The hammer: what the key finally throws at the stringsKey, jack and damper: the parts you can watch moveOne key of a grand piano, cut away and drawn to scale in millimetres with simplified proportions. The key is a see-saw: its rear end lifts the wippen, the wippen lifts the jack, and the jack pushes the hammer's roller until it slips out, here when the key is about 6 mm down of its 10 mm. The hammer flies free to the strings and a repetition lever holds it just under them while the damper is lifted off. A key pressed too slowly makes no sound: the hammer falls short.