I was thingking in terms of hammer bore distance Dale One mm change in the agraffe height probably doesn’t make enough difference to worry about trying to factor it into your bridge height calculations. If I had more energy I’d do the math but trig takes me some time these days to get the brain cells fired up. Anyone? David Love www.davidlovepianos.com Good Thoughts Jude I was just checking the height of a new 1/4 inch German aggraffe against the height of the one in the 70's Stwy D I posted about. I've not confirmed this yet but it appear that the holes on the new part will sit about 1 mm lower when installed. I'm going to pull one old one out & install it side by side. If this is true then we need to take this in to account when rebuilding/ establishing a string plane. In this case, 1 mm would help smooth things out a bit. I too thought why not machine the plate a small amount to lower the elevations. Any body have any thought about that? The curving string plane onStwy/other plates is so prevalent & reliable that it must be intentional... Hmm Reminds me of a Ron-ism,,, " A Factory screw up we can sell as a feature"? or some such. Close enough Ron? Dale In the case of these particularly nasty string height sections, what are our options? Although somewhat unsightly, what about adding washers or dre ssing the bottom of the agraffes' base? Do you feel it necessary to tighten the agraffes down. When is too tight? Any torque specifications. One idea I've been messing with is not going so tight and using a bit of thread lock. As I understand the strength of threaded bolts, full strength is reached before a bolt is fully cinched down anyway. I'll try to get some torque measurements of what I mean. Comments appreciated... Jude Reveley, RPT Absolute Piano Restoration, LLC Lowell, Massachusetts (978) 323-4545 ----- Original Message ----- From: erwinspiano at aol.com To: pianotech at ptg.org Sent: Tuesday, March 24, 2009 9:29 PM Subject: Re: [pianotech] Increasing bridge height =0 D 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 stringA 0heights 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 changing=2 0the 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=2 0to 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:=2 0Tuesday, 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.davidlo vepianos.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 Live traffic, local info, maps, directions and more with the NEW MapQuest Toolbar. Get it now! Live traffic, local info, maps, directions and more with the NEW MapQuest Toolbar. Get it now! -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech_ptg.org/attachments/20090325/8d48f41b/attachment-0001.html>
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