The system of lever trains between the hammers and keys of a piano whereby the finger movements at the keys are transferred to the hammers and dampers that produce tones from the strings and mute them, respectively.
In other words, the moving parts under the hood!
What makes a "good" action?
Although individual preference is the deciding factor in determining a "good" action from a bad one, there are a number of mechanical tests that can be performed to get a good idea of how well an action is performing. First, lift the top of the piano to allow you to see what is going on inside when you perform these tests.
- Slowly depress a key while watching its corresponding hammer. The hammer should start to move when the key is depressed approximately 1/16th of an inch. If it takes much more travel then this before the hammer starts to move, the action needs regulation (adjustment). Excessive travel is called "lost motion".
- Now repeat the same process , but this time watch the damper (the wooden block with felt on it that is located below the hammer and normally rests on the string).
The damper should pull away from the string when the key is pushed halfway down.
- Next, strike a key and watch the hammer travel to the strings. It should travel in a straight line (not moving to either side) and strike all three (if you are playing above middle C) strings squarely.
- Again, slowly depress the key and watch the hammer, is should move to within 1/8th inch of the strings and then release itself back away from the string. If the hammer did not release itself it would mute the string as long as the key was depressed.
These are just a few of the simple tests you can perform to determine if your piano action needs regulation. If you suspect that your action needs work, contact you piano tuner.
For more on how an upright action works, see How a Piano Works