[pianotech] Action Ratio Measuring

[Ed Foote]

Greetings,
            I, like Dale, prefer to measure ratio by hammer rise per key 
depression.  If the key moves x amount, and the hammer moves y amount, 
then there is a ratio that I can use.
         I found that my results were more consistent when I added 10 
grams to the SW before measuring .  The additional weight removes some 
of the variability through additional compression of felt and leather.  
I also stick a needle out the side of the hammer to most accurately 
measure how much it really moves.
        The point of a needle, on a scale in mm, gives information 
precise enough to distinguish the difference in action ratio at the 
beginning and end of the keystroke. They are usually different, and 
correlate , I think, to the capstan's relationship to the "magic line", 
and perhaps to the relationship between the whippen radius, (flange pin 
to jack contact) and the line between whippen center and hammer center, 
(the "other" magic line").


Regards,
Ed Foote RPT
http://www.piano-tuners.org/edfoote/well_tempered_piano.html