[pianotech] Hammer rake angle

[Gregor _]

Jurgen,

the Renner order form for new hammers has as standard 87.5 degree (or 2.5 degree in your nomenclatur).

I must admit that I didn´t hang in new hammers for more than 15 years, but I remember this: the hammer should strike the string at 90 degrees. To do so the bore angle has to be different from 90 degree. In that case the hammer shank is not parallel to the string when the hammer strikes the string, which assures that the shank falls back just due to gravitation. Another way to check the correct angle (or better: geometry) is to measure the "Stielschräge" (don´t know the English word, but I know you speak German). Bring the hammer to the string and measure the distance from the upper end of the shank to the string and measure the distance from the lower end to the string. The difference between these 2 measures should be the thickness of the hammer shank, usually 6 mm (or 5.6 mm). 

Depending of the geometry of the whole action it might be that a piano has a correct Stielschräge (6 mm) only then when the bore angle seems to be too much like your Heintzmann.

Gregor

------------------------------------------
piano technician - tuner - dealer
Münster, Germany
www.weldert.de




To: pianotech at ptg.org
From: pianoforte at pianofortesupply.com
Date: Thu, 20 Aug 2009 18:35:05 -0700
Subject: [pianotech] Hammer rake angle








What is the consensus on a proper rake angle for boring and hanging upright hammers?



I am working on a ca 1910 54" tall Heintzman piano, it is a really fine instrument, complete with a full sostenuto.  The original hammer rake angle is a full five degrees throughout.  It looks quite extreme, yet I am reluctant to change it without a good reason on the new hammers I will hang.  Is there a good reason to change it to a more "normal" 2 degrees?



Why is it that most upright hammers do not strike the strings at 90 degrees  like most grands?



Jurgen Goering
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