Richard, Sy, Frank, Richard and list, Regarding my recent posting on the Kawai KG jack design. All of the earlier KGs with wooden jacks, from the No. 500, 600 and 650 etc, through KG to KG#C are of the same basic design, ie. they have a 6.5mm upturned jack tail with a tail-contact-arc-radius of 4.5mm. It is the combination of the degree of vertical offset with the large arc radius, which leads to the higher than average friction figures (and wear rate). Check that test I described previously, with wippens from other makers (I see Richard Moody's into it). The phenomena is not confined to Kawai alone. Several others, including the modern Hamburg Steinway and Yamaha wippens, wear the let-off button cloth in a similar fashion (but to a lesser degree). Richard Brekne asked whether there were any neat fixes. Well yes, I believe there are. I have been working on this, and other action geometry matters, since January this year. I have a discovered a design formula (which may not be new, but its new to me) for calculating the optimal design of a jack tail. 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. 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. Unfortunately, I cannot release details of our design at this time. However, we expect to have the new action ready for release at the Australasian Piano Technicians convention in Sydney, July 6-9, 2000. We plan to make this action available for both OEM and retrofit markets. I have a circa 1977 Steinway D (pictured on the home page of our web site), which we rebuilt in 1996, with a standard action and custom Imadagawa hammers. We are planning to treat this piano to little 'shock of the newą, installing one of our new actions. Not from the hallowed halls of the original manufacturer? Ah well, its a convenient way to get rid of the split original action rails. Thank you all, for a continually interesting list. Ron E. Overs Sydney, Australia Email: ron@overspianos.com.au Website: www.overspianos.com.au
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