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 > > >
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