Kawai let-off (poor jack design?)

[Richard Moody]

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> From: Ron Overs <sec@overspianos.com.au>
> To: pianotech@ptg.org
> Subject: Re: Kawai let-off (poor jack design?)
> Date: Thursday, May 06, 1999 8:56 AM
>. Check out the additional down weight required to push a typical modern
action jack through >let-off (ie. a jack with a smoothed and slip coated
tail and roller contact surface); it will >typically require 150 grams.
Prototypes of my new jack, which we recently manufactured >(installing
them into a rebuilt Kawai KG6), required a down weight of 125 grams to
execute >the >let-off.

I have always been interested in the additional weight needed to push the
jack through let-off. You say it will require ADDITIONAL 150 grams.?? 
Perhaps you mean milligrams? Centegrams? 15 grams?? The problems I have
had is the momentum of the 54 gram weight carrying the key though letoff
or only to letoff when placed on the key at rest. So  a "feel" of the
friction of let-off (rather than weight measurement) has always guided me
in evualtion of touch in that area. Not too scientific, but at least the
player and I can focus on that if necessary through sensation of finger
pressure. (I was taught the distance of after touch determined the feel of
"touch" if the down weight was with in range, and that is different
according to player preference)

> Our new jack design is part of an overall redesign of the grand piano
action. Recent >prototypes, with the down weight set at 54 grams, have
yielded up weights in excess of 40 >grams. If this translates to real
world factory piano actions, friction figures of less than 9 >grams look
to be achievable.

I have recently wondered why factories have never published "optimal
upweights" That should indicate  "friction".
Carrying it out further I am wondering why there are not up and down
weights given for dampers at rest and then for dampers raised.  

Ric Wondereder