This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Berhard, Don, Sarah, Would a somewhat flexible support on the pivot side help in absorbing some oscillation ? I’ve seen strange results when the underside of the hammer flange is cut in an arch shape (the shape of Steinway flange). The first idea was that it helps decoupling between hammer/shank and the rest of the action, so the system being more free, more energy is transmitted. Easy experiment and immediate result – unfortunately, one can’t tighten the flange screw with enough force (and without changing the pivot position . I like also to understand what is the role of shank flexion in tone dynamic (or expressiveness) seem to me that the shanks are flexing easily with the hammer acceleration, I don’t see them like a very rigid support. When checking for rubbing hammer tails, most shanks are flexing a little without so much pressure on the head. Indeed lighter hammers seem to be more responsive to acceleration, but may be harder to control, too much “free energy” as you said Berhard, vs a heavier hammer (or one that is glued farther on the shank ?) that send a lot of feedback to the pianist thru action compression, then work more slowly for tone production (may be giving more the impression of control, up to some point nowadays) But may be that is a totally different subject in the end … Best regards. Isaac OLEG -----Message d'origine----- De : pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]De la part de Bernhard Stopper Envoyé : vendredi 19 décembre 2003 01:02 À : Pianotech Objet : Re: Cockeyed hammers / Don Gilmore Don/Sarah, To design a hammer so that its pivot coincides with the center of percussion is THE way to get a free sound and the maximum of energy transfer to the string. it also allows the hammer to reject the fastest way possible because oscillations in the pivot produce friction and slow down hammer movement at contact point. i did several simulations with software called pro/mechanica and reshaped hammers after results found. one could say that actual hammer with heavy felts have their center of percussion much far away from the pivot than lighter hammers have. putting a small lead in the tail of the hammer can make them come closer to that point. center of hammer mass should ly on a line along the center of the hammer shank and the center of percussion is at distance x from pivot that can be calulated by the formula x=I/(m*y) with I= moment of inertia, m=mass, y=distance to center of mass regards, Bernhard ----- Original Message ----- From: Don A. Gilmore <mailto:eromlignod@kc.rr.com> To: Pianotech <mailto:pianotech@ptg.org> Sent: Friday, December 19, 2003 12:22 AM Subject: Re: Cockeyed hammers / Don Gilmore Well, I didn't mean to imply that the impulse at the pivot is all absorbed; but it is all lost as far as the string is concerned. The center of percussion is one of those counter-intuitive phenomena in dynamics. For the multitude of college students that only take a semester or two of physics, the concept of forces on a free body acting at the center of gravity is a paradigm that is hard to dislodge. For an object in free space or translating in a straight line, which comprises most situations, the center of gravity is always used. But for an object pivoted at some location other than its c.g., all bets are off. The most publicized version of this is a baseball bat's "sweet spot" as you described. Think of a wooden board hung from a pivot point at its top. If you strike the board up near the hinge, the pin will experience a force coming from the direction of the strike. But if you strike the board at the bottom, the pin will experience a force in the opposite direction as the board tries to spin about its center. There is a point in between these two where the pin force is neither positive nor negative and the pin will actually see no force. This is the center of percussion and is not located at the centroid of the board. It's not usually even particularly close. It would seem to be a good idea to design the hammer so that the string contact point of the head passes through the center of percussion. That way the maximum amount of energy would be transmitted to the string...like dropping a ball on it. But I'm not sure if they actually design them that way. Don A. Gilmore Mechanical Engineer Kansas City ----- Original Message ----- From: Sarah Fox <mailto:sarah@gendernet.org> To: Pianotech <mailto:pianotech@ptg.org> Sent: Thursday, December 18, 2003 2:38 AM Subject: Cockeyed hammers / Don Gilmore Probably any baseball player would know that it's not smart to hit the ball with the very tip of the bat. It makes for a nasty shock to the hands (and to the extent that the hands are not rigid in space, it takes away from the power transferred to the ball). Why do they do this with piano hammers? More to the point, is this not considered an unneccessary demand to put on the hammer flanges and bushings? Perhaps it's also a drain on efficiency? Wouldn't it make sense to have some sort of asymmetrical molding whose center of mass is on the far side of the action center, so as to put the center of mass of the hammer assembly closer to the line of strike? Also, wouldn't it at least make sense to angle the head of the hammer inwards slightly, so that the radius to the head's center of mass is perpendicular to the strike axis of the head? It seems to me that this would help to control wobble in the hammer I'm not sure I agree about part of the impact being "absorbed" by the pivot. Sure, there would be force against the pivot, but for impact to be absorbed, the pivot would need to be compliant and inelastic. I realize that's true to an extent, as no system is ideal. However, do you think this would be a substantial drain of energy? It seems to me that the hammer felt and the strings are far more compliant and are closer to the center of mass, such that almost all of the energy would be dissipated there (rather than at the comparatively rigid center). Have you ever measured this? Just curious on your take. I can't do much more than scratch my head about this one. If the hammer were perfectly rigid and the center bullet proof and noncompliant, there'd be nothing to worry about. But considering that it does the hokey pokey and shimmies all about... Well, I don't know. Peace, Sarah ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/3d/f6/94/99/attachment.htm ---------------------- multipart/alternative attachment--
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