---------- > From: Ron Overs <sec@overspianos.com.au> > To: pianotech@ptg.org > Subject: Re: Kawai let-off (poor jack design?) > Date: Thursday, May 06, 1999 8:56 AM >. Check out the additional down weight required to push a typical modern action jack through >let-off (ie. a jack with a smoothed and slip coated tail and roller contact surface); it will >typically require 150 grams. Prototypes of my new jack, which we recently manufactured >(installing them into a rebuilt Kawai KG6), required a down weight of 125 grams to execute >the >let-off. I have always been interested in the additional weight needed to push the jack through let-off. You say it will require ADDITIONAL 150 grams.?? Perhaps you mean milligrams? Centegrams? 15 grams?? The problems I have had is the momentum of the 54 gram weight carrying the key though letoff or only to letoff when placed on the key at rest. So a "feel" of the friction of let-off (rather than weight measurement) has always guided me in evualtion of touch in that area. Not too scientific, but at least the player and I can focus on that if necessary through sensation of finger pressure. (I was taught the distance of after touch determined the feel of "touch" if the down weight was with in range, and that is different according to player preference) > Our new jack design is part of an overall redesign of the grand piano action. Recent >prototypes, with the down weight set at 54 grams, have yielded up weights in excess of 40 >grams. If this translates to real world factory piano actions, friction figures of less than 9 >grams look to be achievable. I have recently wondered why factories have never published "optimal upweights" That should indicate "friction". Carrying it out further I am wondering why there are not up and down weights given for dampers at rest and then for dampers raised. Ric Wondereder
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