Grand Regulation In Detail - Jack Adjustment - part 10

I pointed out in the past that we really do not set the jack height, as the jack is not variable in its height. Rather, we set the height of the repetition lever relative to the top of the jack. However, I have always called this regulation setting the jack height, and I intend to continue to do so. The specification in regulating is to have just a fraction of space between the top of the jack and the bottom of the knuckle with the whippen at rest. This can be compared to setting the lost motion in a vertical piano. However, in a grand the amount of space needed is even less than in the vertical.

Before taking the action completely out of the piano to adjust all keys for the jack height, I like to set sample keys for blow, let-off and drop, as well as jack height. Doing this first and proving these sample keys with aftertouch insures that after all of the steps in Section IV are regulated, the piano will play properly.

In order for the jack height regulation to be stable, the repetition springs must be strong enough to support the hammers. We have all seen hammers that do not return to the same height after each time they are played. This can be caused by either too much lost motion between the top of the jack and the knuckle, or by repetition springs that are too weak.

Assuming that the repetition springs are strong enough, the culprit is the jack height. As well as causing an uneven hammer line, too much lost motion also causes a loss of power. On the other hand, too little space will not allow the jack to return under the knuckle as fast as it should (or not at all) and hence cause faulty repetition. Some technicians set this measurement by feeling the top of the jack versus the side of the balancier window where the jack sits. The specs call for a 0.2mm (or a paper’s thickness) space that the jack should be below the window.

This is fine if the piano being regulated is brand new or if the knuckles have just been replaced. Under these conditions, the surface of the knuckle is very even across the face where the jack contacts it. If the knuckle is not new, chances are that the leather has begun to get grooved in the middle from the force of the jack hitting it. To obtain the proper space between the jack and a grooved knuckle will require that less than a 0.2mm measurement be used. In some cases the top of the jack may have to be even with or higher then the balancier window. With a grooved knuckle, there is only one way to regulate. That is by using a process called “winking the jack”.

With the whippen at rest, gently slip your finger in between the top of the jack tender and the bottom of the let off bottom. Slowly depress the jack tender as if it were going through the process of let-off. Be careful not to push down on the whippen while tripping the jack. Depending upon the type of action you are working upon, you may see the hammer “wink” or not! By “wink” I mean that the hammer will fall slightly lower than its neighbours. Sufficent space must be allowed for the hammer to fall, so the hammer rest rail must be set a shanks diameter below the hammershank at rest. If the action has hammershank rest felt instead of a rest rail, either raise the shank or remove some of the rest felt.

For some unknown reason, some makes always give a perfect little “wink” for this test, but others are not as reliable. Therefore, ...

 

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