[pianotech] Action Ratio measuring

[David Love]

One other comment, to avoid any discrepancies from the finger contact point
on the key question, I've taken both sets of measurements to the end of the
key.  

 

David Love

www.davidlovepianos.com

 

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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