[CAUT] Moving wippen rail

[Paul Chick]

It would be a tremendous help to us reading these posts if you "posters"
would spell out the words for "EA"

"W" "RA"  etc.  Many of us would like to understand the Stanwood language,
and maybe take his classes to learn how to apply it.

Thanks in advance to my learned brethren!

 

Paul C

Subject: [CAUT] Moving wippen rail

 

I'm not the only one confused by the facts contradicting the predictions
made by using the action ratio of the wippen measured to the top of the
jack.

 

Gene Nelson of the the Sac chapter wrote this. 

 

Had to get out my Renner action model.
At 111mm action spread - blow is 1 3/4 key dip is 9mm and downweight is 80
grams (no key leads in this model)
At 113mm action spread with 1 3/4 blow there is not enough key dip (at
9mm)to get let off and downweight is 77 grams. 
I still have a hard time picturing how leverage changes because the whippen
ratio stays constant as measured from key capstan to whip center pin and
whip center pin to jack knuckle interface. Moving whippen in or out
increases or decreases both dimensions equally and the ratio is unchanged. 
--------------------
RPT
PTG Member
 

I wrote this:

 

Gene, I just had this discussion on CAUT. The claim that measuring the ratio
to the top of the jack is erroneous in my logic. If you do it that way, I
can show you models where the force at the top of the jack is the same for
different ratios when measured that way. It doesn't allow for that. The
force at the the jack/knuckle depends on the EA of the lever and the RA.
Wcenter pin to capstan is the EA and Wcenter pin to jack center pin is the
RA. Then the force delivered up the jack changes in relation to the angle
the jack takes to the tangent line of the RA arc. So you figure the
difference in the output at the jack by the number of degrees the jack moves
and not by the distance the top moves. Jacks can be of any length and so I
can give you any action ratio you want by measuring that way. So long as you
don't change the jack angle much, the force won't change but if you change
the length of the EA and get out of your head that you measure to top of the
jack and measure to where the force is applied, the jack center pin, you see
the the RA is fixed and the ratio changes. 
The force at the jack pin changes and any idiot can see that the force at
the pin is the same as at the top of the jack. The slight change of degrees
to the tangent line does not change the force equally to the change in
leverage of the the wippen. 

When measured my way it works but mine is not a true way of gaging the
action ratio either. The action ratio essentially is a tool to find if you
are centered in the action leverage sweet spots. How you measure it doesn't
change what it is, it only shows you where you stand. You adjust things
until the action ratio looks good the way you measure it. I look at it from
both views because force transmitted can change differently than the actual
distances moved will change. 

--------------------
Keith Roberts
Associate, PTG
Keith's Piano Service
Murphys,Ca
 

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