Dale wrote: > Ron > I just wanted to say publicly--Thanks . This is a great clarifying > summary. Clarification is always enlightening. Your post also points out > that "the confusion that remains is still how all this stuff > mechanically relates" which is true. At the end of the day we have to > put all this into a useful sytematic practice in rebuilding the actions > we all work on.These discussion increase our confidence secure better > results for us & perfromance benifits for our clients. Dale, Several people have complained that this material has just brought more confusion to our understanding of the grand action. That's understandable since the study of the dynamic action is at least ten time more involved that studying the static action. It took many years for the simple static principles Stanwood has developed to be accepted and understood. I would expect these dynamic principles to take a lot longer. The task is especially daunting since getting a mental grasp of how it works requires familiarity with math and physics. I expect that most piano technician's would need to bone up on high school level algebra and physics to gain access to this knowledge. Even though this is going to be a lot of work, as you said, it can be accomplished one step at a time. The first step is getting the notion of moment of inertia clear in ones mind. Envision a cylinder attached to an axle with a rope wrapped around it. We pull on the rope and the cylinder rotates around its axle. If the cylinder is made from a light material like wood, it is easy to pull the rope. If it is made from a heavy material like steal, it will be hard to pull the rope. The moment of inertia describes how hard it is to pull the rope and get the cylinder to move. Knowing the MOI of the cylinder and the radius we can predict how hard it is to move. We can also know how much tension there is in the rope. With a high MOI the tension is high and with a low MOI the tension is low. "What the heck does this have to do with pianos John?". Well, if the MOI of the action is high it will feel harder to play. I am not sure if the player could feel this with playing cords slowly at various dynamic levels but it will certainly feel hard to play scales and fast passages. Let's imagine a room full of our cylinders each with a rope attached. Your job is to pull each of these ropes in fast order. It will be a lot easier if they are made of wood rather than steel. But what about balance weight? Use the cylinder again, but this time wrap another rope around the back side and attach a weight. have a shelf for the weight to rest on. Now when you pull the rope you have a weight to lift along with the inertia of the cylinder. The cylinder doesn't move until the weight is lifted. Go back to the room of cylinders. Would you like to have the wood cylinders with a heavy weight attached or the steel ones with lighter weights? One of the things learned from studying MOI is just what Balance weight does. It determines (along with friction and let off resistants) the minimum force to move the action. The total force after that is determined by the force required to accelerated the action minus the force of the BW. At very soft levels of playing the BW will be a significant part of the total force while at forceful levels the balance weight is insignificant. Through the dynamic range of playing the force needed to accelerate the action increases while force to overcome the BW stays the same. Hope this attempt at a non math explanation helps. John Hartman RPT John Hartman Pianos [link redacted at request of site owner - Jul 25, 2015] Rebuilding Steinway and Mason & Hamlin Grand Pianos Since 1979 Piano Technicians Journal Journal Illustrator/Contributing Editor [link redacted at request of site owner - Jul 25, 2015]
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