Hi Dave Yes, unless I'm missing something, it remains the same. If the string plane is raised 2 to 4 mm or so by elevating the bridge height and the corresponding bore distance changed...so what? To ideally maintain the same action ratio & bore distance in these cases is to calculate a graduating bore distance so that, in reality, when the strike point of each hammer touches the string the shanks all travel to the same plane before returning to rest. Imagine for a moment if all hammer were held against the strings at the same time the shanks would form a straight line if the correct bore is accomplished We recently found string heights in the agraffe section of a 1971 Stwy D of 193 mm at note 21 & 196 mm at the last aggraffe. This could lead to a huge boring mistake if standard bore hammers are used or the hammers were bored to only one string height dimension. In such a case Octave four which always gets the most use is already over centering significantly from the very first day contributing to a change in action ratio & regulation. The bass 201 mm to 203 I highly recommended string height measurement for each and every hammer job. Subtract the center pin height & the bore distance is known. Simple tools... simple formulas..elegant outcome. Regards Dale But isn’t that what we’re talking about? Raising the plate height and thereby the string height and then changing20the bore distance to accommodate that change. Does the action ration change then? I can see where if you simply changed the bore distance and left everything else alone but in this case doesn’t the leverage remain the same? David Love www.davidlovepianos.com To the best of my knowledge, changing the bore distance changes the shank upper lever arm and thus the hammer shank ratio. This changes the movement at the knuckle, the lift at the capstan and the key leverage. Unfortunately and most unconveniently for the sake of simple trig, the shank angle at rest is only equivalent to the shank upper lever arm when the bore distance is equal to the blow distance. Humbly submitted, Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545 ----- Original Message ----- From: David Love To: pianotech at ptg.org Sent: Tuesday, March 24, 2009 2:24 PM Subject: Re: [pianotech] Increasing bridge height It does? How. If you raise the string plane and increase the bore distance accordingly so that the shank angle at rest is the same as it was before, how does the leverage change? David Love www.davidlovepianos.com Of course, changing the bore distance does affect the entire action leverage... Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090324/af85ba1d/attachment.html>
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