At 10:12 AM -0400 10/21/00, Farrell wrote:
>Hi Bill. Concerning the posts below. I think the two viewpoints concern
>different objectives. The Stanwood/weight
>evaluation/optimization/customization of an action takes and EXISTING
>physical action, characterizes it, and provides a base for modification if
>desired. I think what Ron Overs is referring to when he speaks of starting
>with lengths and arcs is the fact that he designed his action with lengths
>and arcs (can't do drafting with a weight set and a scale!), and came up
>with a great design.
Agreed!
>THEORETICALLY, the length and arc thing should work just as good as the
>weight-based approach IF everything is properly mathematically
>characterized. Likely, with so little friction loss, the Overs action lends
>itself well to length/arc characterization, yielding accurate results. Take
>you or me with our calipers and rulers, measuring, ESTIMATING capstan/wippen
>heel contact points (ya ever look close there - its impossible to tell where
>the contact actually is - and it moves through the arcing process! - same
>with the knuckle/rep lever/jack contact), etc. Then using the length/arc
>analyses and what do we get? Something close - if we measured accurately.
The mathematical model for a grand piano action is so complex that
when Stephen Birkett went to construct it, he needed grant funding!
Yes, I have looked at the cap/heel contact. I'd guess that both the
friction would be described by an integral (the sum of all contact
between that curve of a hard cap crown and the curve of the soft heel
felt which wraps around that cap crown). Possibly, the leverage could
be summarized by the highest point on the cap. Both of these will
undergo change as the cap and the heel move through the keystroke
cycle.
And speaking of "ya ever look close there", did you ever watch a jack
get momentarily pulled backwards (squashing the jack button felt)
which the cycle first starts up?
>You are right, the weight/scale method bypasses all (with good technique and
>accurate equipment) measurement problems, and accurately incorporates the
>hard to determine contact points and friction losses. Its the way to go for
>sure when you have an action sitting in front of you. It sure is the way
>I'll be doing it. However, if I had some great vision of a new kind of
>action - I would sit down at the drafting table and brush up on my lengths,
>arcs, tangents, vector analyses, etc.
This dream action of yours (and Ron's patented design) would lend
itself to out-in-the-field application, depending on whatever string
heights the given piano left the belly room with, and how carefully
the action department plopped the top action down on the keyframe.
>It would though, be interesting to take an existing Overs action and do a
>Stanwood analyses on it. Could we/ would we find any surprises?
I would not be surprised to find a very well hung action! I would
also not be surprised if we could back in time to the NY Steinway
factory in the years 1945-1990 and have them install Overs actions in
all their grands to find plenty of work for David Stanwood to do.
One correction to my earlier post on acronyms:
SBR: Strike Balance Ratio, or the ratio of a note's Strike Weight as
inferred at the front of the key, by a series of tares, to the actual
strike weight. This is the expression of the action's overall
leverage as measure by weight.
Bill Ballard RPT
NH Chapter PTG
"May you work on interesting pianos."
...........Ancient Chinese Proverb
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