A new method for reduction of the friction in a grand action.
After the introduction a couple of years ago the Magnetic Balanced Action, which now is sold by Fazioli and Petrof and also in the U.S.A. as retrofit kit by International Brokers Inc., we like to introduce you to a new method of friction reduction in the grand piano action.Like in the Magnetic Balanced Action this new method, called Magnetic Friction Reduction or for short MFR, is based on the force which can be delivered by magnets. In this case simply two magnets per key are applied.
The main cause of friction in a grand action is, as anybody skilled in the art knows, the interaction between knuckle and repetition lever and at the instant of escaping of the jack between knuckle and jack.
Several attempts have been made to reduce this friction, mainly by using materials with a lower friction coefficient at the top of the jack and at the top of the repetition lever.
Also is proposed a rotating knuckle, to reduce this friction.
In the following description a patented method will be described which not only reduce the friction, but also reduce a considerable amount of the required lead especially in the bass keys. This reduction has an advantageous effect on the dynamic behaviour of those keys, because the smaller amount of lead leads to a smaller inertia of the key.
In figure 1 is shown a part of a grand action.
Added to the hammer shank is an adjusting screw 1 and attached to this screw a small permanent magnet 2. On the repetition lever is also mounted a support 4 and on this support is attached another permanent magnet 3.
The facing areas of the two magnets have the same polarity, so they excersise a repelling force on each other.
As a result of this repelling force the pressure of the knuckle on the repetition lever is reduced. It is well known that the friction between two areas is proportional to the force these areas apply on each other, so by reducing this force also the friction is reduced. When the air gap between two repelling magnets increases, the repelling force decreases. In the rest position of the key the magnets are, as can be seen in figure 1, not exactly opposite to each other. When the key is pressed down, the air gap increases, but at the same time the magnets come more and more in line. This effect continues till the moment of escape of the jack, then the magnets are in line, as is shown in figure 2.
This effect compensates the loss in repelling force caused by the increasing air gap.
The reduced friction reduces the amount of lead in the front-end of the key. But an other effect plays also an important role to reduce the lead in the front-end of the key.
The downward force caused by the hammer is transferred to the whippen and the key not only by the knuckle, but also partially by the repelling force of the magnets. One can say that on the spot of the magnets a virtual knuckle is active. This virtual knuckle is closer to the hammer and to the rotating point of the whippen than the real knuckle. The result is, that part of the downward force caused by the hammer, equal to the repelling force of the magnets, is transferred to whippen and key at a favourable spot compared to the real knuckle. This gives an additional decrease in the amount of lead to be mounted in the front-end of the keys. A further advantage of the described system is that due to the fact that the pressure of the knuckle on the repetition lever is reduced, deformation of the knuckle will be postponed.
A bass key was equipped with the magnets and the key was weighted with lead to get a down weight of 52 gram.
Then the uplift was measured which proves to be 34 gram.
The calculated friction is then: (52-34)/2=9 gram.
Then the magnet in the hammer shank was removed and again the down- and up-weight was measured. These values where: Down weight: 74 gram; up-weight 48 gram. The friction is then (74-48)/2=13 gram.
Putting more lead in the key brings these values to 52 for the down-weight and 26 for the up-weight. Calculating again the friction gives (52-26)/2=13 gram.
What does this mean.
First using the MFR the uplift is improved from 26 to 34 grams, or in other terms, the friction is decreased from 13 to 9 grams.
Secondly the amount of weighting the key is decreased with 22 gram, what is far more then expected from reduction of the friction.
The toneweight, that is to say the weight required to produce a ppp tone is about plus 11 gram more than the downweight. By a conventional action is this about 18 gram. A profit also of 7 gram, that is to say that by a normal downweight, the action gives a lighter feeling by pianissimo playing. Because of the decreased friction the upweight is higher. Because of that it is possible to weight the instrument about 8 gram less than normal, which is comfortable for children and gives people with muscle problems to continue playing.
I think I have provided a relatively simple and favourable method to overcome the difficulties concerning the uplift weight, which often are present especially in the bass of a grand piano.