[pianotech] capstain/wippen angle, was: key position at rest

[David Love]

I'm not sure about this.  There is no sliding if both parts move exactly
vertically, right?  Of course, they don't, they both move in an arc.   So,
for example, the higher above the magic line the capstan starts the more a
line tangent to the scribed arc will be tilted toward an angle horizontal to
the keybed and since the wippen moves in an arc opposite to that (since the
flange is on the other side of the capstan) there will be more sliding.  All
you can do really is maximize the period at with the line tangent to both
arcs (wippen heal and capstan) are parallel or at least ensure that in the
arc movement those lines reach parallel at some point.  Perhaps it doesn't
matter if they achieve that parallel position at the beginning of the stroke
or at the end or, for that matter, in the middle except that the farther off
the magic line you go, the greater the difference in angles of those tangent
lines and so the greater the sliding.  So it seems to me that having the
travel begin and end an equal distance from the magic line would minimize
the sliding.

David Love
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Ron Nossaman
Sent: Sunday, March 15, 2009 11:03 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] capstain/wippen angle, was: key position at rest


It strikes me that a good starting place is basic geometry, 
with the changing total distance from wippen center to balance 
rail hole via capstan contact point. If you start with the 
contact point below the magic line and end up with it above, 
that total distance changed from longer to shorter, to longer. 
If you set the contact point at the magic line at either the 
top or the bottom of the keystroke, the length change is one 
way. With the magic line centered in the stroke, how it it 
possible to maintain non sliding contact with the direction 
reversal? With the contact point not passing *through* the 
magic line, it very likely is.
Ron N