Touchweight Design
An Independent Introduction



Many of us are familiar with the grand piano action, comfortable with regulation and field repairs, and have some experience in voicing techniques. In the course of our day to day work we often have to deal with questions or problems relating to the Touchweight of the action. It is of course important to separate actual weighting problems from other aspects of action performance that can be associated with them.

As an  example of this is let us consider the voicing of  an instrument. It is no secret among accomplished pianists that the fingers can “feel” the “voice” of the instrument. This is experienced through the key as the hammer hits and rebounds off the strings. The hammer can feel “hard” or it may feel “soft”. A pianist might just as well use the words “light” and “heavy” too describe these same. Light = hard= bright, and heavy = soft = dark. With these kinds of descriptive words, and many others just as vague, the pianist will try and tell you something about how the piano feels and sounds. Its easy to see how one can get confused in ascertaining and diagnosing Touchweight problems when much of the terminology we use for describing weight conditions is used by a pianist to describe either weight or voicing concerns, or for that matter some combination of the two.

Once we are in the realm of Touchweight concerns however, our task is that of manipulating the actions actual weight and leverage factors so as to bring it into conformity with some predetermined specification. Traditionally this specification has been in the form of a desired Downweight, for example 50 grams. Perhaps we desire the touch of an instrument to become gradually slightly lighter in the treble. In any case it is preferable that this touch is as even as possible throughout the entire key board.

While fine piano manufactures have indeed managed to achieve a high degree of evenness in static Downweight alone, a new methodology exists for optimizing Downweight in a fully predictable and exacting way that in addition determines precisely what weight, mass and leverage characteristics the grand action will have. This has the added benefit of allowing us new latitude in deciding the general voicing characteristics of the instrument, and otherwise makes the process of voicing much easier to deal with..
 

What is Touchweight (BW) ?

Many of us are used to static up and down weight  measurements. These have traditionally been used to help us decide how much weight in the form of lead to put into the keys during the weigh off process of setting up an action.  Field technicians usually use a set of weights to measure Downweight  and Upweight  as an indication of how heavy the action is. While these certainly give us an indication, they really tell us little about why an existing action weighs what it does, and indeed can be misleading relative to the actual touch of the instrument.  Furthermore, Downweight and Upweight measurements alone give us very little information to base decisions for altering the feel of an action on. We can however,  arrive at  two rather more valuable quantities using  Downweight and Upweight.
Touchweight and Friction

Touchweight (BW)  as a concept was introduced some years ago.  It is found by adding Downweight  and  Upweight, then dividing the sum by 2..

BW = (DW + UW) / 2.

Touchweight is friction independent as will be explained in a bit.  Touchweight is quite typically between 36 and 42 grams.

Friction (F) is a valuable quantity to know as well.  Friction is found by subtracting Upweight from Downweight, then dividing the remainder by 2. Generally Friction should represent about 15 grams of “weight” in the action. More then 20 is definitely  too much, and less then 10 grams is too little in most cases.

F = (DW – UW) / 2.

The Value of Touchweight and Friction quantities

For some readers this is familiar ground, though it is necessary to understand these simple concepts to understand Stanwood’s new methodology. The rest of this article will attempt to  show some of the reasons why this is such a valuable tool to have in our toolbox of abilities.

Touchweight  is a very valuable quantity as it removes the element of friction from both the static weight measurements that comprise it. That Touchweight does not change with changes in friction is easy to see.  When friction goes up,  Downweight  goes up and Upweight will sink. As it turns out 1 gram increase of friction yields 1 gram increase in Downweight and 1 gram decrease in Upweight  so Touchweight stays unchanged. Touchweight is reflective of the overall balance present between the keys and the action, and because friction is isolated from Touchweight we are presented with an opportunity for analysing more closely the other two elements that together with friction comprise that balance. Namely action leverages and parts mass. Being able to separate and quantify these three implies the ability to manipulate them purposefully.

Knowledge of friction quantities, combined with a strong familiarity of its causes and sources is also an important diagnostic tool for any Touchweight concerns. There are many sources of friction in an action. Action centres, key pins, bushings, and the balance rail hole are familiar sources. But action friction is more complicated then this.  In general friction increases with the amount of mass in the action. One only need envision the relationship between the hammer knuckle and whippen to see the sense in this. The heavier the hammer, the more friction will be present between the jack and the knuckle. The same applies to all such moving contact surfaces. Friction is also related to leverage geometry.  The more pivot-like these leverage interactions are the less friction present. Higher leverage ratios mean more weight concentrated on a fulcrum point which means more friction at that point. All these can combine with each other in a variety of ways to create a compound friction problem.

Problems with Traditional Weigh-off methods

At this point we should be able to start seeing  some problems with looking at Downweight and Upweight alone. It is clear that if Downweight is variable with friction and friction remains an unknown quantity, then any weigh off decisions relating to the amount of lead to be put in the keys will not take into account the amount of friction present. The weigh off technician will simply add or subtract extra lead as necessary to result in an even Downweight.  This is in reality an guarantee that the key leading will be significantly uneven because we are simply counter weighting the top action as is, without really knowing anything about its weight attributes. We may achieve an even graduated Downweight this way, but the touch of the piano will vary unnecessarily.

In order to understand this better we need to think about the balance of an action. Whatever weight is present in the key must be counterbalanced by the forces working against the key at the capstan. This includes friction, action and key leverage, and the actual weights of the action parts.  Any unevenness on the one side of this equation is reflected somehow on the other.  So uneven key leading for the same Downweight specification reflects uneven weight factors on the back side of the key.

There are several reasons why this is undesirable. Lets start with inertia. Inertia is the property of any mass to resist any change in motion. Put another way, mass is a measure of inertia. The greater the mass of an object, the more inertia it has. The more inertia an object has, the more difficult it is to stop its motion,  to change the direction of its motion, or for that matter to put it into motion to begin with. There are some obvious consequences here that should be readily apparent for the case of the grand piano action.

The more mass present in a key, the higher the level of inertia, and  the slower (read  sluggish) it will react to changes in motion as is the case when the key needs to return from a quick staccato blow for example. Higher inertia also means it takes more force (read heaviness) to get a key moving in the first place.  The same may be said for all action parts. A hammer with much mass will resist rebounding off the strings more then a hammer with less mass. Obviously then any such unevenness will result in varying moments of inertia for each key, regardless of how even Downweight is.

Another mass related problem is that of how hammer mass relates to voicing. It take little imagination to see that varying hammer mass levels will challenge the skills of  the voicing technician more then if hammer mass is very evenly graduated. The attentive reader will also begin to be aware at this point of the potential for the entire voicing process inherent in this approach.

Touchweight as an aid in Voicing

The ability to identify through actual measurement the roll each of these components (friction, leverage and mass) has in the resulting Touchweight  presents us with an extremely valuable new voicing tool. Because we can easily isolate and change the weight contributions each individual action component has,  we can control to a much higher degree the general voice characteristics of the instrument while maintaining any particular action balance. This allows us to decide the general mass level of a set of hammers without having to change our Touchweight specifications. It also allows and motivates us to graduate  the individual weights of hammers to an extremely precise degree, both from an even Touchweight perspective and an even voicing perspective. Remembering that pianists can “feel” the voicing of the instrument, it is easy to see why this methodology is so valuable.
 
 

Summary

Touchweight and its counterpart Friction allow us to isolate, measure,  and control the different components of the action that contribute significantly to the actual touch of the instrument, namely weight (mass), leverage, and friction. This ability presents us with the possibility of attaining predetermined Touchweight specifications while at the same time assuring even and precisely graduated  hammer mass and counter balancing key mass.  This  enhances the even feel of the Touchweight by effectively evening out the effects of inertia. In addition, inherent in this perspective is a valuable tool for influencing the general voice of the instrument by allowing us to design in the basic mass levels of hammers independent from the desired Touchweight. Finally the insurance of  evenly graduated mass levels eases the task of the intoner (voicer) significantly, both from the perspective of the actual voicing as a technical process, and from the standpoint producing a consistent response from touch in a way more conformant to how pianists experience playing the instrument.

Richard Brekne

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