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
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