Piano Mechanism and Keyboard Action

Point number 1: This consists essentially of a compound lever ; the end which is presented to us of this lever is faced with ivory or ebony, while the other end carries a wooden hammer, covered with layers of felt. The mission of this leverage-system is to render great speed at the hammer-end easy of at. tainment, so that this can there be transmitted to the string, As the fulcrum of this leverage-system is far closer to oui end of the key than to the hammer end of it; it follows, that the hammer moves through some two inches of space, with correspondingly increased speed, for the mere f inch or so that the ivory-end of the lever can be depressed.
The depression of our end of the key beyond that depth is arrested by a felt pad the "key-bed" as it may conveniently be termed. The mechanism is so adjusted, that the hammer gives its energy up to the string just before the key reaches this pad.
Here we realize, that all misdirected effort, on the part of the performer (i.e. : effort ill-timed or ill-directed in its application to the key during descent) is spent merely on these key-beds. The energy intended to create sound is thus more or less lost, and the mechanism of the instrument is over-driven to its manifest injury, and to the detriment of the quality of the tone. Hence it may be useful to regard the key as a See-Saw ; for the key is so weighted, that although it seems level or nearly so when at rest, yet it is in reality tflted-up toward us, ready to have its other end, the hammer-end, tilted up during the act of soundexcitation.

The most important of the several devices with which this leverage-system is provided is the "Escapement". This enables the hammer to fall .away from the string the moment its mission is completed; and this, although the player may retain the key in its depressed condition. We should however be unable to repeat the note, without first allowing the key to rise back fully to its surface level, if this "escapement" allowed the hammer to fall completely back to its place of rest. To obviate this inconvenience (and consequent risk of non-repetition of the note) all good modem Grands and some Uprights are provided with a supplementary device. This device, while it allows the hammer to rebound with (and from) the string, and thus leaves the latter free to continue in vibration, yet keeps the hammer fairly close to the string's surface so long as the key is kept fully depressed ; the slightest rising of the key from its depressed condition, here suffices to enable one to repeat the note ; for the hammer does not in this case fully fall back, unless the key is also allowed to rise beyond a certain point.
An "action" or mechanism) thus provided, is termed a repetitton-action; a term that must not be confounded with "check-repetifion," or "check "-action, which is quite another thing.

In the older instruments, the hammer was left free, after its rebound from the string. This rendered it liable to bound back against the string on its own account, re-striking the string once or twice before finally coming to rest. The tone was thus ruined, since such re-striking would not be likely to occur in re-enforcement of the string's movement ; intentional rapid repetition was also but a precarious matter under this arrangement.
A "check-repetition" was consequently devised. A "check" a little wooden jack covered with leather or felt is here provided, this rises as the key descends, and is so adjusted that it catches a projection on the end of the hammer, when this falls back, thus precluding* any further motion, until released by a sufficient ascent of the key.
6. "We see, therefore, that a "repetition-action" renders easier quick repetitions of the same note; whereas, a "checkrepetition-action" prevents the hammer from rebounding- on its own account, and thus marring the sound.