Bechstein hammer bore

[John Delacour]

At 01:14 +0100 16/2/08, Richard Brekne wrote:

>...Be that as it may... let me see if I got this right. Grands only 
>to begin with.... just so that thats out of the way.
>
>String to key bed height minus hammer center to key bed height 
>determines bore length as usual yes ?...

No.  Nothing usual about it.  It could happen.  The bore length is 
determined by the hammer's rest position and the blow.  The hammer 
rests say 2mm clear of the rest cushion and you want say 45mm of blow.

>  then rake is determined by the offset from parallel that the string 
>plane  to the  shank at  string contact for the resulting bore 
>length ?

No. The rake is determined by what is required for the hammer to hit 
the string at the strike line and at a right angle.  The distance 
from hammer centre to centre line of hammer-head moulding is fixed, 
usually at 130mm or 125mm.  On the Bechstein it is probably 130 but 
I'm at home and can't check that.

The string angle in the treble will alter the bore, or perhaps the 
rake, required, but often the lower string height will work in 
compensation.  It depends on the piano.

>The bore length should put the hammer shank at parallel to the key 
>bed at string contact yes ?  So string offset to the shank at 
>contact can be figured from the key bed plane then ?

No again.  If the hammerhead is raked back 2 degrees then the shank 
will exceed the horizontal by 2 degrees.  There is no universal 
requirement for the shank to be parallel to the key bottom at strike 
time and no theoretical advantage in such a configuration.  It 
depends on the piano, the entrance-height etc.  What is right for a 
Steinway A will not be right for a Bechstein B.  What Yamaha may 
teach may be good for Yamahas.  What Steinway specify might be good 
for 5% of Steinways.  Who knows?  The piano has the answer.

It's late and I need to get to bed.  As I say, I intend to write an 
article on all this and also create a web page where people can play 
with numbers and get an exact picture of what happens.  There is far 
too much ignorance about hammer fitting.  A certain design of action 
and keyboard has a certain geometry, certain dimensions, and this 
imposes pretty strict tolerances on the restorer.

JD

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