Richard and list, Earlier I wrote; > Bill Ballard touched on the influence of the jack/roller relationship > to the line-of-centres in his recent post. His was an excellent > point. The location of the jack/roller contact for many actions, is > very poorly laid out. Richard Brekne responded; >Yet there are seemingly two somewhat opposing friction concerns here... the >roller sliding on the repetition lever... vs the rollers contact >situation with >the jack. I agree Bills point was a good one in as much as it addressed the >unobtainability of this line of centers / knuckle consideration. 'Line of centers/knuckle optimisation' is obtainable. We have done it with our action (see my earlier post). The problem with conventional actions is that it is unobtainable when the wippen flange center to jack center distance is 99 mm and the roller slot to hammer center is only 17 mm. Why do manufacturers stick with this 99 mm figure? It seems that because Iserman used it and Steinway used it historically, most of the piano design world has gone into some kind of design paralysis, on the strength of a couple of manufacturers adopting a questionable layout. The 'opposing' friction concerns to which Richard referred relate to two separate levers and their relationship to the roller, it is possible to design an action which deals with both matters separately in the one design. Jack/roller relationship to the line-of-centers During that part of the keystroke between rest and the contact of the jack heel/tender with the let off button, the wippen (with the repetition lever and the jack) acts as a single lever, ie. there is only contact of the wippen with the capstan, wippen flange center (fulcrum) and the roller. The arc relationship of the jack with the roller at this time is controlled by; 1) The jack slot to hammer center distance 2) The jack center to wippen flange center distance 3) The diameter (or more correctly - height) of the roller 4) The hammer boring distance (or more correctly - the arc of travel of the hammer shank during the execution of the key stroke) Adjustment of any of the above parameters will change the jack/roller contact position with respect to the line of centers. All four of these parameter are standardised in the Overs action to minimise friction. Repetition lever relationship to the line-of-centers The repetition lever is, by and large, taken along for the ride during the execution of a key stroke up the point where the hammer is caught in check (while the repetition lever will have made contact with the drop screw - it is irrelevant to the parameters presently under discussion, since at the point of hammer check it is no longer in contact with the drop screw). At this point the repetition lever depression will be determined by the height of hammer in check. Therefore, before considering where to position the repetition lever center, the designer must first decided on a check height. I chose 12 mm from the string as the height for the hammer check. I then set the repetition lever center height to intersect a line which passed from the hammer center and through the repetition lever/roller contact. This allows the repetition lever/roller relationship to be optimised at the moment the repetition lever pushes up (or holds up - during dynamic performance) the hammer as it rises out of check. In an earlier post I wrote; >. . the > jack/roller contact position is of equal importance [to that of the >capstan/wippen heel] Richard replied; >This is another point discussed a bit lately... and none of those >who seem active >in action design parameters who have written about this lately have >seemed to see >the importance of this.. But how can they fail to see? Just watch a standard roller on any Kawai, Renner, Yamaha or Steinway action model as it leaves the key rest position. The roller swings back as it rises - friction friction everywhere. >I frankly do not see how this ends up being an important >point . . I would love to hear some explanation Check out Terry Farrell's post. He's onto it. Regards, Ron Overs -- _________________________ Website: http://www.overspianos.com.au Email: ron@overspianos.com.au _________________________
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