Fig 1Grand action, one keyHover to press · click or 1–6 to strikerest · hammer 46.5 mm below the strings
Hammer: thrown free 2 mm before the stringsKey, wippen, jack, repetition lever and damperThree C6 strings, 190 mm speaking length, 90 kgf eachA single C6 key of a grand action on a bench. The key dips 10 mm; behind the balance rail the capstan lifts the wippen and its jack pushes the hammer through a 46.5 mm blow. At 8.9 mm of dip the jack toe meets the let-off button and the jack slips out from under the knuckle with the crown 2 mm short of the strings: the hammer flies the rest of the way on its own, rebounds, and the backcheck catches its tail about 15 mm below. Release the key a little and the repetition lever lifts the hammer back to drop height so it can strike again before the key is fully up. Past half the dip the key tail lifts the damper off the strings; let the key go and it falls back and stops them. A blow takes 8 ms at ff and 60 ms at pp, so strikes run in slow motion (factor in the readout); the string's motion is drawn six times larger than life.