fulcrum, placement is not
> particularly relevant.
> At some point in the roll, impedance will be matched.  Full
> transfer of
> kinetic energy will occur.  Carrying this lesson back to
> the piano, how does
> one design a piano's action to work equally well for the
> light fingers/arms
> of a 6 yr old student and for the heavy fingers/arms of a
> large-framed man?
> With a radiused fulcrum.  Interesting application.
>
> > What's a "Wissner"?
>
> My piano -- an obscure make from the early 20th century --
> a very nice
> instrument in need of lots of TLC.
>
> Peace,
> Sarah
>
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