Kawai let-off (poor jack design?)

[Richard Moody]

OK I have a Kawai wip. And I am examining the motion between the jack
tender (heel) and substitute let off button.  Why is it gouging a groove
in the let-off button felt?  Because of its lateral motion across it, or
the impact?  What is in this design that makes this wear more in Kawai
than other designs?  
	I don't know if there is a let off button in any piano without some sort
of depression from the jack heel (tender)  AND it is the postiton of this
depression (groove) that determines the fine regulation of let off.  I
know it is frustrating that the let off button must be turned in
increments of 180 degrees. (Or 360 if it is not centered over the heel),
for "wide" heels.  On the other hand for "narrow" heels such as the Kawai,
these impact less surface area on the button so perhaps give a "high heel"
effect to the felt, ie a deeper groove.(or so one would think)  Either
way, once you start "regulating" it seems  a lot more is needed a lot
faster, because, (I tink) you are giving the tender a fresh soft surface
to dig into.  Do you mean a better design would prevent this?   Details? 
Because of the "circle of actions" don't you think it is impossible for
one circle to move across a stationary object without rubbing, therefore
gouging ?  If that is all the jack tender had to do.  Poor thing, it seems
to be moving in two directions at once! 

 Ric Greuve






----------
> From: Ron Overs <sec@overspianos.com.au>
> To: pianotech@ptg.org
> Subject: Re: Kawai let-off (poor jack design?)
> Date: Wednesday, May 05, 1999 2:59 AM
> 
> 
> The geometry (ie. built in friction) of the KG jack at the let-off
button 
> is one of the best examples of poor action design in the business.
> 
> Try mounting a wippen on the workshop bench (hold it horizontally by 
> clamping the wippen flange onto a support block), substituting the 
> let-off button with a plain wooden dowel (also held horizontally).
> Examine the relative motion between the jack tender and the let-off 
> button during escapement.
> 
> And how does the KG let-off button cloth survive under real life
service? 
> It doesn't! As the jack tender gouges a groove in the felt  the let-off 
> setting moves toward the string.
> 
> Ron E. Overs
> Sydney, Australia
> 
> 
> Email: ron@overspianos.com.au
> Website: www.overspianos.com.au
>