Looking At An Upright Piano Action
It is true to say that an upright piano action is a very complicated machine. There are 88 notes and each note has many moving parts. There are thousands of moving parts in one action. The action has to be regulated perfectly to allow the pianist to play with the lightest of touches or with power to achieve much louder sound effects. Either way the piano action must respond perfectly and this is done by perfect regulation. The action consists of many springs and levers to allow the key to be pressed down and at the same time send the hammer forward to make contact with the strings. The hammer cannot sit on the strings and by a an escape mechanism the hammer falls away from the strings allowing them to vibrate. To stop the sound there is also a damper that sits against the strings. This damper must lift off the string just before the hammer hits the string to allow the perfect vibrations. When the finger is lifted off the key, the damper returns to the string to cut the sound. Imagine how fast the action must be moving when concert performers are doing rapid staccatos?
Please see a one note model in action on the video link below.