The piano action mechanism

In addition to considering the musical properties of the piano, we must also take into account its mechanical characteristics.  The key-bed and other tray action parts, as well as the pedal trap mechanism and its related parts, are complex working assemblies. These impart the intentions of the pianist to the musical parts of the piano.  With few exceptions these parts are made of wood. The bearing surfaces and stationary contact points are made of various grades of pressed or woven cloth, and the hammers are covered with specially processed wool felt.

The piano’s keys are actually simple, type-class A, levers.  That is, the fulcrum or balance point is near the center of the length of the key with the effort (pianist’s fingers) and resistance (key’s action) on opposite ends.  Each key is made of a dimensionally stable material–usually wood–with its own guide pins and felt bearing surfaces, and each one can be regulated independently. The note action assembly or “whippen” is the escapement device which is activated by the resistance end of the key.  This part moves the hammer and its shank carriage piece and is responsible for the hammer’s strike and immediate release.  This produces the bell-like sounds we recognize as piano music.  The damper action is also activated by the key as it is depressed, and it silences its note as soon as the key is released.  Depressing the pedals causes the (damper) action to sustain, soften or hold some or all of the notes during playing.  This enhances the agogic style and dynamic intentions of the player.


Together, these mechanical parts of the piano form a complex machine composed of hundreds of wooden parts and assemblies along with a few metal and/or plastic units.  Some have carefully machined working profiles with tiny axles and felt covered bearing surfaces, and many have small springs, adjustment screws, and pads of leather or felt.  The hammers and dampers are covered with finely milled wool felt, and the keys and pedal parts are very carefully made to accommodate the players movements.

Maintaining the piano’s “machinery” at all times is important in order for it to perform as expected.  It is recommended that the piano be tuned and serviced regularly by a qualified piano technician to preserve both its tonal stability and mechanical integrity.