action ratios

[Isaac OLEG]

David,

Thanks very much for this fast SW method, I used it today, fast,
simple, and efficient.

On the piano I tested (little old 1.50 grand) I used a gram gauge to
check the evenness  'zero balance" of the key, and indeed it was
moving in the 1 -1.5 g range maximum.

Beside, it seem not too hard to obtain the correct balancing by feel
and observation.

I've find , as expected on this one, a 5.8 SW ratio on the whites,
while the sharps where 6.2 6.25. The results look correct. While a
direct linear reading gives slightly less high figures. But on this
action, the sharps have a KR too different of the whites, the capstan
is way too high, so I had to move things in many directions to help to
lessen the difference.

I understand that direct measurements show slightly different results
than weight based, as the friction varies during the stroke depending
of the geometry, as the efficiency of movement transmission at the
capstan/whippen contact. How do they vary and in what direction I
don't know.

But having problems shown by the weight method, then confirmed by
direct measurement, then corrected, then evening the corrected action,
seems to me a very valuable approach.

Was thinking of the use of cardboard punching, not too thick but cut
on the front, to help the beginning of the move of the sharps (as an
artifact, but it may work actually).
I noticed too that even with heavy parts, having a good geometry gives
us a window for regulation that lend to an enjoyable piano sometime
even when many things are in the way .

Thank you again, and Regards.

Isaac OLEG




> -----Message d'origine-----
> De : pianotech-bounces@ptg.org
> [mailto:pianotech-bounces@ptg.org]De la
> part de David C. Stanwood
> Envoyé : samedi 2 novembre 2002 15:51
> À : pianotech@ptg.org
> Objet : 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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