[pianotech] Action ratio measuring

[Dale Erwin]

 I had to know, ya know?...so I went to the shop and performed my own first test based on the parameters below in my previous e-mail.  
  The initial action ratio reading using the quick Erwin action ratio block/tester shows a 5.5 action ratio on a Stwy B action from the  last decade. The action is in good shape and regulated.  6 mm of key dip accounted for 33 mm of hammer rise.
  In the next test to insure only 10 mm of dip I removed the punchings and replaced it with hard card board one. So no punching compression at all. Ok Jason?
  I used digital calipers to measure dip as accurately as possible at 10 mm.
 the key was depressed  10 mm and measured;... total hammer rise. Tada !....55 mm  
  So the action ratio is 5.5.
 So this is only one check &  I was more microscopic than usual. So for my money, I'll stick with the quick and simple method of using the action ratio tester first and then  measuring of the leverage. The beauty of crunching the numbers is that the leverage changes become more specific. Usually its the knuckle placement, capstan location or changing both in order to achieve a specific reasonable action ratio. Beyond that its a new key set with a change in leverage.
Try this yourself
Dale


Dale Erwin R.P.T.
Erwin's Piano Restoration Inc.
 Mason & Hamlin/Steinway/U.S. pianos
www.Erwinspiano.com
Phone: 209-577-8397






On Sat, Sep 22, 2012 at 5:47 PM, Dale Erwin <erwinspiano at aol.com> wrote:

 Cy
 Bering a simpleton myself, I agree.
 If a few of us take a few measurements and compare the data. we'll find out if"Does this average out the "arc" effects? For accuracy lets all do it this way. Use a metric ruler to set the dip at the front of the key. remvoe drop screw and let-off button(or crank it out of the way)Then measure the hammer rise as accurately as possible. 

 All actions are subject the accelerating action phenomena to changing ratios thru the complete range of motion as the capstans is moving further from the wip center pin and the increasing leverage efficiency in the wip. 
 FWIW...I've had brainiacs more smarter than me compute things to the small decimal points and say 6 mm is enough of a sample. Is it? Dunno for sure but seems to work. 



Dale Erwin R.P.T.
Erwin's Piano Restoration Inc.



From: Cy Shuster <cy at shusterpiano.com>
To: pianotech <pianotech at ptg.org>
Sent: Sat, Sep 22, 2012 5:24 pm
Subject: Re: [pianotech] Action ration measuring



Simpler is better -- I like it!


Is this significantly different from using your existing tool, Dale, where you just measure the first part of key travel and hammer rise?


Does this average out the "arc" effects?


--Cy--


Cy Shuster, RPT
Albuquerque, NM


www.shusterpiano.com
www.facebook.com/shusterpiano


On Sep 22, 2012, at 5:57 PM, Dale Erwin <erwinspiano at aol.com> wrote:


From: Jim Ialeggio <jim at grandpianosolutions.com>



Ron said:

<It always annoyed me that the cumulative leverage of the presumed 
moment arms matched so poorly with Dale's 6mm in/out direct measurement. 
Something's wrong, and I'll take direct first.

Jim wrote
My take...the position of half stroke should be determined by 1st 
determining the  full arc the hammer would travel, driven by the key at 
its full dip,  with the hammer unimpeded by the letoff button. Full 
hammer  travel in this scenario is of course more than blow(-)letoff, 
but it exceeds blow as well.
  Jim.
I like the way you think
  Take the let-off button off and toss out the drop screw too. Now nothing is in the way to impede hammer rrise. Now set a very accurate 10 mm key dip, (however one does that) , then set a modest weight on the key to depress it fully, then simply measure the total hammers rise. Likely it will be 55 mm to 65mm. Divide by 10 equals a totally accurate direct measurement figure for action ratio.
Dale
Dale Erwin R.P.T.



Erwin's Piano Restoration Inc.





Jim Ialeggio

-- 
Jim Ialeggio	
jim at grandpianosolutions.com
978 425-9026
Shirley Center, MA


 



 









 

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