[pianotech] Action Ratio measuring

[David Stanwood]

>Date: Fri, 21 Sep 2012 07:56:11 -0700
>From: "David Love" <davidlovepianos at comcast.net>

>BTW just one added comment.  Calculating the action ratio by weight, as in
>the Stanwood SWR method, I have found to be totally unreliable as there are
>simply too many opportunities for measurement error.

>David Love

Dear David Love et al,

I've been trying to understand your statement: "Calculating the 
action ratio by weight".   Do you mean calculating the distance ratio 
by the weight method?  If so I think it is important to distinguish 
between distance and weight ratios.  One is influenced by gravity 
vectors and the other not.  So they are not necessarily the same.  I 
stand by my opinion published in the PTG Journal that the best action 
setups exhibit a distance ratio that is equal to or higher than the 
weight ratio, the higher the better.  This relationship is effected 
by the set up of the arc geometry, an important and deep subject 
indeed.

I defend the calculation of SWR or Strike Weight Ratio as a viable 
and reasonably repeatable method.  Those of us who practice Component 
Touch Weight balancing know that the determination of the SWR or 
Strike Weight Ratio level is an essential ingredient for calculating 
Front Weight Specifications.  The technique has been practiced and 
continues to be a highly valued tool by many in our profession. 
Those of us who utilize this method know that calculating Strike 
Weight Ratio on a single note and drawing a conclusion about the 
action as a whole is, in your words: "totally unreliable".  However, 
as soon as a greater number of measures are taken and averages looked 
at, the information becomes more and more reliable and totally useful.

I suggest the same statistical approach when drawing conclusions 
about the calculation or measurement of distance ratios.  Best to 
measure sample notes across the keyboard and look at the average 
level of the action as a whole.  There are plenty of opportunities 
for error in measuring between distance points as we see by the 
discussion and questions.   Also there are naturally variations in 
action ratio due simply to unevenness in the construction of action 
components.  Balance Rail pin lines are not straight, capstan lines 
vary a lot, and when you look closely at knuckle placement you will 
find there is plenty of opportunity for variation.   Add this to 
measuring errors and we have a good formula for cumulative error or 
variation which result in action ratios that uneven by varying 
degrees from note to note.  Statistical method is the only way to 
avoid or minimize false perception and this means taking enough 
samples to draw real conclusions.

In my work and consulting we use three levels of sampling:

Minimal = middle c2,c#2c4,c#4,c6,c#6 or notes 16,17,40,41,64,65  for 
quick evaluation
Partial = all the c, c#s    for determination of levels
Full    = all 88 notes      For StrikeWt calibration and 
documentation of the action "as was"

Hope this helps.

David Stanwood