I would venture to say that in most verticals, the shank is not quite
parallel to the string point when the hammer strikes the string. It's shy
by approximately 5 degrees, which I'm sure varies from piano to piano.
The following is from "Piano Tone Building," edited by Del Fandrich.
It's from a 1919 convention of piano techs, manufacturers, et al., when they
are discussing the possible standardization of action brackets. Over 200
different kinds were in use at the time. Brackets are mine, added to
clarify things that might not be so clear.
F.H. Abendschein [of Staib-Abendschein Co.]: ". . . The three most
important centers of the action are the butt, wipp[en] and fly [jack]. The
distance between the butt and wipp [center pins] is 3 1/4"; that covers at
least twenty-five actions of different makes and ages. It has always been 3
1/4" in well-built actions. This drawing shows that the wipp [wippen center
pin] is 1/2" nearer the strings than the butt center. The velocity diagram
automatically works out that distance. When the action is set so that the
wipp center is 1/4" to the rear of the butt center, this permits the front
of the action rail to assume an angle of 97 degrees. This insures a maximum
efficiency of the action movement. With this setting, the face of the butt
flange stands at an angle of 90 degrees. All these angles are reckoned from
the bed [keybed], which is assumed to be horizontal. The blow distance of 1
7/8" seems to be adopted by all manufactureres -- the correct distance is
2", but an allowance of 1/8" is made for the wear of the face of the hammer.
The distance between the butt center and striking point should be 5 5/8".
This has been used in grands right along, but no manufacturer has ever given
a reason for that. The distance between the butt center and steel strings
should be approximately 2 1/8". If you set an action with those
measurements, you will always get it right, regardless of length of shank,
providing the boring of the hammer is 2 1/2" in the treble, from center of
shank boring to the face of the hammer. Like many other things, many piano
makers do this not knowing why.
The front of the rail assuming an angle of 97 degrees when the butt
center is 2 1/8" from the string, the wipp center is 1/4" closer to the
string than butt center. The position of the action rail lug, the hammer
rest and spring rail rest should be standardized. Assuming that we did
standardize these three points, they would be of no avail unless the action
is set 2 1/8" from the string. If the butt center is 3" from the steel
string and we still have a blow of 1 7/8", the contact point on the butt is
higher than when set at the proper distance. You must raise your hammer
rail to meet your shank -- more blow felt is required under the hammer rail
and a loss of power ensues. Many houses use the same bracket but
continually get different thicknesses of felt under the hammer rail, because
they don't get the proper distance from the butt center to the string --
setting the action as they do from the front of the case. If they were to
gauge their cases when received, the distance from the front of case to a
line dropped perpendicular from the striking point -- they could always set
their actions the same."
From here they continue talking about standardized action brackets, but
the distances of wippen and hammer center pins from the strings mentioned
here might help with your question.
Some supply houses, when furnishing new hammers from old samples,
determine the original length of the hammer by just adding 1/8" to the
highest treble hammer.
It seems I was reading something else recently, regarding this very
question -- determining hammer length, or bore distance for a vertical
action -- but I can't remember what it was. Perhaps an article on vertical
hammer replacement in the Journal.
Mr. Abendschein says above that the butt flange center pin should be
about 2 1/8". The center of the shank in most butts is just behind the
butt center pin by about 1/8", i.e., farther from the strings by about 1/8".
If the shank were held vertical, this would make the bore distance (center
of shank to tip of hammer) also 2 1/8". But most vertical hammers have a
bore distance of at least 2 1/4", if not more commonly 2 3/8" to 2 1/2".
This would make the shank sit back toward the front of the piano when the
hammer is in contact with the string.
So, no, I'd say that in most pianos, the shank is not vertical when in
contact with the string. To determine bore distance when the originals are
so worn, I would a) see if shims have been added under the original hammer
rail rest pads, b) look at hammers #1 and #88 to try to see what the
original profiles of the hammers were and how much felt has been removed if
they've been filed and reshaped, c) regulate one note with what was, to the
best of your knowledge, the original key height, blow distance, dip, let-off
and checking distance to see how the aftertouch comes out, i.e., how far the
jack clears the butt leather, and whether the capstans have to be turned
ridiculously far out or into the keys, and you'll probably come very close
to what the original bore distance was.
I know this has been lengthy and round-about. There's probably a more
concise article somewhere, but I can't find it just now.
--David Nereson, RPT
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