I agree with everything Michael said above, with these additions...
Strike at 90 deg is the goal, as stated. But, keep in mind, this only happens if you custom bore. A generic bore will have some parts of the scale at 90 deg and some parts not at 90. Further, a generic bore may not have any of the shanks at 90 deg, depending on how the stack elevation was set up relative to the generic bore. So the only real way to achieve the stated goal is to custom bore...but that doesn't always happen in a factory installation. This means the stated goal is often not actually achieved, as the factory adjusts stack elevation to compensate for inevitable inaccuracies in design specification of the action cavity.
Agraffes up to 88, Chickering and Bechstein, does require some rake to achieve clearance to the plate. I have done a Bechstein where I forgot to rake the top half octave, but a little felt removal achieved the clearance.
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Jim Ialeggio
grandpianosolutions.com
Shirley, MA
978 425-9026
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Original Message:
Sent: 03-21-2020 13:45
From: Michiel van Loon
Subject: Grand hammer rake angle
Dear Peter,
A rake angle of 93 to 94 degrees is normal in European pianos. For Renner Germany it is standard. Matthias Stöckle (Renner Germany) prefers 93°. But you can also choose 90°. With Abel it is the same. https://www.abel-pianoparts.de/index.php?index=1&lng=en&menuid=65&ordner=shop-40
I had a discussion with Joachim Leonardy of Jahn about this. He said that it does not matter what you do, as long as the the hammer hits the string in an angle of 90 ° . In the case of 90° your shank has to be parallel with the string. And from that you can deduct the bore length. When the rake angle is 93° the bore length is about 3 mm shorter. You can calculate the bore length.
In some cases the 93° is a way to keep the hammer from hitting the frame or the belly bar. This can happen in the high treble in old Bechstein grands.
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Michiel van Loon
MEPPEL
+31655150644
mvanloon@xs4all.nl
Original Message:
Sent: 03-21-2020 12:53
From: Peter Grey
Subject: Grand hammer rake angle
I have a 1947 Mason & Hamlin Symetrigrand here needing hammers and more. I was surprised to find a rake angle on the factory hammer setup of about 4 degrees acute rather than the customary 90 degrees. I see no APPARENT reason for this such as clearance issues. It does not APPEAR to be a mistake or sloppy hanging. It is consistent throughout. I am seeing significant over-centering in the bass and low/mid tenor which does concern me.
So the question is aside from getting the hammer bore distance correct, is it wise to duplicate this rake angle or change it to the standard? Any comments are appreciated.
Pwg
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Peter Grey
Stratham NH
603-686-2395
pianodoctor57@gmail.com
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