Fig 1Grand piano actionPress and hold · ↓ ↑ step · 1 2 3 playdip 0.0 mm · hammer 45.0 mm from string · damper on
The hammer: lifted by the jack, free after let-off, caught by the backcheckKey, wippen, jack and repetition lever: 5.7 mm of hammer for 1 mm of keyThe string, its damper, and the plate that holds themOne note of a grand action. The key lifts the wippen, the wippen lifts the jack, and the jack lifts the hammer by its knuckle, so the hammer moves about 5.7 mm for each millimetre of key. At 7.5 mm of key travel the jack's toe meets the let-off button and tips out from under the hammer, which flies the last 2.1 mm on its own, strikes, and is caught by the backcheck on its way back. The damper leaves the string first and falls back when the key comes up. A slow press reaches let-off and never strikes.