Key height is the height above the key bed that the key is set to best perform the task of transferring the energy of the player to the hammer. This in turn strikes the string, reed or tine. it is essential for proper regulation of a piano because even key height allows all other parts of action following to be evenly regulated. The first thing a musician does when they play is press the key when it is as rest position, so key height is the first aspect of regulation. Individual key height is adjusted by inserting or removing punchings at the balance rail for the white and black keys. More general key height can be adjusted by shimming the key bed, which involves inserting shims of paper underneath the key slip. An even leg height also makes the keys look nice and even, which makes the piano look regulated.
The other critical function of key height is its effect on key dip. Key dip is affected by key height because the higher the key is the further the key travels before full key dip is achieved. Whilst key dip affects more aspects of the piano action directly, key height and dip have an intimate relationship.
Hohner Clavinets are a little different. The key height is adjusted by moving a metal strip which houses the key bushing. Ideally this strip is set at a 90 degree angle. Individual key height on Clavinets is usually undertaken to level the keys, as some can sag after years of playing. General key height can be adjusted by the key frame. This is done by raising or lowering the washers, on the key screws at either side of the keyboard. Sometime adding or removing extra washers is needed. Note that adjusting key height open clavinet affects key dip, as they are locked together.
