Moment of Inertia - numbers in the air !

[Isaac sur Noos]

Hello, Slight correction about that famous video of a piano action at
work.

At forceful play, the key bottom (on that movie) before the hammer
have even moved - I let you imagine the bending.

1/400 sec is a range of time where the hammer travels its 45 mm , or
the key move 10 mm.
That means in that short fraction of time we have an acceleration from
0 to 65 km/h

No doubt force at work are certainly enough to generate a lot of
bending.
More details as soon as I'll have them


Best Regards


------------------------------------
Isaac OLEG
accordeur - reparateur - concert
oleg-i@noos.fr
19 rue Jules Ferry
94400 VITRY sur SEINE
tel: 033 01 47 18 06 98
fax: 33 01 47 18 06 90
mobile: 033 06 60 42 58 77
------------------------------------


> -----Message d'origine-----
> De : pianotech-bounces@ptg.org
> [mailto:pianotech-bounces@ptg.org]De la
> part de John Hartman
> Envoye : dimanche 28 decembre 2003 15:21
> A : Mark Davidson; Pianotech
> Objet : Re: Moment of Inertia of grand action parts.
>
>
> Mark Davidson wrote:
>
>
> > I made an attempt to relate hammer, wippen and key
> inertia to total
> > reflected inertia here:
> >
> > https://www.moypiano.com/ptg/pianotech.php/2003-August/140901.html
> >
>
>
> Mark,
>
> Thanks for sharing this with me. Just yesterday I came to
> exactly the
> same conclusion. I am doing a drawing to show the
> acceleration ratios of
> the wip and shank in relation to the key. The fact that we
> both came up
> with the same formula is encouraging but to be sure we need
> to have Don
> go over it.
>
> Have you plugged in the MOIs? It looks like the shank and hammer
> contribute about 12 times or more of the total I as felt at
> the key. If
> the formula is right it shows how unimportant changes to
> the key MOI is
> in relation to overall efficiency. Also, if there is any benefit to
> pattern leading it is not to make the action feel even from note to
> note. Adding lead to the key is not the big evil commonly
> thought unless
> it has some effect on repetition.
>
> I think we are going to find that the biggest problem with
> increasing
> the mass of the action parts is the losses due to bending
> and compliance.
>
> I still need to complete the kinetic model of the action
> but I can see
> ahead to the next step. Maybe you are already there. Is
> there a way to
> convert the kinetic forces developed at different levels of
> play into
> static loads. Then we can see how these loads bend the
> shank and key. It
> would be great if this could lead to a formula for finding
> the terminal
> velocity of the hammer.
>
> John Hartman RPT
>
> John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
> Rebuilding Steinway and Mason & Hamlin
> Grand Pianos Since 1979
>
> Piano Technicians Journal
> Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]
>
>
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