David asked me to forwardthis while he's getting his internet connection set
up. (His address: stanwood@tiac.net) Bear in mind one thing. Leverage can be
measured either lineally or by mass. Either has its difficulties in getting a
sharp resolutionh on your measurements. Lineal is great when relating key dip
to hammer blow. But when you're wondering why a given weight of hammer works
on one action but not another of the make, model and vintage, leverage by
mass is what you want. (BTW, Mcheal Wathen was measuring his knuckle
configuration leverages by mass. See his 9/14/94 post.)
You might wonder why David chooses to call a leverage on the low side
(5.0-5.7) "Full", and on the high side (6.3-7.0) "low". The labels certainly
don't relate directly to their numerical values. Think of them as refering to
how limited they are in the size of hammer they can drive.
One minor footnote: you'll find in the STRIKE WEIGHT RANGE GUIDELINES: table
an "=20", and the Leverage*Strike Weight Table, several "A=6"'s. Don't let
these confuse you, they're apparently leftover from the character set of the
word processor with which he composed the letter.
Don't worry if you have questions. Tha's what pianotech is for.
Happy Illuminations
Bill Ballard RPT "I gotta go ta woik...."
NH Chapter Ian Shoales, Duck's Breath M. Theater
---------------------
Forwarded message:
From: stanwood@tiac.net (David C. Stanwood)
To: yardbird47@aol.com
Date: 95-01-11 11:21:07 EST
Dear Vince,
Thanks for your question.
<What things tell you when the capstans should be moved?>
Answer: We move the capstan line in or out when
touchweight indicators tell us the action is under or
over leveraged.
Explanation:
To determine if an action is over or under leveraged we
measure the leverage and if it does not conform to our
standard then we change it.
Leverage may be controlled to some degree by choosing
parts wisely. Post '84 Steinway parts with the knuckle
further out yield maximum parts leverage. Pre-84
Steinway parts with the knuckle further in yield minimum
parts leverage. Japanese, Renner USA, and most others
fall in between.
******************************************
Warning!!
Pre 84 Steinway parts with stock Steinway hammers are
likely to produce heavy action. The owners of Steinway
recently told me that "pre 84" does not mean these
parts should be automatically used on all pianos made
before 1984.
Perhaps they should change the name to "low leverage"
******************************************
If the leverage cannot be brought to a desired level by
changing parts then the problem most likely is in the key
ratio. Key ratio is nominally 2:1 for modern pianos, but
for a variety of reasons this is often not the case.
Actions with inappropriate key ratio may be corrected by
moving the capstan line in or out. This involves altering
the wippen heel so that the capstan is centered on the
cushion felt and the capstan contact point is in a line
between the wip center and the balance point of the key.
To measure leverage we use a touchweight parameter called
strike ratio.
*Strike ratio is the amount of weight needed to balance
one gram of hammer weight at the front of the key.
Strike ratio gives an indication of how fast the hammer
moves in relation to the downward movement of the key. It
is therefore a useful indicator of the dynamic quality of
the action. In fact we have found that the dynamic
playing quality of the action may be predicted if the
strike ratio and the hammer weight are known. More on
hammer weight later...
The strike ratio level of a piano action is determined by
measuring strike ratio in sample keys and calculating the
average. For minimum significant accuracy we use a sample
of six measurements on notes 16,17,40,41,64,65. More
accuracy is attained by measuring all the c-c#s. Maximum
accuracy is attained by measuring all 88 notes.
*****Strike ratio is determined by finding the strike
balance weight and dividing it by the strike weight.*****
Measuring strike balance weight:
1. Lift up the hammer and shank.
2. Place temporary weights on the back of the key such
that the balance weight of he key and wippen becomes
zero.
3. Lower the hammer and shank back down
4. Measure upweight and downweight.
5. Calculate strike balance weight as the average of
upweight and downweight
*Strike weight is the amount of weight that hits the
string Measuring strike weight:
1.Remove the shank from the rail
2.place a hard felt wedge on the pan of a digital scale
and tare to zero.
3.Place the striking surface of the hammer face down on
the felt wedge such that the strike line of the hammer
is resting on the knife edge of the felt wedge
4.Tip up the flange so that it is oriented vertically,
5.Rest the bottom end of the flange on a roller bearing
such that the axis of the roller bearing is aligned
vertically with the axis of the center pin, with the
shank perfectly horizontal.
6.The resulting scale reading indicates the strike weight.
Again: Strike Ratio =3D Strike Balance Weight/Strike Weight
Acceptable strike ratio levels fall in a range from 5.0 to
7.0 If strike ratio level is below 5.0 the hammer will
move too slowly in relation to the key and excessive key
dip will be required to regulate the action. If strike
ratio level is above 7.0 the hammer will move too quickly
in relation to the key and excessively shallow key dip
will be required.
We recommend 5.5 as a modern standard for strike ratio.
The best pianos surveyed were close to this level. The
5.5 standard emulates the Hamburg Steinway which is the
only piano surveyed that was consistently at this level
with consistently the best action.
*********************************
I offer the following range guidelines for strike weight
and strike ratio. These ranges are the result of 4 years
of survey and analysis of piano actions.
The primary touchweight studies were carried out by myself
and the following technicians:
Russell Gordon RPT
Tony McKenna, Belmont Mass
Bill Ballard RPT
John Foy RPT
STRIKE WEIGHT RANGE GUIDELINES:
Note 1 22 44 66 88
=20
14.8-------13.7-------12.1--------9.8---------6.9
F U L L T O N A L P R O J E C T I O N
12.4-------11.5-------10.2--------8.3---------5.8
M E D I U M T O N A L P R O J E C T I O N
10.3--------9.5--------8.4--------6.7---------4.6
L O W T O N A L P R O J E C T I O N
8.0--------7.4--------6.5--------5.2---------3.5
STRIKE RATIO RANGE GUIDELINES
Full Leverage 5.0 - 5.7
Medium Leverage 5.7 - 6.3
Low Leverage 6.3 - 7.0
We have found that if a full ,medium, or low strike ratio
is matched with a full, medium or low, strike weight a
normal feeling action will result when balanced to a
normal upweight and downweight. Problems are likely when
ranges are mismatched. For instance: Full projection
weight hammers matched with low leverage will yield a
piano with high inertia that plays like a truck, or: Low
projection weight hammers matched with full leverage will
make for an action that is excessively light with low=20
inertia. Refer to the table below:
TABLE
Dynamic touch as a function of Strike Weight and Leverage
(Inertia)
Leverage
S =A6 LOW =A6 MEDIUM =A6 FULL =A6
t ------+----------+----------+----------=A6
r LOW =A6 Medium =A6 light =A6 Xlight =A6
i ------+----------+----------+----------=A6
k MEDIUM =A6 Heavy =A6 Medium =A6 light =A6
e ------+----------+----------+----------=A6
FULL =A6 Xheavy =A6 Heavy =A6 Medium =A6
W ---------------------------------------+
t
One final note: The hammer weight may be found by
subtracting the shank strike weight from the strike
weight. The shank strike weight is the weight of the
shank taken at the strike line radius.
Shank strike Weight is generally around 1.8 - 2.0 grams
David C. Stanwood
Copyrights reserved by David C. Stanwood
The document may not be reproduced in any other form other
than print outs of this document in this form for personal
use.
=1A
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