[CAUT] Digest, Vol 1103, Issue 85 Moving Wippen Rail

[David Love]

I'd have to agree with Keith in all this.  While aligning the jack 90
degrees to the shank is not unimportant, there is some tolerance and it's
seen frequently when converting original dimension Steinway's to 17 mm
knuckles.  The friction at the jack is not even seen in the measured
touchweight since the knuckle rests on the balancier.  The only friction
change might be during the let-off stroke and even then, at let-off, the
angle of the jack relative to the knuckle would have rotated through 90
degrees to the shank anyway.  If someone is seeing a change in measured
friction by aligning the jack differently, they should look elsewhere for
the answer.  Having the capstan/wippen heal interface properly located on
the magic line is a different thing altogether since the degree to which it
is misplaced will contribute to less efficient lifting and more sliding and
thus in increase in friction.  When moving capstans or shimming out wippen
rails (or choosing straight versus slanted heal wippens) attention should be
paid to where the capstan/heal interface will fall with the new parts and
they should be selected accordingly, not based on what was there to begin
with.  

 

Unfortunately, rebuilding actions without making new keysets is often a
series of compromises.  In terms of priority, jack/knuckle angle is lower
down on the list that other things I can think of.  As I said, it's not
unimportant, but neither is it the most important.    

 

David Love
davidlovepianos at comcast.net
www.davidlovepianos.com 

-----Original Message-----
From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of Keith
Roberts
Sent: Tuesday, October 30, 2007 6:36 PM
To: College and University Technicians
Subject: Re: [CAUT] Digest, Vol 1103, Issue 85 Moving Wippen Rail

 

 

On 10/30/07, Richard Brekne <ricb at pianostemmer.no> wrote: 


In anycase, moving the whippen rail is a matter of creating this
alignment and not a matter of changing touch weight. 

 

Sorry Rick but that doesn't agree with the data. The action I was just
working on Dale weighed off yesterday and he had been trying to squeak an
extra lead out of the keys. It was weighing off with 4 leads in the bass
when regulated. After the rail move it weighed off with 3 leads. This is
because the resistance arm when measured to the top of the jack is not a
direct ratio to the effort arm. The force has to be translated through the
jack first. Remember weigh-off is only to let off so miss alignment of the
core to the knuckle core will make no difference as long as the jack is
pointed at the center of the knuckle. 

 

So to figure the force directed out the jack, you make the line from wippen
center pin to the jack center pin the x axis and then the tangent line is
the y axis. By the number of degrees you calculate the amount directed back
down the x axis and then you figure the resultant force vector directed down
the jack. Then resolve the force at the end of the jack to the tangent line
of the arc from the top of the jack to the wippen center pin. There will be
a slight movement of the magic line but when 2 mm is translated in degrees
back to knuckle it is nothing. 

 

In any event like David Love said and what my mentor thinks agrees with the
data: there is a change in the amount of weight needed to balance an action
and there is no measureable change in friction. Personally I don't see how
you can change the effort arm of the wippen and not effect a change in
leverage. 

 

That's my story and I'm sticking to it.

 

Keith Roberts

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