Action Geometry

[Jon Page]

talAt 12:05 AM 08/20/2000 +0200, you wrote:
>Had another question on this Stanwood stuff.   grin.. I hope I get a few 
>more responses then my last....:)
>
>Ok.. so you have this basic Equation for balance and a bunch of charts for 
>different Strike Wt vs Strike Wt Ratios.  These differ depending on what 
>Balance weight specs and all have the same Whippen Balance Weight specs. 
>These then represent "givens" for the equation of balance.
>
>I am wondering then if you can do the following:
>
>After makeing sure of correct action spread and confirming correct capstan 
>position and height for that spread, pick the strike weight ratio you 
>want, and balance weight spec. and then establish the corresponding strike 
>weights for the hammers. Adjust the whippen radius weight so that together 
>with the actual key weight ratio (dependent on the capstan position) you 
>get a match to the spec for the whippen balance weight. That gives you all 
>the numbers for the equation except the Front weight, which of course you 
>can solve for with these numbers. After solveing for FW, install weights 
>in the keys to match the solution. Now it seems to me that what ever 
>discprepency there is in the resulting real balance weight, and the 
>specified balance weight would be due to friction. And that you should be 
>able to adjust by dealing with the action centers and key bushings.
>
>Relocating the capstans would seem only to be neccessary if  the whippen 
>balance weight spec is too difficult to obtain, and if you cant achieve 
>correct whippen travel distance when the height of the capstan interesects 
>the magic line.
>
>This seems like kinda simple really,,, so obviously I am scratching my 
>head wondering what I am overlooking... grin..
>
>--
>Richard Brekne
>RPT, N.P.T.F.
>Bergen, Norway
>

I'm scratching my head too, I think you're thinking too much. Might I 
suggest that you get an action and start
playing with the variables to understand their inter-relationship. Then get 
another one, then another. You have
a lot of theory which needs some practical application. Nothing beats 
hands-on experience.

An action model is fine for comprehension but it takes an actual problem to 
put yourself to the task of its
resolution. Each action poses a different need. After about ten actions it 
will start to become less perplexing.

Friction does not affect BW to the degree that it affects UW & DW. Extreme 
friction will contribute to a higher BW
but generally BW is derived by weight and counter-weight. Once BW is 
established, friction establishes UW & DW.
Survey some keys, reduce the friction (repin, ease keys) and  resurvey; see 
what happens. Balance Weight is
centered on these two factors, friction determines their spread and 
'weight' determines the BW position on the scale.

Once, I had a difficult time pinning down the friction. It turned out to be 
loose knuckle covering. The buckskin was
actually slipping around the core. I bolstered the backside so as not to 
disturb the contour but to tighten the cover.
it dropped the friction between 2 to 6 grams.

And don't pay such close attention to the Wippen Balance Weight. It is not 
important. Once you get into it up to your
elbows you will see what the important factors are.

Get busy :-)



Jon Page,   piano technician
Harwich Port, Cape Cod, Mass.
mailto:jonpage@mediaone.net
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