Bechstein hammer bore

[Richard Brekne]

Hi JD  Comments below

But before reading, I'd like to try your basic approach to determining 
the hammer bore and the rake angle. There are a few problems down the 
middle of the scale with agraffes at significantly different heights... 
but I have no opportunity to alter that situation so I'll have to make 
the best of it as it is. So by all means supply a detailed approach and 
I will give it a whirl.  The below then is just for discussion in general.

         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 ?...

    JD:

    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.

I beg to differ with you here. While it is true we can find different 
perspectives for doing this that end up with similar results... using 
the string to key bed distance minus the hammer shank to center distance 
is with out a doubt thee most usual way to find the bore length I've run 
into these past 30 or so years.  This archive is full of references to 
that and there are several articles written in the journal along those 
lines.  None of that means that this is the only and best way to do 
things... of course...

        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.

Thats in theory... in practice you don't find them like this.  Measuring 
factory hammer sets you see its always more along the lines of give or 
take a couple mm. Even robot factories like Yamaha end up with those 
kind of variances. I've seen three sets of pre glued factory sets with 
both variant strike lines, variant rake angles, variant center pin to 
center mold distances even variants in where the hole is centered.  Two 
of these sets were for the same piano ordered a few years apart from 
each other. In all cases none of them really matched the existing set. 
Thats why I do my own.

    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.

There are three planes one ideally (tho its impossible at the outset) 
wants to get all parallel with the perpendicular hammer. The string 
plane, the shank plane at contact, and the keybed.  Since the keybed and 
string plane are nearly never parallel one is forced to select two of 
the three.  So far, most of what I have seen written leads me to believe 
that its pretty much hip or hop as to whether one decides to have the 
shank parallel with the keybed or the shank parallel with the strings 
with the hammer at string contact and perpendicular to the shank.

I am aware that there are those who argue that the hammer needs to be 
perpendicular to the string-planes at contact... and of those who take 
this view their is difference of opinion as to whether or not the shank 
need be perpendicular to the hammer as well.. or if it should be 
perpendicular to the keybed.  One way or another... the degree of 
variance between the string plane and the key bed builds in a degree of 
energy loss... if the various argumentations about the need in general 
for a 90 degree orientation of the hammer at impact holds for any.  
Which one is in the end most important to match... I cant say I can 
show.  One just reads the various opinions out there and makes ones best 
call.

         >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.

Yes, well as I said... I would very much like to try your approach.  Its 
always cool to try things a different way then one is used to.  So if 
you can manage it within the next week or so... put up a basic 
description of your approach.  I'm sure there are several who are 
interested. 


    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

I'm off to New York for a week for a visit to the S&S factory and the 
city in general so I wont be able to follow the list easily.  If you do 
post your procedure, please send it to my private email adress as well 
if you would be so kind.

Cheers
RicB