Action Geometry

[Richard Brekne]

Hi guys... Thought I'd return to this line for a bit. Recently been getting
more and more involved in Stanwoods approach to things and a few questions
have popped up that I'd like some opinion on.

You may remember a couple weeks ago I had some questions about front weight
on a Howard grand. Stanwoods answer to my weight measurements was basically
that the capstan had to be moved... grin, I never did get a straight answer
from him about whether or not I was correct in assuming that I needed more
front weight.. but thats another story. I was a bit miffed at how he could
declare from the numbers that the capstan needed moving.

Since then I have looked into things a bit closer and have the following
observations and questions.

It seems to me that Stanwoods approach is what I will call a  "weight
priority" approach. That is to say that certain component weighting factors
can take precedence over geometrical concerns. Now many of us have learned
a bit about action spread, and that knowledge tells us that once the spread
between the hammer rail and whippen rail is set, then the capstan height is
a given for any position the capstan occupies along the length of the key.
Further the capstans position must be such that at proper height, it must
move the whippen upwards  (for a given key dip) such that the jack just
clears the knuckle at letoff height. Optimum whippen movement lets call
that... grin..

Ok... So how much fudging in geometry can we allow for in order to create
specified weighting conditions as called for by any given Stanwood design
??. I have heard tell of capstans having to be moved as much as 10 mm and
it seems almost incredible to me that the factory can be THIS far off on
such an essential factor. Shouldnt any touchweight design absolutely HAVE
to rely on basic action spread geometry ?

There are like three major concerns.. Distance leverage, Weight leverage,
and Action Geometry. It almost seems like Stanwoods approach disregards all
but Weight leverage. I assume this is because it is figured that if the
Weight leverage is at specs, then the other two factors will be within an
acceptable range.

In the action I had a couple weeks ago, I checked action spread pretty
closely. I perhaps could have fudged abit in the direction of making the
spread just a tad wider. But really, the jack to knuckle relationship with
the hammer at rest was just fine. Hammer rest height was good as well.
Moveing the capstan to meet any given Stanwood spec, would entail also
moving the whippen cushion. These adjustments are going to affect the
whippen travell distance, and again,,, capstan height has to be set so that
its contact with the cushion intersects the so called magic line... so it
seems to me there are potential problems here.

Wouldnt it be better to set and confirm optimal action geometry, and adjust
weighting to fit ?? One could still use the Balance equation as given by
Stanwood, but its application would have to be somewhat different.

I would appreciate your thoughts on all this.

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway