Pianos have some 10,000-12,000 moving parts. These are designed to work well together, but there are many things that affect how they work together. Among them are age, felt and hammer wear and tear, humidity, and temperature. Regulation is the process of adjusting the piano mechanism (the action) so that it plays with optimum power, repetition, and evenness of touch. The piano is also adjusted to provide "aftertouch". This is a comfort zone in the dip of the key after the action has done its work of propelling the hammer to the strings. It is just a small amount of extra key dip after everything in the action has done its thing, usually around 0.030-0.050 inch. The "things" that have to be accomplished are:

• The hammer is driven toward the strings under power, but the push is removed about 1/16 - 1/8 inch from the strings. This is termed escapement.
• The hammer then rebounds off the strings and is trapped by backchecks at about 5/8 inch off the strings.
• The jack, which pushes the hammer to the strings, must escape far enough away from the hammer to prevent "bobbling" or unwanted repeated hammer strikes (see photo).
• The dampers have to turn the sound off effectively.
• The pedals have to work with the right amount of lost motion, about 1/4 inch on the damper pedal and negligible lost motion on the soft pedal.
• The keys have to operate the dampers correctly.

Regulation is a very involved and detailed process. But the product is usually worth the work.

In this photo, the key is depressed and held, the hammer is in check, and the jack (arrow) has escaped from the hammer butt leather by about 1/16 inch. Not shown in the photo, the hammer above is 5/8" off the string. This vertical action model is well-regulated.