At 15:04 24.08.95, DAVander@aol.com wrote:
|: ...rebuild a Steinway upright piano, circa 1902....
|: The work to be done includes shimming the soundboard, a
|: new bass bridge, new strings and tuning pins, new hammers
|: and hammer butts, reconditioning the wippens, keybushings
|: and keybed felts, and tuning and regulating.
|: ...changing a scale design. I desire to correspond with
|: someone who has experience in scale design to walk me
|: through the measurements and calculations necessary.
There is almost certainly no point in rescaling the plain
wire section of this piano since if the bridge line is wrong
(which it is not in this case!) there is nothing you can do
short of fitting another bridge. Some pianos, mainly
German, can be given a more singing and sustained tone by
reducing the tension overall but this is not necessary on a
Steinway which generally has string tensions in the mid
treble of 150-160 lbs. except at the extremities. At the
bass end of the long bridge you can expect to find a tailing
off of tension towards the break perhaps to as low as 120
lbs. This is to avoid stiffness in the strings and
consequent bad harmonics as the bridge runs out of space. A
more gradual tailing off of tension is to be expected at the
top of the treble for a different reason, namely to ensure
that the strings remain within the tensile limit of the
wire. On note 88 (of almost any good piano) you would
expect to find a speaking length of 48mm. and a #13 wire.
To calculate the tension, multiply the frequency in cps.
(4186.01) by the length in cm. (4.8) by the diameter of the
wire in cm. (0.0775) and then square the result to get
2424847. Divide this by 18676 ** (for plain wire of density
7.6 g/cc) and you will get the tension in lbs (133). If you
were to substitute a #13.5 wire (0.800mm.) you would raise
the tension to 143 lbs.
In brief the formula for the calculation of the tension is
therefore:
( f l d ) ^2 (frequency x length x diameter all squared
________
K divided by a constant depending on the mass
per unit length of the string.)
For the covered strings a rough value for K (quite adequate
for all practical purposes) is 20,000.
Thus you have, say a covered string of overall diameter
6.00mm on bottom A which has a speaking length of 1170mm.
On a simple calculator do this:
27.5 * 117 * .6 * = / 20000 =
The result is 186 lbs. **
As to the case of the old Steinway upright, I would disagree
with anyone who says the bass string scale cannot be
improved upon. Unfortunately you are stuck with only ten
singles where 12 or more would be preferable on a scale of
this length. After many decades living in the 1870's
Steinway have at last realized that their bass scales might
be changed and I notice double covered strings (Horror of
horrors, dear Theodore) on new uprights. You can
double-cover the last ten notes if you like and aim for
tension on note 1 of 180-200 lbs and on note 10 of 260 lbs.
A good scale on any piano with a speaking length of 120cm
for A1 would be 12-15 singles and 12-15 bichords with
tension rising though the singles from 200 to 260 lbs. and
all the bichords at 180 lbs. This is not possible on the
old Steinway upright. I would set note 1 at 180-200 lbs and
note 10 at 240 lbs. Note 11 cannot be given 180lbs without
making it "barky". I would recommend a rise from 140 lbs to
170lbs. through the bichord section. I don't have the
scales I have used to hand since I am at home, but I'm sure
it would be something like this. I can easily send you a
couple of suggested scales if you like. You would need to
tell me the speaking lengths of note 1 and note 26 so that I
know which model it is.
One thing I do know about this piano - the use of a #22 core
for note 10 (single-covered) finally purifies the note. The
original core is #18 and sounds awful.
|: I would also appreciate recommendations of pitfalls to
|: avoid when working with a Steinway upright of this period.
|: Does anyone have a preferred brand/supplier of hammers
|: suitable for this piano?
Nothing is better that the brown wood impregnated hammers
from Japan (I forget the name but it's something like
Imategawa). I believe Schaff are the US. agents and in
Europe Danielsen. Get them unbored and recalculate the
boring angle. Steinway's original boring (hammer
over-centring) seems crazy and I have never worked out why
they did it. Rationalizing the boring does no harm to the
tone. The strike line must of course remain sacrosanct.
|: someone else hang the hammers as I don't have a drill
|: press. What should I watch out for in replacing the
|: hammers and hammer butts?
If you have the two-forked horizontal flange then what you
should watch out for is your sanity! - especially if you are
reboring the butts for new shanks. I would recommend
fitting one note at a time and regulating as you go along
taking special care with the shimming of the flanges and all
the alignments. This is not an action for the fainthearted.
JD
--
** PS. This formula is derived from the general physical
formula for vibrating strings which states that Frequency =
half the length in cm. multiplied by the square root of the
tension in dynes divided by the mass per cm. length :
F=1/(2*L)*SQRT(T/M).
The value of K is as follows for a series of relative
densities of the string considered as a uniform cylinder
containing steel wire, covering wire and AIR.
RD K
____________
6.50 21837
6.60 21506
6.70 21185
6.80 20873
6.90 20571
7.00 20277
7.10 19991
7.20 19714
7.30 19444
7.40 19181
7.50 18925
7.60 18676
7.70 18433
7.80 18197
7.90 17967
8.00 17742
8.10 17523
8.20 17309
8.30 17101
8.40 16897
8.50 16699
8.60 16504
8.70 16315
8.80 16129
8.90 15948
9.00 15771
________________________________________________________________________
Delacour Piano Services - 34 Station Road, Parkstone
Poole - Dorset BH14 8UD - England +44 1202 731031
Bass String Manufacturer - Piano Technician
________________________________________________________________________
This PTG archive page provided courtesy of Moy Piano Service, LLC