As your Wilmington DE Piano Tuner, I am often asked why tuning pins are not simply glued in place, so the piano will never go out of tune. It is an interesting question. An appropriate answer requires some background information about the construction of pianos.
Each piano string is attached to a cast iron plate at one end, and then wrapped around a tuning pin at the other end. The tuning pin is inserted into a laminated block of hardwood, called either the “wrest plank” or the “pin block.” The wood is laminated, so that the grain of the various layers helps to grip the tuning pin. Hardwood is used, because the forces on the pin block are substantial. Typically a piano has over 200 hundred strings, each at 150 lbs. of tension. That multiplies out to 30,000 pounds of tension on a wooden structure. The pins need to be held tight enough that they will not loosen due to the string tension, but they must be loose enough to allow tuning.
The question, then, is would the piano be permanently in tune if the tuning pins were glued and could never turn. The answer is, “No.” Pianos are constantly going out of tune due to flexing of the soundboard. The piano soundboard is the structure that amplifies the sound of the strings. Without it, the piano would sound like an electric guitar that has the amplifier turned off. The soundboard is a large, thin piece of spruce that has a slight dome shape. The strings are attached to the soundboard in such a way that they have a combined downward pressure on the soundboard of 500 pounds. Because the soundboard is dome-shaped it changes size with changes of temperature and humidity. If the temperature and/or the humidity rise, the wood expands and the amount of dome increases. This change of shape increases the tension on the strings, so that the pitch rises. If the temperature and/or humidity fall, the the pitch falls, as well. Even when the tuning pins do not move at all, the piano will go out of tune. To correct for these changes, the tuning pins need to be moveable, so that the piano can be restored to proper tune.
If you have any questions about pianos or piano tuning, please let us know. As your Wilmington De piano tuning expert, I am always available to answer your questions. We also provide piano services in Philadelphia, Southern New Jersey and the Eastern Shore Maryland areas.