[CAUT] stack fit to keyframe

[Bob Hohf]

I'm afraid I can't describe briefly an idea that took a 4-article series to
develop.  I would at least have to reread the articles to see what I said
then, and suspect that I might not agree with all of it now.  We all agree
that action geometry is complicated, there is more than one approach to
every problem, and different approaches can indicate different solutions.
One must decide which set of action parameters to use as guides and follow
through to solutions.

Here's what I take as given:
1.the elevation of the key bottom at the balance rail, since this is not
easily changed.
2.the geometry of the action parts, at least with such high quality pianos
as S&S etc, since they have been proven for generations to work superbly if
properly configured.
3.the factory hammer bore spec.  However, in practice I change the bore to
accomodate special cases, such as a plate casting that doesn't allow a
consistant string height. I believe changing the bore length more than a
little can have a big effect on the mechanics of the swinging hammer.
4.the "magic line"
5.I think that in the article I mention having the centerline of the hammer
perpendicular to the string when striking.  This is debatable, and in
reality is almost never the case.  However, awareness of this parameter and
controling it is a good test of your rebuilding ability.
5a. I do aim to have the hammershank parallel to the keybed when striking.

Using an action model modified to make the wippen and hammershank centers
adjustable, I varied them, graphed it out and determined that optimizing
this set of parameters specifies a single optimum string height. I suppose
choosing different parameters might indicate a different height.  I have
never explored this idea and am unlikely to unless someone wants to finance
the research.  If you are rebuilding the piano, you have control over the
string height.  So you can set it at the elevation where all of the
parameters are optimized.  There is only one such elevation.  If you are
doing only action work on a piano, you're stuck with the string height
whether it's right or not.  If not, something has to give.  In this case I
take up the slack at the magic line.  One can't argue that the principles
calling for the magic line are correct, but in reality I've never been able
to detect an increase in friction in an action that deviates from the magic
line.

How much difference this sort of thing makes is hard to say. I'm not
necessarily recommending that anyone adopt this sort of approach.  If you
consider the question, "Which makes a better result, good theory or good
execution?", my answer would be good execution.  All the theory in the world
behind a plan doesn't matter a fig if you can't accurately execute the plan.
Of course, good theory _and_ good execution always wins hands down.  If you
study actions closely enough to measure parameters accurately, and develop
an understanding of the relationships between them, your action work will be
better regardless of the particular set of parameters you choose.

Bob Hohf

>
> >...The main point of the series was that for a given balance rail
> >elevation, there is a single optimum string height for an action.
>
> Bob, I'm afraid I don't have access to your articles.  I wonder if
> you could elaborate a little on this statement.  It seems to me it
> could only be so for a certain design of action and given a certain
> hammer-bore length.  Even then I would need to verify whether what
> you say is so, since the idea had not occurred to me.
>
> JD
>
>
>