action ratios

[Stéphane Collin]

Hi David.

I plan to do a more in depth study of your metrology.  Maybe I sould not dare to jump into this discussion before that.  But isn't there a certain analogy between ratios given by geometry, and ratios given by weight comparing ? If difference exists, could you explain that ?

Best regards,

Stéphane Collin.



----- Original Message ----- 
From: "David C. Stanwood" <Stanwood@tiac.net>
To: <pianotech@ptg.org>
Sent: Saturday, November 02, 2002 3:51 PM
Subject: Re: action ratios


| Dear Stéphane & Friends,
| 
| I see some confusion in the discussion about what ratio is.  This is my
| view: When we talk about touchweight we refer to weight ratios and in this
| regards we refer to strike weight ratio which is the amount of weight, at
| the front of the key, that it takes to balance a gram of weight at the
| hammer.  When we talk about geometry we refer to distance ratios which is
| the distance the hammer moves for a given unit of distance at the front of
| the key.   Stéphane shows an analysis with mixed types, some touchweight
| and some geometry.  One or the other please! 
| 
| The discussion that we have been having is about strike weight ratios
| unless said otherwise.  The calculation 
| of strike weight ratio is found by determining the Top Action Balance
| Weight which is front weight plus balance weight.  It's the total upward
| force at the front of the key from the hammer/shank & wipppen.   From this
| we subtract the Wippen Balance Weight which is the Wippen Radius Weight
| times the Key Weight Ratio.  The result is the Strike Balance Weight or the
| upward force at the front of the key resulting from the weight of just the
| hammer/shank.  Divide this by the strikewt and we have the strike weight
| ratio.
| 
| I would like to offer a more direct way of determining strike weight
| ratio... a "Short Cut".  It also might help some to understand conceptually
| what it is.... 
| 
| Short cut method for determining Strike Weight Ratio:
| 
| 1. Make sure the key bushings are free and lubricated with try Teflon powder 
|    (generally recommended whether or not your taking this measure)
| 
| 2. Make a platform jig that may be mounted on the back of the key for
| holding temporary weights:
| 
|    http://www.stanwoodpiano.com/ratioshortpic.jpg
| 
| 3. Flip up the hammer and put key leads on the platform at the back of the
| key:
| 
|    http://www.stanwoodpiano.com/ratioshort.jpg
| 
| 4. Put key lead weights on the platform jig and arrange them so the
| key/wippen are zero balanced.  The key is zero balanced when you throw the
| key down so it bounces back to center and when you throw the key up it
| bounces down to center in a like motion.  If the motions are different then
| move the weights until the motion is the same in either direction.  You can
| also use a gram gauge and move the key up and down at the front.  When the
| scale readings are the same in either direction the key is zero balanced.
| If the key has no keyleads in it then you can probably use a small keylead
| at the front end of the key without using the platform.
| 
| 5. Flip the hammer/shank down and leave the temporary weights on the back
| of the key.  The weight at the front of the key is solely from the hammer
| and shank as the key and wippen have been zeroed out of the equation.
| 
| 6. Measure Up/Down and calculate the Strike Balance Weight (D+U)/2.
| 
| 7. Divide the Strike Balance Weight by the Strike Weight to find the Strike
| Weight Ratio.
| 
| Measure at least six samples to calculate an average level of SBW.  I
| recommend notes 16,17,40,41,64,65 to get a sampling across the most played
| parts of the keyboard.
| 
| Hope this helps...
| 
| David C. Stanwood
| 
| 
| 
| >> 5 mm dip gives an average 25.5 mm hammer rise (linear, not
| >> angular, but anyway I couldn't achieve a precision
| >> measuring so this matters).  I assume this is a 5.1 ratio action.
| >>
| >> Sorry for WW and FW, but this piano is in very last stage
| >> of rebuilding, and waiting for customers, so I'm not about
| >> to pull the stack out of it now.
| >>
| >> But I measured KR through length between balance point and
| >> front key, just above the front pin (243 mm) and length
| >> between balance point and whippen center for the rocker leg
| >> (no capstan on older Bechstein) (140 mm).  This should give
| >> us a KR of 140/243 = 0.576
| >>
| >> Here are the other measurements
| >>
| >> note   DW    UW    SW
| >> C-3   60      40       8.4
| >> C-2   60      39       8.4
| >> C-1   63      47       8.9
| >> C0     62      39       8.3
| >> C1     57      36       7.3
| >> C2     56      35       6.5
| >> C3      56     32       5.8
| >>
| >> What do you think ?
| >>
| >> Greetings, and much respect.
| >>
| >> Stéphane Collin.
| 
| 
| 
|    
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