William, A few thoughts if I may, since the basic specs in the Boston action are the same as the Kawai: - Dip of .400 is pretty much the same as normal 10.2mm spec, so thats fine. - Blow of 46mm is normal - Key balance hole is probably too loose, allowing the key (and its lead weights) to bounce up off the balance rail. This bounce can coincide nicely with the return of the hammer, sending it back up with more energy than the hammer alone. To test this, place a finger firmly on the key button just behind the balance pin and do the Staccato blow. If this reduces the hammer bounce, you have a solution. Make the balance hole tighter, so that is will SLOWLY drop back to rest position instead of freely falling. - Balance rail bedding keyframe should be rechecked as well - Hammer rest felt should be about ½ the hammer shank thickness, so you may have it correct already. - Hard back rail cloth could contribute. - Very loose hammer centers might contribute as well, but I wouldnt consider that the prime cause. As Ron said, if one tries to make an action do this, one can usually make it happen. But it really shouldnt show up when playing music. Check the balance rail holes thats my best guess as to the primary problem, and set the hammer line a little lower along with resetting the hammer rest (rebound) rail to match. Don Mannino From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of William Monroe Sent: Thursday, July 29, 2010 6:20 PM To: pianotech at ptg.org Subject: [pianotech] Bouncing Bostons Hi List, Anyone know of anything chronic in Boston Grands (GP178) that has the hammer double striking on a quick/firm staccato blow? I've got one that does. Anyone have any ideas/solutions? The piano is finely regulated otherwise (just today, in fact). 1 3/4" blow, about .400" Key Travel, Checking about 1/2", Rep springs are definitely NOT jumpy. In all other ways, the action plays nicely, controllably. And that is no mean feat. I took some DW/UW measures today out of curiousity, and they were haywire. DW range from 62g - 46g, UW from 18g to 35g or so. My thoughts are turning to action pinning (haven't checked yet). Key Bushings and pins are clean and lubed (teflon), but that's as far as we got. Wondering if tight pinning (of any parts) might contribute to this rebounding back into the strings - and it is a full rebound. You can watch the hammer appear to bounce off the rest rail, though I'm not convinced that is exactly what is happening. Kind of musing aloud here.............. William R. Monroe -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100730/777f25d0/attachment.htm>
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