What matters most ?

[Richard Brekne]

Bill Ballard wrote:

> At 2:08 PM +0200 8/23/03, Richard Brekne wrote:
> >Whats is more important to the <<heaviness>> of the action, the inertia
> >of the hammer and top action, or that of the key.
>
> I'd vote for inertia in the top action. From a design standpoint, and
> a mechanical one. First, someone setting up the action has far less
> control over it than key inertia. To elaborate, what determines top
> action inertia is SW and the ratio of hammer shanks and wippens. Once
> those parts have been selected, there is a limited extent to which
> top action inertia can be adjusted. (As for as SW, maybe if your
> lucky, .75g downwards. KR, which I'd call bearing directly on top
> action inertia and not on key inertia, provides more of a means of
> adjustment but at great extra effort.)

Adjusting Key ratio means also adjusting the whippens ratio agreed ? And if in
combination with a change in knuckle diameter or placement of the knuckle this can
change the top action leverage quite a bit correct ? And since top action inertia
is by far dominated by the mass of the hammer moving at whatever velocity its
moving at... isnt the choice of hammer strike weights quite a determinant factor
relative to top action inertia ?


> The only reason to adjust key
> inertia would be in meeting the requirements of top action inertia.
> So from a design standpoint, I'd say that top action inertia is the
> one to pay attention to. Key inertia is the tail on the dog which
> wags when its's happy with the weight of the rest of the dog.

I think I like this analogy... grin... have to think on it a bit....

>
> Mechanically, I'd also vote top action inertia. The top action is the
> driven portion of the system and the key is the driver. If the driven
> portion is lighter than the driver, there is the good chance in some
> circumstances that he top action will "fly away" from the key. (Have
> you ever had a pianist talk about "fly-away" hammers?) On the way up
> the top action inertia needs to be greater than the key. Otherwise
> coupling (and as a result, control) will be weakened. In effect, the
> driven needs to act like a brake on the driver.

This is a good point. I was origionally more after what plays the most important
part in the sensation of "heaviness", and at what point one becomes so dominant as
to make changes in the other meaningless.... or nearly so. But as Mike started out
with... I was bound to get lots of angles on this.. What kind of <<usual>>
configuration do you run into that meets the fly away condition above then ?

>
>
> >Or if there exists a
> >kind of border condition where one becomes more important then the other
> >and vice versa.... what is that condition ?
>
> You mean like Steven Birkett's soft and hard zones? There would be
> two ways to determine this. 1.) happen to be Steven Birkett, with all
> his years of physics, math and the analysis of mechanical systems. of
> 2.) do a massive survey of pianists under the controlled experimental
> circumstances proposed by David Anderson. Mind you, the existence of
> such a cross-over zone/point is only speculation at this point, and
> the variables which would cause that cross-over are as yet unproposed.

No.. I wasnt really thinking along the lines of Stephens zones... they are for key
inertia only to begin with. Tho when you first mention this.... it perhaps is worth
thinking through in perspective of some of the other points being brought up...
particularilly David Loves hinting at how individual ratios sum together
differently to create the same overall action ratio. That was one of the main
reasons I saw in taking Stanwoods Balance equation and re-writting it back in the
more general product form it was derived from... so one could see the roll each of
the individual levers was playing a bit more clearly.

>
>
> Bill Ballard RPT
> NH Chapter, P.T.G.
>

--
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