[pianotech] action ratio

[Joseph Garrett]

Nick,
Yes, I do get it. Was just not up on the current "buzz words"!<G> I don't agree with some of the major ASSUMPTIONS in your explanation, but I'll go along anyway.<G> Hope all's well in your world, Much thanks for the enlightenment.<G>
Best,
Joe


----- Original Message ----- 
From: Nicholas Gravagne 
To: joegarrett at earthlink.net;pianotech at ptg.org
Sent: 8/25/2012 10:48:56 AM 
Subject: Re: [pianotech] action ratio


Joe,

You actually DO know this. "Key in", etc. is that portion of an action component  that represents the effort or activation arm of the lever in question. The "outs" are the resistance arms. So in broad terms, "key in" is the front half of the key and the key out is the back "half" from balance to capstan. Ditto on the whip and shanks. Multiplying the ratios of the key, whip and shank (each component having its own effort and resistance arms), as they exist on the left hand side of the equation yields the action ratio (AR), also referred to as the transmission ratio by Pfieffer in his books. 

I don't know if it shows up in all email clients, but the entire equation as posted, both left and right hand sides should be shown as as division, which is to say these also represent ratios. Given that, then the left side ratio (even though it derives as a product of three ratios) is equivalent to the right side ratio (even though the right side indicates --- or should depending on how you see in in the post --- as blow-distance-minus-let-off (divided by) key-dip-minus-aftertouch). 

Since there are so many variables here, there can be no one standard for aftertouch. So without running a bunch of example numbers right now, let's say we multiply the three component ratios and the AR works out as 5.8 to 1. Another action might yield 5.58 and so on. However, blow distances and let-offs do not generally vary much, so these can almost be stated as fixed constants (say 46mm blow and 2mm let off). Key dips can vary more so, but again, about 10mm plus or minus. 

Thus, given the equation it is clear that the left side must equal the right side, say 5.8 on the left side must somehow equal 5.8 on the right. If blow distance is locked in at 46 and let off at 2, then this equals (46 - 2) or 44 . Now if key dip is locked in at 10, then all that is left unknown is after touch. Some simple algebra yields the unknown after touch as 2.41mm (0.095"). The formula will now balance since:

(Let side Action ratio) of 5.8 is to1 as the: 
(Right side Regulation Parameters) of (46 - 2) to (10 - 2.41) or 44 to 7.58. Thus the right hand and left hand ratios are satisfied at 5.8

Now having said this, note two things at least:

1) given the action ratio (AR) as fixed, which it is, once established one way or another, the only "fudge-ables" are action regulation parameters. But regardless of what you do with the regulations, these will always balance the AR value.

2) the reason there can be no one aftertouch value to fit all situations is that the ARs from one action to another are not all the same; and so "as goes the AR, so goes the regulation" (which includes the aftertouch portion).

And so, Joe, you old curmudgeon and Captain of the Tool Police, I really DO think you get this <G>

NG 


Key out x wippen out x shank out = blow distance - let off
 
Key in wippen in shank in key dip - after touch



On Sat, Aug 25, 2012 at 8:34 AM, Joseph Garrett <joegarrett at earthlink.net> wrote:

And they mean what?! I'll need something a bit stronger, like a good single malt!"Key in"??? What does that refer to? Just because some brainiac thunk that up, doesn' mean squat unless an explanation is with it imo.<G>
Joe


----- Original Message ----- 
From: Dale Erwin 
To: joegarrett at earthlink.net;pianotech at ptg.org
Sent: 8/25/2012 8:18:25 AM 
Subject: Re: [pianotech] action ratio


These are formulas used by Nick Gravagne , David Stanwood and others to determine the overall action ratio. Which is a very useful thing to know. 
 Need some Excedrin now Joe?


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: Sat, Aug 25, 2012 8:03 am
Subject: Re: [pianotech] action ratio


David said: "One formula for the action ratio has been given as:
 
 
Key out x wippen out x shank out = blow distance - let off
 
Key in wippen in shank in key dip - after touch
 
 
 
Does anyone happen to know what the standard (or minimum) aftertouch is in
this formula or how it was derived? "

David,
First of all, I need to know what the hell "key out...." and "key in..."
means. Have never heard the terms. I suspect if I knew, I'd get a headache
Joe


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





-- 
Nick Gravagne, RPT
AST Mechanical Engineering
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