[pianotech] measuring action ratios

[Dale Erwin]

The action ratio gauge I make for the trade has a pre-printed scale on the back for ease of reference. See attachment.
6 mm isn't just for ease of reference.It cover a wide swath of the keystroke and somewhere between 7 & 8 mm of key travel the l.o. button comes into play. 


 David. Another thing to try is remove the drop screw and turn the L.O. button all the way up. Now take a 10 mm sample or a full keydip/travels worth of hammer movement and see if it changes your outcome.


Dale Erwin R.P.T.




   >>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

 
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