Piano keys can stick down or become sluggish for a seemingly infinite array of reasons including, but certainly not limited to; foreign objects caught between the keys, jammed or broken interior action parts, warped keys rubbing together, broken keys, and a whole variety of causes associated with moisture. Cross section of a piano key Unfortunately, it may not be readily apparent whether the cause of a sticking key is in the piano action or the key itself. To determine this it is necessary to have access to the action, usually calling for the service of a professional tuner.
However, a common cause of keys that stick down (or fail to sound on a repeated stroke) is moisture in the key bushings. As can be seen in the cross section drawing, 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 serves to keep the key from wobbling sideways. Both pins extend through channels in the key which are lined with a thin felt bushing cloth (shown in red in the drawings).
Although the balance pin rarely causes much problem, the guide pin can be quite troublesome, especially in very humid conditions. Even a small amount of moisture trapped in the bushing can swell the felt and cause it to grip the pin too tightly. The result can be a key that either sticks down, or fails to return on the upstroke enough to allow the action parts to get back into position for a repeat stroke. This is a frequent condition on new pianos since the bushings are a very tight fit to begin with, in order to allow for eventual wear. To properly remedy this condition a piano technician removes the key and uses a special tool to compress the felt.
However, 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 indicated 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 quite thick, but remember the point is to compress the felt bushing, not the key wood. Also be very cautious when applying this technique to the black keys; the wood
is much thinner in these keys and too much pressure could risk cracking the wood. The object here is to just compress the felt enough to free the guide pin. 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 and the bushing compressed. 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.
However, a common cause of keys that stick down (or fail to sound on a repeated stroke) is moisture in the key bushings. As can be seen in the cross section drawing, 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 serves to keep the key from wobbling sideways. Both pins extend through channels in the key which are lined with a thin felt bushing cloth (shown in red in the drawings).
Although the balance pin rarely causes much problem, the guide pin can be quite troublesome, especially in very humid conditions. Even a small amount of moisture trapped in the bushing can swell the felt and cause it to grip the pin too tightly. The result can be a key that either sticks down, or fails to return on the upstroke enough to allow the action parts to get back into position for a repeat stroke. This is a frequent condition on new pianos since the bushings are a very tight fit to begin with, in order to allow for eventual wear. To properly remedy this condition a piano technician removes the key and uses a special tool to compress the felt.
However, 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 indicated 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 quite thick, but remember the point is to compress the felt bushing, not the key wood. Also be very cautious when applying this technique to the black keys; the wood
is much thinner in these keys and too much pressure could risk cracking the wood. The object here is to just compress the felt enough to free the guide pin. 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 and the bushing compressed. 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.
