Capstan Angle

[Jon Page]

I'd like to add my slant to this discussion.

Repeatedly, time and time again, I've corrected regulation problems
(insufficient after touch) by decreasing the angle of the capstan without 
altering KR.

Let me reiterate again how I establish the capstan's attitude.   Mark the 
edge of the wippen
cushion  at the magic line and draw a line through that mark perpendicular 
to the cushion
onto the key side (action blocked at half-blow).  A capstan installed at 
that angle will have
the angles at rest and full dip to be quasi equal and opposite, moving 
through perpendicular.

One way to lock the action at half-blow is to prop a tri-square (with a 
spring clamp)
set to the appropriate height to block the hammer and place a weight on the 
front of the key.
Another way is to shim underneath the weighted key front.

Many times an acute capstan angle will not move the wippen through 
sufficient distance
to achieve adequate after touch. These 16+ degree angles when decreased to 
~3 degrees
without altering KR can produce a system which causes the action to 
function properly
without having to compromise hammer blow or key dip. Once or twice it meant 
a slightly
forwards facing capstan.

It could be too that it's the face of the capstan, which is now more in 
contact with the cushion,
imparts lift across a broader surface (closer to the wippen center).

Once the angle has been established, the position of the capstan can be 
moved fore and
aft slightly to fine tune after touch.  For any given set of key dip, 
hammer bore/blow, knuckle
radius there is an optimum KR which causes the wippen to move through 
sufficient distance
for the jack to clear the knuckle. Too much KR and you'll be decreasing dip 
and/or decreasing
hammer blow, too little KR and you'll be increasing dip and/or increasing 
hammer blow.
The Goldilocks Principle.

Regards,

Jon Page