[pianotech] Action Ratio measuring

[Dale Probst]

Dale Probst
Registered Piano Technician
Ward & Probst, Inc.
dale at wardprobst.com
940.691.3682



On Sep 21, 2012, at 6:10 PM, Dale Erwin wrote:

> Hi David
>   The first step here is to always check the displacement first and then see how the numbers add up after measuring. I get numbers typical to the ones you state. I think Rick Wheeler at Roseland key uses Dels Method and I could never reconcile Ricks A.R. numbers with mine....till now. 
> and logically displacement is displacement...it doesn't lie. Its not a microscope but its a quick magnifying glass. Usually the difference between displacment numbers and measured number is no more than 1/10. ie 5.93 to 5.83
> 
> Dale Erwin R.P.T.
> Erwin's Piano Restoration Inc.
> Mason & Hamlin/Steinway/U.S. pianos
> www.Erwinspiano.com
> Phone: 209-577-8397
>  
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love
> Sent: Friday, September 21, 2012 7:52 AM
> To: pianotech at ptg.org
> Subject: Re: [pianotech] Action Ratio measuring
>  
> Using my Renner action model I made the following measurements and calculations using both methods and this is what they yield.  While the exact point of measurement on using Del’s method, especially at the knuckle jack contact point, is difficult to be precise on and can be interpreted differently, there’s no question that even with the range of possible measurement points that method yields a lower number, too low, in my opinion.  When I calculate the action ratio by displacement, key travel versus hammer travel, the result is as you see below.  It should also be noted that with the displacement method the actual travel should be measured as the length of the arc segment and not the secant line that connects the two points (low and high) in a straight line.  Thus, the ratio using that method would be slightly understated.  That agrees more closely to the method I’ve suggested and is part of the reason that I use it.  I urge those with an action model to test the findings on their own. 
>  
>  
>  
>  
> Del’s method
>  
> Ea
> Ra
> Ratio
> Key
> 265
> 134
> 0.51
> Wippen
> 66
> 94
> 1.42
> Action Ratio
> Shank
> 22
> 142
> 6.45
> 4.65
>  
>  
> My method
> Ea
> Ra
> Ratio
> Key
> 260
> 128
> 0.49
> Wippen
> 62
> 100
> 1.61
> Action Ratio
> Shank
> 17
> 127
> 7.47
> 5.93
>  
>  
>  
>  
> Measured by displacement.  6 mm of key travel yields 35 mm of vertical hammer travel 6/35 = 5.83
>  
>  
>  
> David Love
> www.davidlovepianos.com
>  
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Delwin D Fandrich
> Sent: Thursday, September 20, 2012 12:10 PM
> To: pianotech at ptg.org
> Subject: Re: [pianotech] Action Ratio measuring
>  
> I use the measure points because they make the most sense to me—I've no idea how they correlate to those used by others. The most wear on a key takes place about 20 mm back from the front of the key so I assume that is where most pianists strike the keys most of the time. So that is where I start my measure. The next lever goes from the balance point to the center of the capstan. Then from there to the wippen flange center. Then to the tip of the jack where the jack contacts the knuckle. (Yes, I know the force goes first to the jack center but if you study the action model....) And then from the knuckle center to the hammershank center and from there to the tip of the hammer. Anyway, those are the points I use.
>  
> The longer the lever the less absolute accuracy matters. I usually try for the nearest half-mm. Sometimes I settle for the nearest mm.
>  
> It's easier when you are designing an action and key set—you can take it out to 14 decimals on the computer screen if you want. Not that that makes any real difference in the real world. And you don’t have to go through any contortions to get your measurements.
>  
> ddf
>  
> Delwin D Fandrich
> Piano Design & Fabrication
> 6939 Foothill Court SW, Olympia, Washington 98512 USA
> Phone  360.515.0119 — Cell  360.388.6525
> del at fandrichpiano.com — ddfandrich at gmail.com
>  
>  
> -----Original Message-----
> From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Brown, David
> Sent: Thursday, September 20, 2012 11:48 AM
> To: pianotech at ptg.org
> Subject: [pianotech] Action Ratio measuring
>  
>  
> Del, David and all-
>  
> Huge thanks for the completeness of these explanations and  examples. Del, the pdf was very clear. I am on a Mac, so bins  and the like come out wacky. I do notice from your example that this is yet a third way to measure key in, from balance point to front rail pin. How fussy are these in practice? Do the relationships remain constant? It would not seem so. +/- a mm? More ? Less? Thanks for all for taking daytime for this. It will take a while to digest.
>  
> Best-
>  
> David

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