[pianotech] key position at rest

[Jon Page]

>Sorry I don't quite get it ... but  1 1/2 inch from where ?  From 
>exactly what point
>on the whippen to exactly what point elsewhere does this 1 1/2 inch 
>come from ?

 From the key bed. Generally a S&S will have the key end lifter felt 
at rest at ~1 3/8"
from the key bed and the underlever at rest is around 1 1/2" from the key bed
which is lifted by the key to around 1 3/4" from the key bed.

As an aside, knowing the height to which the underlever is lifted allows
you to determine if the underlever is situated at an optimum angle.
Measure the height of the end felt with the key depressed. Lift the front
of the underlever to that measurement and notice the lever's angle relative
to the key bed. If it is parallel, that is ideal. If it is still 
angled down then that
indicates that the lever is scrubbing too much on the felt (increased friction)
and there is probably a trough worn into the felt.
Lifting beyond parallel is counter productive as well.

I think it was in the same class (involute gear) with Chris Robinson
that he drew a chart with an x and y axis. Friction is minimal along each axis
but as you migrate further into each quadrant, the friction increases.

So looking at the underlever as being dropped down from the horizontal x axis
with the center pin on the y axis, it makes sense to lift it to a 
point of least friction
(x axis) which also happens to be the point of Let Off at the end of 
the key stroke.

This is why I reset the tray pivot such that the underlever is lifted 
to parallel
to the key bed or to the x axis. Lifting beyond parallel crushes the corner
of the felt and reintroduces sliding friction (getting into the upper 
quadrant).


>...capstan angle...why is the standard today then perpendicular to the key ?

Ease of installation. Mark a point under the cushion, drill them straight in;
no need to waste time fiddling around with an angle.
-- 

Regards,

Jon Page
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