Typical Upright Piano Action
the key is pressed, it rocks on the centre rail, moving upwards
at the back. In so doing, it raises the sticker and whippen.
The whippen operates the jack, which in turn pushes the hammer
butt. The butt pivots on its flange and moves the hammer towards
the string. When the key is half way down, the damper spoon
engages with the damper lever, lifting the damper off the strings.
When the hammer is almost to the strings, the jack heel meets the set-off
button, and as the whippen keeps moving up, the jack pivots and moves
out from under the butt. The hammer then continues under its own inertia
to the string, instantly rebounding. The balance hammer is caught by the
back check and is held in this position as long as the key remains
When the key is
released, the whippen drops, the back check releases the balance hammer,
the bridle tape exerts a tug on the butt, and with the help of the
butt spring, the hammer returns to the hammer rail (not shown). The damper
spring returns the damper to the strings, and the jack spring returns the
jack under the butt, ready for the next repetition. This entire sequence
is momentary, allowing rapid repetition of the notes.