Moment of Inertia of grand action parts.

[Robin Hufford]

Hello John,
    Just a short commentary on this drawing - later this week I will post a
better description of the altered MOI formula I suggested the use of the
yesterday.    I do think it is important, at least at the moment.   It was
done in a real hurry as is this post and the one yesterday, unfortunately, is
not very clear.
     Your proposed analysis of the moment arms of the action is, I think,
essentially on the mark.  Very similar approaches are taken by Pfeiffer in
analyzing an upright action which he lays out in his book.   I think these
kinds of analyses are, unfortunately, very poorly known in the US even though
they were done, repeatedly I think,  in Germany, the land of mechanical
analysis,  along with other very extensive studies of bearing pressure and
friction and  wear at contact points,  as far back as the 1860's or 70's, if
not earlier.
     In my opinion, it would be better to consider the whippen output to be
the line from the center of the whippen center to that of the jack center.
This is the point where, for much the greater part,  the load of the hammer
assembly is first reacted, for lack of a better word.   I don't think this
factor can be ignored without real penalty to the analysis.  The shank input
and output you suggest is the same as I conceive of.  However, the interaction
of the jack and the knuckle needs work which I will have to give more thought
to.
     I will come back later with more on this subject, and agree
wholeheartedly with your other post as to why this is important and why a
dynamic study of the action is, at least equally, if not more so, important
than the conventional, static approach, which, rightfully, gets big play here
but can benefit in a complementary way from such a study.   Some may find this
approach to be tediously mechanical but, to me, using conventional mechanical
concepts inspite of the work this may require is the only way to get a real
handle on what actually goes on in an action.   This may,  actually, render
objective, many of the rather subjective comments on this subject which are
regularly encountered here.  I do not exclude my comments from this criticism
by any means, nor do I mean to disparage the comments made in any way.
     Calculating the mass moments of inertia of the parts about the axial
points in an action is, as you say, a first necessary step.  This, however, is
a formidable and highly repetitious task to do accurately, even for the
keyset, much less the entire action train.   Although I am not sure of its
significance, obviously, every key will have a different value.  Along this
line I had a brief discussion with a nephew in town for the holidays who is a
mechanical engineer as it had occurred to me that surely, there are programs
which can be had which will do this upon data supplied to them.  Something
intervened and I did not get an answer at the time but I think such surely
exists.   Are you aware of such a program?  This,  I think,  this would make
the entire task much more tractable.
Regards, Robin Hufford
John Hartman wrote:

> Inertia Heads,
>
> Here is what I came up with for figuring the total MOI of the action.
> Pretty much the same thing Mark D. came up with. If you plug in some
> numbers you will see that the hammer and shank contribute most of the
> MOI as felt at the key.
>
> 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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