Science

[Michael Wathen 556-9565]

Isolating a variable is still an important method.  It is
particularly important for us technicians who want to clarify
some things for themselves.

Some of us may remember an exchange that took place between
several of us about the effect of changing the knuckle size.
Vince made a claim that reducing the knuckle size would lower the
Downweight.  I countered back that my experience leads me to the
opposite conclusion.  Vince then stated that he had done this
operation for an entire piano and that was how he had come to
this conclusion.

My own private reaction was to drop it.  However, I have in my
shop a Pratt and Read action model.  I use this model all the
time when I have a question about what the effect of a certain
change might be.  I can change one thing (isolated variable) and
watch what happens.  Because I made no changes to anything else,
I was left with a rather large degree of certainty about this
relationship.  I had performed this type of investigation before
on the relationship between Downweight and the distance of the
action arm at the hammer shank center.  The action arm is the
distance from the center pin of the hammer shank to the point
where the jack contacts the knuckle.  I found that this distance
is proportional to the measured Downweight.  Increasing the
distance lowered the measured Downweight.  As you can see making
the knuckle smaller would decrease that distance and would
increase the Downweight. Exactly the opposite of Vince's claim.
I also knew that what I did was <repeatable>, any Joe Blow could
do this simple experiment and come up with the same thing.  So
when Vince made his claim that he had done it and it had produced
a lower Downweight, I had no doubt that he was telling the truth
but I did doubt that the result come from where he thought it
came.   I just figured that he had probably changed several other
things also.  Who knows had he replaced the hammers, whippens,
rebushed the keys, or VJ Lubed the key pins?  We often rebuild a
piano from the bottom up, but again who knows if it was the
hammers, soundboard or bridge that was responsible for most of
the change.

I think that this discussion about science is long overdue for
piano techs.  I would also highly recommend an elementary Physics
class for anyone interested.  Many of us work in universities
that offer free tuition.  That's what I did.  I was a university
technician long before I had any idea of what Newton's Laws were.

Michael Wathen