Before the discussion goes completely off-topic I'll give my take on
the question of the strike line.
My definition of the strike line is the first (straight) line that is
made on the drawing board in the designing of a piano and is the line
that crosses the strings at the point where the hammers are
_intended_ to strike the string, with the hammer-heads at a right
angle to the strings.
From this line, the line of the string to the top bridge (agraffe
etc) and the line to the first bridge pin are drawn in a certain
proportion one to the other, this proportion having been determined
by the piano maker, through his own experience and that of his
predecessors and masters, to be the very best proportion for the
piano in question and similar pianos.
In a piano of reputable manufacture it is unlikely that the choice of
these proportions is anything but the best, and no matter what the
condition of the soundboard is, it is unlikely that the tone of the
piano can be improved by striking the string at any other proportion
of its length than that set by the maker.
A bird's eye view of the strike line will show it as straight. Gross
errors in the placement of the agraffes and the bridges will
frustrate the designer's plans. Lesser errors will make very little
difference except in the extreme treble.
A view of the strike line from the front (ie. a line joining the
points that represent the strike height at the strike line) will
occasionally be straight but more often than not it will have steps
(at the breaks), slopes and curves. In addition to this,
particularly on pianos with agraffes all the way up, the angle of the
strings to the horizontal (going at an upward slope to the bridge)
will increase in the top section towards the top. This also needs to
be taken into account.
If the hammers are correctly bored as regards bore length and bore
angle, by taking into account the above factors and calculating the
bore given a straight hammer rail at a constant height above the
key-bottom (and this must be most carefully verified and adjusted as
necessary having regard to the total geometry of the action, which is
a whole nother story) then each hammer will strike its string at a
right angle and at the strike line, and the best possible performance
will be had from the instrument.
If I buy standard bore hammers for a Steinway my chances of getting
things wrong are roughly 100%. I worked on a very fine 1970s Hamburg
model B a couple of months ago that had the original hammers and
these had been certainly been refaced once or twice but this would
have accounted for the removal of say 3mm from the nose of the hammer
at the maximum. It was obviously a great piano but performers were
complaining of weaknesses. I had Abel make me a set of raw hammers
and bored them according to my calculations from the careful
measurements I had taken. The bore of my hammers differed from the
originals by up to 8 millimetres! and, since they were, for the first
time ever, hitting the strings in the right place at the right angle,
the piano has a purity and power that it never had before.
One of my current jobs is a 1927 Model O. If I had ordered standard
bore hammers with a bore length of 45 mm, again I would be wrong. At
places in the scale I need a bore length of 49 mm because the string
heights are not what they should be for the given action and 45mm
hammers.
The alternative to doing things properly is to take no measurements,
make no calculations, buy standard hammers and make the best of a bad
job by shifting things backwards and forwards until they sound OK.
JD
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