At 10:46 PM +0200 10/22/00, Richard Brekne wrote: >Bill Ballard wrote: > > > And speaking of "ya ever look close there", did you ever watch a jack > > get momentarily pulled backwards (squashing the jack button felt) > > which the cycle first starts up? > >Yepp.. noticed this right away dinking around with the spread on my >action model. >Also notice that when the spread is just barely on the wide side >(jack center on >the perpendicular to hammershank at the knuckle with the hammer at rest) this >didnt happen. That seemed to be because the jack looked more like it >was behaving >like a pivot during this portion of the keystroke. Instead of being dragged by >the knuckle,,, it rocked nicely on the knuckle while both pieces were moving >through their respective arcs. It is ever so momentary. I've always assumed that the sliding friction between the top of the jack and the knuckle had a static phase, one which at the start locked the jack top to the knuckle, and which was not transformed into a sliding friction until the point where the potential energy store in the compression of the jack adjusting button felt finally exceeded the force of static friction at this spot. Remember that while the contact point on both arcs (the knuckle's and the jack top's) are both heading in the same direction, the horizontal component (sliding motion) is greater in the knuckle's arc, and it is also increasing. No wonder the jack is not inclined (no pun intended) to immediately break free of this static friction grip with the knuckle. I'm not sure that this is the explanation for the effect, or whether your observation regarding the spread contains the answer. It would seem quite likely that this effect could still occur even in an action in which axes and contact points had been properly dealt with, such as in Ron's action. How modest of Ron not to respond when I asked if he had anything to tell us about his action. Seriously! He'd given a full description of it in a thread I'd missed last month. Bill Ballard RPT NH Chapter PTG "No one builds the *perfect* piano, you can only remove the obstacles to that perfection during the building." ...........LaRoy Edwards, Yamaha International Corp
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