[CAUT] Moving the Wippen Rail.

[James Ellis]

I have been reading the mail re moving the wippen rail back to change the
action geometry to lighten the touch.  It was not my intention to get
involved in this discussion, but I see that confusion persists, and I would
like to help sort it out, if possible.  I don't remember exactly who said
what, and it doesn't matter.  Argument is not my objective.

Moving the wippen rail back increases the distance from wippen center to
capstan contact.  It also decreases the distance between capstan contact
point and jack center.  If the jack were perpendicular to the wippen, and
if the hammer shank were perpendicular to the jack and parallel to the
wippen, the very slight change in the angle of the jack would be
irrelevant, and the ratio change would simply be that caused by the ratio
change of the wippen.

But that's not quite the way it is.  The jack is at an algle to the wippen,
but perpendicular to the hammer shank.  When the jack is realigned to the
knuckle after the rail has been moved back, its angle to the wippen will be
changed.  If we are going to be exact about this, we will have to figure
the cosine of that angle in each case, and subtract one form the other to
find out how much the change in jack angle actually makes to the leverage.
We will find that it is some, but not much compared with the simple change
in wippen leverage.  Another way of looking at it is to compare the
distance from wippen center to capstan contact against the distance from
wippen center to jack contact with the knuckle.  I think this is what Ric
B. is talking about, but I'm not sure, and I don't want to misquote
someone.  That's a good approximation, but it's not accurate either,
because an imaginary line drawn from hammer center to wippen center does
not intersect the jack/knuckle contact point.

If we are going to be really fussy and exact about this, we will have to
solve for a bunch of angles and lever arms to know just how much difference
it does make.  

However, something more inportant is being overlooked here.  If the wippen
rail is moved back, and the jack realigned to the knuckle, the jack's
clearance at the front of the balancier window is going to be reduced.  If
it is critical to begin with, and it should be for maximum repetition, then
the new position will cause the jack to hit the window cushion hard on a
hard blow, perhaps breaking off the tender.

There have been a few times when I have moved a wippen rail, but those were
only after careful measurements told me it was in the wrong place to begin
with.  I have never done it merely to change action geometry.

Sincerely, Jim Ellis