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Grand hammer rake angle

  • 1.  Grand hammer rake angle

    Registered Piano Technician
    Posted 03-21-2020 12:53
    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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  • 2.  RE: Grand hammer rake angle

    Posted 03-21-2020 13:46

    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
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  • 3.  RE: Grand hammer rake angle

    Member
    Posted 03-21-2020 14:15
    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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  • 4.  RE: Grand hammer rake angle

    Registered Piano Technician
    Posted 03-21-2020 14:37
    Mr. Grey,
    4 degrees acute? That seems to mean that the hammers are tilted towards the proximal end of the shank (away from the belly) and that seems very unusual. It would explain the over centering however. I'm more used to seeing a distal rake (tilted towards the belly) in pianos with string heights too high to make 90 degrees at the shank practical. I'm replacing the hammers on a Schimmel 256 that had a 1.5 degree distal rake from the factory. I decided to keep it with the replacements as without it I'd need a 60 mm bore distance in the bass.

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    Karl Roeder
    Pompano Beach FL
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  • 5.  RE: Grand hammer rake angle

    Registered Piano Technician
    Posted 03-21-2020 17:10


    Okay, so I went back and re-checked my angles (this time carefully with protractor) and I found the following:

     Beginning at note 88...88 degrees gradually increasing to 86.5 degrees at note 31 (lowest tenor note). Then top of bass is at 86 degrees tapering back to 88 degrees at note #1.

    So in fact it's not as consist​ent as I initially thought. I now see no reason that I cannot correct it, though I'm thinking I might keep the whole thing at 88 degrees or perhaps 89 degrees. I've already determined that the strike point needs significant adjustment at the note 72 area (almost 1/8"). Fixing this should bring the mounting point closer to the knuckle which should in turn reduce touch weight a tad which might allow me to remove some lead from the keys. That would be nice.

    I'm thinking that the situation might have arisen due to a tail guide going awry and not being noticed during install...just a theory.

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 6.  RE: Grand hammer rake angle

    Member
    Posted 03-21-2020 18:20
    reading what the job presents can be like playing a game of telephone...attributing mistakes, poor attention to detail, as well as purposeful work all the same credibility, and never having the slightest idea what was actually intended, before guessing why they might have intended it.  I just think the problem through for myself, and proceed from that perspective. That way, I know whose bright idea is actually at fault or sometimes, surprise surprise, who pulled off the enlightened design.

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    Jim Ialeggio
    grandpianosolutions.com
    Shirley, MA
    978 425-9026
    ------------------------------