What matters most?

[David Love]

I wish I could elaborate more, but I don't really have any data.  I stands
to reason that there will be differences in response to a 10 gram hammer on
the end of shank if the shank is being accelerated 16 mm from the center
pin or 17 mm from the center pin.  The idea of inertia seems simple on the
surface.  A body at rest wants to stay at rest.  Add mass, it wants to stay
at rest more.  While we use the strike weight as measured from the center
pin flange which works in the static system we are using, what about the
difference in strike weight as measured from the knuckle where the force is
actually being applied.  Wouldn't that contribute to varying degrees of
inertia?  While the combination of different hammer shank ratios and key
ratios may make no difference in a static analysis, I would need to see the
dynamic analysis to believe that it makes no difference through
acceleration.  And while Ed's point that the differences will depend on how
much you are accelerating the system, my hypothesis would be that at a
certain level of acceleration the various levers will handle inertia in
different ways.  In addition, it seems that you would have to take into
account the deflection of the different levers with different setups.  How
does shank deflection fit into all this when you start moving the knuckle
toward the center pin while keeping the hammer weight the same.  Can the
pianists sense that little bit extra lag due to increased deflection
through the first part of the stroke?  It seems to me that there are a lot
of unanswered questions.  For myself, I've found a system that works quite
well: combinations of hammer weight, knuckle position and overall ratio.  I
haven't begun to read Birkett's available research and I'm looking forward
to it when I have the chance and when it becomes available.  For right now,
I've got my nose buried in soundboard stuff.  

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Richard Brekne <Richard.Brekne@grieg.uib.no>
> To: <davidlovepianos@earthlink.net>; Pianotech <pianotech@ptg.org>
> Date: 8/23/2003 9:13:54 PM
> Subject: Re: What matters most?
>
>
>
> David Love wrote:
>
> > The question may seem absurd to the pianist who doesn't even know the
names
> > of the parts, but it's certainly not absurd if the piano isn't
performing
> > well.  As technicians, we need to be able to quantify cause and effect
as
> > much as possible if we are to have any chance of producing a predictable
> > action, soundboard, or anything else for that matter.
>
> I aggree, as I think we all do from this perspective.
>
> >
> > With respect to this question, I think what we are likely to find, and
have
> > found (thanks in large part to David Stanwood), is that a certain
weight at
> > the hammer end works best with certain action ratios.  Moreover, with
> > respect to inertia, how that ratio is achieved will make a difference. 
We
> > can, for example, achieve a 5.6 action ratio with a combination of 16 mm
> > knuckle mounting and .48 key ratio, say, or 17 mm knuckle mounting and
.52
> > key ratio.
>
> Now this is interesting. And I again agree entirely. Yet it seems Stanwood
> himself does not. He believes the particular combination whatever whippen
and
> hammershank ratios that make up the top actions overall ratio is of
little, or
> no consequence... or so he states in his latest writtings. According to
this it
> is the overall SWRatio that is of importance and not the individual
factors that
> comprise that product.
>
>
> > Which one should we choose, given that we have a choice.  The
> > answer, it seems, would lie in how heavy a hammer we wish to use.  A
heavy
> > hammer, from my experience benefits from a long knuckle mounting and a
> > light hammer from a shorter mounting.  Though I can't quantify the
inertial
> > relationships (at this time), it would seem that inertia (as well as
> > friction) would play a role.  The Overs piano that I saw in Reno, for
> > example, had quite a heavy hammer on it.  Thirteen grams or so in the
bass,
> > if I recall correctly.  But it also had a knuckle mounting of 20 mm. 
The
> > overall ratio (I believe, Ron can correct me on this) was about 5.7.
>
> I believe Ron Overs had David measure his action according to his
vertical force
> priority measurements. I dont remember what Ron mentioned was the result
of
> that, and the result of his own method, but perhaps he might share that
with us.
>
>
>
> > That
> > piano certainly did not suffer from any inertia problems (it also had
> > assist springs BTW).  That may not have been the case had the overall
ratio
> > been achieved with a shorter knuckle mounting and a lower key ratio. 
Heavy
> > hammers, contrary to other thoughts expressed, will not necessarily
create
> > inertia problems given the overall ratio and, moreover, the ratios of
the
> > component levers are a good match.
>
> I wonder if you might expand a bit on how you see the hammers inertia
being
> changed by a change in knuckle diameter while compensating elsewhere to
keep the
> top action ratio and/or the overall ratio the same.
>
> >
> > At least that's my take on it.  So in answer to the original question:
> > None of the above.  High inertia in the top action can feel just as bad
as
> > high inertia at the key.  I'll wait for Birkett's research to try and
> > quantify that relationship further.  Fortunately, we don't usually have
to
> > make that choice.    In general, I'd say that the hammer weight and
knuckle
> > mounting position should move in the same direction.  Once that number
can
> > be quantified, then all that's left is to establish the key ratio that
> > gives the desired overall ratio. That ratio (assuming no assist springs
or
> > magnets) will have to consider both the resultant front weight of the
key,
> > or key inertia, and regulation requirements.
> >
> > David Love
> > davidlovepianos@earthlink.net
> >
>
> Thanks David. One of the angles on this I'd like some feedback on goes to
the
> question of just how important the keys inertia really is... and when
does it
> become important. At what (if any) point hammer inertia becomes so
dominant that
> any reduction in key inertia is not of any real benifit ? Overall
leverage can
> come into play, as well as the weights of the parts being leveraged. The
lower
> the overall ratio (regardless how its taken) the less hammer velocity for
unit
> key velocity.. That directly alters the inertia balance.... the lower the
> ratio.. the more important key intertia becomes... and vice versa. This
is one
> of the reasons why I see Stanwoods claim that the overall ratio taken as
a whole
> is the only thing that is important.... it disregards that for same ratios
> differeing inertia relationships can exist for the hammer and keystick.
>
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> UiB, Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
> http://www.hf.uib.no/grieg/personer/cv_RB.html
>