the magic line

[Robin Hufford]

Hello Quentin,
     This should be referred to by its correct name, in my opinion, as
it sounds less unprofessional,  which is the line of centers.
     Consider a rotating tire, or two,  - it rotates around the
centerpoint of the wheel just as the whippen rotates around the whippen
flange.   If you had two tires they could not be brought any closer
together, and travel on one another, that is, run on one another than at
a point on a line joining their two centers.  This point on the line is
just where the two radii line up.  The common tangent to the wheels  at
this point is where the two tires can contact each other with the least
friction.
     The key is rotating around its center at the balance rail pin
hole.  A line joining these two axial points - the center of rotation of
the key at the balance rail hole, and the center of rotation of the
whippen at its centerpin,  is the so-called "magic line".  Since the
whippen is sliding on the capstan and cannot actually be maintained at
this point,  the amount of friction this sliding produces can be held to
a minimum if the line of approach is equal to the line of recession,
that is, the glide path of the capstan/heel interaction is distributed
equally before and after the point of common tangency when the key is at
half travel.
     This consideration defines in general,  the layout of a well made
action, for example, many of the high-quality American actions of the
past.  Although the line joining the centers of the key and whippen
rotation gets the most play, others exist.  On a grand piano, the line
from the whippen flange center to the point of contact of the tender on
the let-off button at let-off, should be approached by the jack flange
and, ideally, should be distributed about this line just as is the
whippen heel/ capstan, and, for exactly the same reason.
     Similarly, the line from the whippen flange center to the hammer
flange center.  At let-off the knuckle/jack contact  should be passing
somewhere along this line, again, for the same reason
     As Ron O. mentions the repetiton lever/knuckle contact should,
again, be treated similarly so that its motion of approximately
distributed on the line from the whippen flange to the hammer flange,
and I don't believe this indeed is an insignificant consideration.
     This continues on into the underlever system  and dampers,
particularly which the underlever/key contact point.
     Even though one sometimes finds compromises in some of these
considerations, in general, in my opinion, any number of high-quality
actions can be found, from the past, to have been laid out so.
Regards, Robin Hufford

>    Part 1.1    Type: Plain Text (text/plain)
>            Encoding: quoted-printable