[pianotech] measuring action ratios

[Ed Foote]

   >>A simple block of wood with an extension (mine is a machine screw) 
that laysacross the keys and that depresses a key exactly 6 mm whereby 
you then measure the amount of hammer travel and divide that by six to 
give theaction ratio.<> Not sure why it's 6 mm, tho. Why not 5 mm, 
which is 1/2 of most key dips <<

Greetings,
    I like the 6 mm for its ease of reference. I use a jig like Davids, 
and I place a needle through some unused part of the hammer felt so 
that I can measure its rise against a scale as closely as my nearest 
pair of reading glasses lets me.
       It it goes up 36, its a 6:1, 30mm and its a 5:1, all points in 
between are fairly easy to approximate, i.e. 33 mm would be a 5.5:1,
     If anybody takes the time to be really careful, the ratio can be 
seen to change between the first 4 mm of key travel, and the last 4 mm. 
At least, I have.  I think it gives a good indication of how to 
optimally arrange the congruence of the capstan's arc with the 
whippen's.
regards,



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