[pianotech] measuring action ratios

[Dale Erwin]

Hi Joe
 I'm sure the archive are filled with our banter about this but here goes. 
 A 6 to 1 ratio means for every mm of key movement the hammer moves a corresponding amount. SO lets say 6 mm of key movement equals 36 mm of hammer movement. That's the 6 to 1 were talking about. What one actually measures could be whatever the action says. In general the  ratios we find and are in the desirable range are between 5 to 1 and 6 to 1
Many action systems used a 6 to one ratio.ie Steinway for a century at least. What this means is that the system will only tolerate light weight hammers, and the regulation will require a shallow dip(,,370- .375/10 mm at the pin)  and a long blow distance.(1 7/8th /48 mm)If heavy hammers are applied to a system design at 6 to 1 the touch will become heavy. Installing leads to compensate only makes matters worse with increased inertia. Moving the knuckle from 15.75 to 16.5 or 17 will lower the ration. This allows for a bit more hammer weight to be carried with less leading and less inertia. The regulation will need to change as well. Shorter blow & a longer dip/key travel.
In many cases simply moving the knuckle will not yied my desired ration of 5.5. The next move is moving the capstan towards the balance rail to lower the ratio further.
 I'm sure others can elaborate and explain this better and more thoroughly and it can be more complex as David is pointing out. but....
  I think you get the idea.
Dale



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

 
  





-----Original Message-----
From: Joseph Garrett <joegarrett at earthlink.net>
To: pianotech <pianotech at ptg.org>
Sent: Wed, Jan 16, 2013 3:37 pm
Subject: Re: [pianotech] measuring action ratios


Thanks to all with the pics of gauges, etc. Now, to my main question: Once
you have done this bit with the gauge and the math, and you have this ratio
number, .... what do you do with it? Or, to put it another way: what does
the number tell you? Or: Of what worth is this number? Or: what does it all
relate to? Anyone care to give "us" the straight poop?<G>
Regards,
Joe


Joe Garrett, R.P.T.
Captain of the Tool Police
Squares R I


 

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