Gregor, It seems to me it would also depend on other aspects of the action geometry, especially the shank length which would have an impact on how quickly the angle and strike point changes in response to wear on the hammer. I have always assumed that a 90 degree angle at impact was the ideal, but that doesn’t take wear and subsequent lessening of the angle into account. Maybe the best compromise would be to bore so that the angle at hammer 88 (where the strike point is the most critical and the wear is minimal) is at 90 degrees and taper it down in stages so that the tenor and bass hammers are at slightly more than 90. As the hammers wear down, they at least pass through the ideal strike angle and don’t overcenter excessively when worn. I haven’t bored any hammers in some years, so I haven’t tried this out, and even if it’s valid it may not be worth the extra work. Other thoughts? Kerry Kean www.ohiopianotuner.com <http://www.ohiopianotuner.com/> _____ From: Gregor _ [mailto:karlkaputt at hotmail.com] Sent: Wednesday, May 20, 2009 6:56 AM To: pianotech at ptg.org Subject: Re: [pianotech] Upright Action Geometry Floyd, I am not shure if I understand your question correctly. The first that comes into my mind: measured from which point? I guess you are asking for something that refers to what we call in German "Stielschräge". I.e.: bring the hammer to the string and measure the distance from the upper point of the shank to the string and measure the distance of the lower point of the shank to the string. The difference between these two measures should be the thickness of the shank, usually 6 mm. This Stielschräge depends on the hammer bore angle and the position of the shank in the hammerbutt. Gregor > From: fg at floydgadd.com > To: pianotech at ptg.org > Date: Mon, 18 May 2009 10:05:52 -0500 > Subject: [pianotech] Upright Action Geometry > > List, > > I'm assembling an vertical action model as described in the Journal several > months ago. I neglected to take one measurement when I was disassembling > the piano from which I got my parts. What should be the angle relationship > between the hammershank and the string plane when the hammer is in its > striking position? I've found an article by Jack Krefting in the '82 > Journal that states that in a grand the two should be parallel. Is this > also true for the vertical action? Does having the answer to this question > represent a method for establishing bore distance in an action where the > hammers are so badly worn that the original bore distance is uncertain? > > Floyd Gadd > Manitoba Chapter > _____ check out the rest of the Windows Live™. More than mail–Windows Live™ goes way beyond your inbox. More than <http://www.microsoft.com/windows/windowslive/> messages -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20090520/ac8dae70/attachment.htm>
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