Sticking and sluggish keys.

Piano keys can stick down or become sluggish for many reasons, including foreign objects caught between the keys (see my article on retrieving things from piano actions), jammed or broken action parts, warped keys rubbing together, broken keys, and problems associated with moisture.Cross section of a piano key

But it may not be obvious if the cause is in the piano action or the key itself. To find out you will need access to the action, usually calling for the service of a piano tuner.

However, a common cause of keys that stick down (or fail to sound on a repeated stroke) is moisture in the key bushings, and you may be able to correct this yourself.

As can be seen in drawing above, the key is guided in its up and down motion by two metal pins extending up from the keybed; a balance pin in the center of the key (at the balance point where the key rocks on a falcrum), and a thicker guide pin near the front of the key which keeps the key from wobbling sideways. Both pins extend through channels in the key and are lined with a thin felt bushing cloth (shown in red in the drawings).

Although the balance pin rarely causes problems, the guide pin often does, especially in humid conditions. Moisture trapped in the bushing can swell the felt and cause it to grip the pin too tightly. The result is a key that sticks down, or fails to return enough to allow the action parts to get back into position for a repeat stroke.

This is often the case on new pianos since the bushings are a very tight to begin with to allow for wear. To fix this a piano tuner removes the key and uses a special tool to compress the felt.

Sometimes the pin can be freed by slightly compressing the bushing by hand. Grab the key at the front and move it laterally back and forth (as shown by the arrows in the following drawing) to press the pin against the felt. Naturally you cannot see the pin without removing cabinet parts, but if you attempt to move the key sideways you will feel the resistance of the guide pin.

Do not apply great pressure, but slowly and firmly move the key back and forth several times and press the pin against the felt to compress it.

On white keys you may use moderate pressure since the wood in the key is fairly thick, but remember, the point is to compress the felt bushing, not the key wood. Be cautious when applying this technique to the black keys as the wood is much thinner and too much pressure could risk cracking the wood.

Compressing a bushing by moving a key laterally Compress the felt enough to free the guide pin in the bushing. If moving the key laterally three or four times doesn't do the trick, forget it. The problem is probably elsewhere.

If there is too much swelling of the felt, or the problem is in the action, you will be obliged to call a piano tuner and have the key removed. If sticking keys are a consistent problem with your piano, a dehumidifer installed inside the piano may solve the problem. Check with your piano tuner for info on dehumidifing systems.

Another often overlooked source of sticking keys, particularly on new pianos where the wood is still curing, is a warped or out of position keyslip, the thin strip of wood which runs parallel with the keyboard in front of the keys (see drawing below).

The gap between the keyslip and the keys is close, an eighth of an inch or less. Sometimes moisture will swell the wood, or a player inadvertently press against the keyslip and move it forward to rub against the keys.

This problem occurs on all model pianos, but is especially common on grands where the keyslip is removable to allow the action to be taken out of the piano.

Sometimes all that is required is to grip the keyslip with your fingertips and gently pull it back toward you. If the wood is too badly warped it may be necessary to loosen the screws under the keybed and apply cardboard shims between the keyslip and endblocks to space it away from the keys.

A warped keyslip can cause sticking keys

Another (admittedly more desperate) measure to remove moisture from the key bushings is to use heat from a portable hair drier. Put the drier blower on high and move it laterally across the front of the keys and keyslip for five or ten minutes. Sometimes the heat will dry out the bushing and free the key. It's worth a try anyway.

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