Action Analyses (was Capstan Relocation)

[Farrell]

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.

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.

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.

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?

Terry Farrell
Piano Tuning & Service
Tampa, Florida
mfarrel2@tampabay.rr.com

----- Original Message -----
From: "Bill Ballard" <yardbird@sover.net>
To: <pianotech@ptg.org>
Sent: Saturday, October 21, 2000 8:17 AM
Subject: Re: Capstan Relocation


> At 7:42 AM +1000 10/21/00, Overs Pianos wrote:
> >At 10:30 PM -0400 19/10/00, Bill Ballard wrote:
>snip>
> >>Very nice graphic. You're still defining the problem in the linear.
> >>What we're selling to the pianist is not linear but but in the
> >>dimension of mass and weight (more specifically, inertial and
> >>gravitational forces). At what point do you move from adjusting
> >>length to adjusting weight?
> >
> >I presume you are referring to the relationship between leverage
> >ratios and arc relationships (and the way in which we might approach
> >design solutions for an action in a dynamic sense, as apposed to the
> >static measurements we might make). While these are separate matters
> >which both influence dynamic performance, when designing and action,
> >I would consider the arc relationship as a first consideration,
> >since the overall layout of the action will determine the arc
> >relationships. Nonetheless, leverage ratios must also be factored in
> >to allow the final design to function efficiently with the desired
> >key dip and hammer blow distance.
>
> My point has already been made, and we diverge, respectfully. The
> motion of arcs is the rotational version of distance. You're working
> the problem in the linear dimension. David's New Metrology works it
> in the weight dimension. Certainly you can resize lever arms and
> relocate pivots to arrive at a desired overall leverage ratio,
> coinciding with the proper relationship of axes and contact points.
> But still missing from this view is a direct view of what happens you
> load the weight of a hammer on the payload end of this lever train.
> Certainly,
> Hammer/key ratio = (B/A)*(D/C)*(E/F)
> will tell you how much the action leverage will increase the hammer
> weight as encountered at the front of the key. But without a weight
> measure of the existing balance of the key (FW, or how much heavier
> the front of the key than the back), there is no indication of
> whether the above mentioned hammer is too heavy for the given action
> (however neatly its arms and axes have been revised).
>
> The notion that leverage can be expressed just as well by weight
> measurements as linear may be a new one, but it is very attractive to
> me.
>
>snip