---------------------- multipart/mixed attachment >Richard Brekne wrote: > >Hi Phil and Ron, I wanted to include an illustration with this bit that I= =20 >forgot to paste when I sent it. > >Course there is a difference between the second and third drawings, anyone=20 >care to describe that ? > > > > Phil Ford wrote: > > The position of the jack relative to the hammer shank has no bearing on=20 > the direction of the force being applied at the jack contact point, just= =20 > as the angle of the hammer head and hammer shank have no bearing on the= =20 > direction of travel of the hammer strike point. > > Richard Brekne wrote: > > It certainly does. It is in the end the jack that exerts force on the= =20 > knuckle, and the angle formed between the jack top and the hammer shank= =20 > line is the critical one. I agree that the angle of the jack top relative to the knuckle determines t= he direction of force, but not the angle of the jack top to the hammer shan= k or the jack top to the jack body. Let's say that the jack top is 30 degr= ees from horizontal. The direction of force on the knuckle is 30 degrees f= rom vertical. If you were to move the jack along this force line then the = hammer would move up but the direction of force on the knuckle would not ch= ange, even though the angle of the jack top to the hammer shank centerline = would be changing. Your diagrams 2 and 3 (see attachment) illustrate why t= he position of the jack body does not determine the direction of the force.= The force is being applied normal to the jack top (which would usually me= an a force being applied normal to the top surface of the whippen or rep le= ver). If you keep the top surface of the jack in this same orientation the= n you could move the jack center toward or away from the whippen center (wh= ich would change the angle of the jack top surface to the jack centerline) = and it would not change the magnitude or direction of the force being appli= ed to the knuckle. However, the internal forces on the jack would be different. In diagram 3 = the force on the knuckle is applied as an axial (compression) load on the j= ack. In diagram 2 the force on the knuckle is applied as a combination of = axial load on the jack and shear load on the jack, with the shear load bein= g reacted as a couple between the jack center and the regulating button, wh= ich will cause a bending load on the jack. A jack optimized for diagram 3 = should be lighter than a jack optimized for diagram 2 because there is no b= ending in the diagram 3 configuration. >That the jack remains stable for most of the key stroke relative to the=20 >whippen center line (and is perpendicular to that line) allows you to=20 >disregard the jack and look only at the whippen center line... because=20 >that means the jack top is on that line. But this changes the minute you= =20 >hit the jack tender, or better said.. the second you change the angle of= =20 >the jack relative to the whippen center line. > > > > > >-- >Richard Brekne I agree that things change when the tender hits the button. I thought you = said earlier that we weren't interested in this portion of the stroke becau= se once this happens the hammer is no longer under control of the key. I t= hought we were talking about the portion of the stroke up until letoff. Phil F Phillip Ford Piano Service & Restoration 1777 Yosemite Ave - 215 San Francisco, CA 94124 ---------------------- multipart/mixed attachment A non-text attachment was scrubbed... Name: jack.jpg Type: image/jpeg Size: 10176 bytes Desc: not available Url : https://www.moypiano.com/ptg/pianotech.php/attachments/cc/f3/f6/5a/jack.jpg ---------------------- multipart/mixed attachment--
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