What's all this I hear about Inertia ?

[David Love]

Unfortunately it's not the case in this particular formula because of the
relationship between BW and FW.  Change one and the other changes in the
opposite direction in an equal amount.  Increase FW (front weight) by 5 and
BW (balance weight) decreases by 5 so any change in FW or BW will not change
the value of R.  You cannot change them independently without changing the
other in this particular formula.  Makes sense too since adding (or
subtracting) lead to a key certainly doesn't change the action ratio, it
just decreases the touchweight.    

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Nick Gravagne
Sent: Tuesday, October 07, 2008 10:28 AM
To: 'Pianotech List'
Subject: RE: What's all this I hear about Inertia ?

Hello all,

RE: RicB's statements:

Clearly a change in FW changes the value of the entire left side of the
formula, and hence the equivalent R on the right side.

Review Stanwood's formula.   R = (BW + FW - WW) / SW

Nick says:

I have been following this thread with interest. I am casually familiar with
David Stanwood's protocols, but not intimately to where I can rattle the
terms off the top of my head. 

(My own work is primarily based on Pfeiffer's work in tandem with standard
leverage physics and with more of an eye to downweight and hammer weight.
The distance and force ratios should stand on their own regardless of the
actual weight of the components, as instructive as these may be). 

In the interests of accuracy and fairness, though, may I post the following?


As the above mathematical formula stands, RicB is correct in his observation
that the dependent variable R (whatever that is) is a function of FW. In
fact, any change to the values of either BW or FW or WW will change R.
Inversely, any increase to SW will decrease R.

To demonstrate I have arbitrarily chosen values that have nothing to do with
action values. Here we see FW as 25, then 15, then 5. Note that R changes
directly with each change to FW.

1)	R = (10 + 25 - 5) / 20 = 1.5
2)    R = (10 + 15 - 5) / 20 = 1
2)	R = (10 + 5 - 5) / 20 = 0.5

In fact, note the direct ratio of 10 to 0.5 in that a decrease in FW of 10
causes a decrease in R of 0.5 (technically this ratio would be 1 to 0.05).

Increasing SW reduces R:

4)	R = (10 + 15 - 5) / 25 = 0.8

If it is true as David points out, that when "you reduce FW by an amount
then BW will increase by the same amount and vice versa so the calculation
of R remains the same...", then the above formula as it stands does not
directly reflect this. So there must be prior considerations that
demonstrate the proportional and self-balancing relationship of BW to FW. 

If the formula cannot stand out of context without prior explanations, then
my sense of things is that the term (BW + FW) might be independently
calculated, then referenced as a single term such as Wbf. This way the
formula would state R = (Wbf - WW) / SW. Such a formula can never be taken
out of context. I realize how presumptuous this may sound, not only given
the years of dedication that David has devoted to the subject, but given my
admittedly less than complete knowledge of David's work relative to the
sequence of design investigations. Please accept this in the spirit in which
it is presented.

Although for years we have accepted terms such as BW and DW as balance
weight and downweight respectively, to a third-party mathematician or
engineer these seem to be products of B times W or D times W. Mathematical
convention would reference these values as Wb and Wd (the lower case b and d
would appear as subscripts).

So, regarding David's correction to the formula in that WW should really be
WBW, if this is simply a reference correction but not a value correction
then RicB may have been mistaken referentially but not conceptually (at
least regarding the formula which is my focal point here). In the broader
picture of the thread, if Ric and others have correctly represented
Stanwood's concepts and protocols (or not), I cannot speak to that.

Again, so as not to be misunderstood, the foregoing has been posted in the
interests of accuracy and balance, not to open the floodgates of touchweight
investigations and minutia. The List may wish to pursue this, but it has not
my intention to initiate it.

It is not necessary to supply a complete rundown of David Stanwood's
protocols or sources of same (unless one wishes to) as I think I can
re-familiarize myself with these on my own.

Thanks to all participants for their input. It's always interesting!

Respectfully,

Nick Gravagne, RPT
Piano Technicians Guild
Member Society Manufacturing Engineers