The numbers are neither arbitrary nor selected just to make a data sheet work. If you were to design an action from scratch, you have to start somewhere and design regulation specs that seem arbitrary from the outside, turn out to be interdependent. If the piano is already built, one would build the action from the top down; that is, certain criteria are already inferred such as entrance height, casepart dimensions, string heights and strike ratios that will ultimately determine the key height, stack location, certain lever arm dimensions, bore distance etc. The final determinations would be key proportion and rail heights. This makes what we encounter when we're restoring an existing action quite counterintuitive, where we're given a start and an end, but have to make sense of the middle and still conform to normal regulation specification ranges. If you look closer at my example, I didn't change the blow distance at all and it remains at 46mm. I used the full overall travel of the hammer along its arc relative to the keydip without interference from let-off or the string. If anything, aftertouch is the most flexible if you acknowledge that is ultimately the by-product of the entire action design set-up. Also defining aftertouch as the moment the tender hits the jack is different than defining it as the bump you feel in the key, which explains the difference between 2.6mm and 1.5mm versus say 1mm. To try to force an action to have 46mm blow and 1mm aftertouch when you already have defined specs for string heights, lever arms, stack location, key proportions, take your pick, just won't work. Gotta go tuning but I hope I clarified more than confused. Good luck. Best, Jude Reveley, RPT Absolute Piano Restoration, LLC www.absolute-piano.com ----- Original Message ----- From: David Love To: pianotech at ptg.org Sent: Thursday, January 07, 2010 12:05 AM Subject: Re: [pianotech] Action Ratios OK, I get it but what bothers me is that the "choice" of defining the aftertouch is just that, a choice in order to make the numbers work. It's a bit too loosely defined to my liking. With Nick's side of the equation 44 mm makes sense because, in fact, 46 mm blow - 2 mm let-off is about how we set it. But where does 2.6 mm aftertouch come from. It appears as if it's an arbitrary number that must be assigned to an overall key travel of 10.5 mm in order to make the w/s ratio conform to the effort/resistance ratio. Similarly on yours, the 1.5 mm makes more sense, I suppose (though it's really more like .75 mm in practice if we use the blow, let-off numbers as a reality check) but then your blow distance is artificial in that it must deviate from the actual blow distance in order to make your w/s ratio conform to the effort resistance ratio. So what does the w/s then really tell us? That we can play with the numbers to make things work but it doesn't apparently have any real world application. It's arbitrary. So the question still stands as far as I'm concerned. Suppose we want 10 mm dip, 46 blow distance where do we set the effort/resistance ratio and who can we calculate that (if we can)? Or do we resign ourselves to "experience has shown." David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100107/79288618/attachment.htm>
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