Compare the three cuts of actions in the study of this lesson.
The main constituent parts of the square action are similar in appearance to those of the upright; in fact, most of the parts are the same in name and office. However, the parts are necessarily assembled very differently. In the square action, the hammers strike in a vertical direction, while in the upright they strike in a horizontal direction; the motion of the key being the same in both.
Of the three types, the square is the simplest action, as many of the parts seen in the upright and grand are entirely absent in the square.
Beginning with the key, it has its balance pin, guide pin, cushions, etc., practically the same as in the other types.
The bottom, or key rocker, is reversed in the square; the end transmitting the motion being nearest the performer.
The extension and wippen are absent in the square, as the jack is attached directly to the bottom or key-rocker.
The back check is screwed to the key, and as the hammer head rests against it after striking, the use of the contrivance called the back catch in the upright is unnecessary.
Action of the Square Piano.