Key Bushing Replacement

Key bushings are small pieces of felt glued inside the wood part of piano keys. They enable the key to slide with very little friction against metal pins that keep the key in place. As a piano ages and is used, gradually the key bushings wear and the keys begin to wiggle from side to side and even tip to the right or left.

In higher quality pianos, key buttons are used to house the bushing. Key buttons at the factory are bushed first, then glued on the flat keystick. The lump on top of the key in this picture is a key button.

The keys are the most important parts of a piano because this is where we control our music. Everything is built upon the movement of the key. It is the only place we touch the piano (besides the pedals). Suffice it to say that if the keys are not right, then nothing else can be.

As key bushings wear there is a gradual loss of control, wiggle and knocking noise can be distracting. Fingers begin to stumble because piano keys are not precisely where they are supposed to be, and children do not easily develop the ability to play without watching their hands. Because key bushings are made of wool felt, moth larva have been a big culprit of key bushing failure. Moth larva eat wool and cause holes, riuning the support and cushioning effect that prevents noise and holds things in place.

Only by replacing the key bushings can you get back the firm control that the piano had when it was first new; some cases…even better control. The reason why I say this is important. Well-meaning piano technicians have damaged MANY pianos by use of a tool advertised to "tighten" key bushings. This tool is still in WIDE USE in the industry. I will discuss this at the end of this page.

After replacing key bushings, the keys must be fitted to the pins. This will provide just enough squeezing pressure from the bushings without being too tight. The balance rail hole in the bottom of the key must be sized properly as well.


In the preceding picture to the right, the left 2 keys are untrimmed. Because the bend in the fabric is the control point where the technician makes the fitting possible, on some pianos the keys must be left untrimmed or the keys will be too loose. On other pianos there is a small cut-out window underneath the key button that provides enough bend in the fabric to allow a control point. These type of keys must be trimmed to provide only one control point. Trimming allows for a cleaner, neater look as shown by the 3 right keys in the same picture.


Damage

As I mentioned earlier, only by replacing the key bushings can you get back the firm control that the piano had when it was first new; some cases…even better control. The reason why I say this is important. Well-meaning piano technicians have damaged MANY pianos by use of a tool advertised to "tighten" key bushings. This tool is still in WIDE USE in the industry. They still sell it and teach it in some schools of piano technology.

These tools (seen below) are designed for use with a hammer. The center part is supposed to keep the mortice open while two chizel edges break the wood of the key or key button, splitting it at the top, but still keeping it attached at the bottom, so the broken pieces shift, but don't actually fall off. It is a cheap, destructive way to tighten key bushings.


Because the broken wood is always shifting and the wood swells and shrinks through changes in humidity, consistency in touch and control is impossible and the broken parts must be fixed with an ultra thin epoxy or the whole keyset re-made which costs around $1,000.00.

A correlation to using this tool would be when a wheel on your car begins to wobble because a lug nut is missing. You can take it to a mechanic that puts a new nut on and tightens the others up, making sure they have the right torque, or you can get a mechanic to take a sledge hammer to flatten the threads and just make it tighter.