The pinblock is one of the most important parts of the piano. Its job is to grip the tuning pins tightly so that the piano does not go out of tune. In most grand pianos, the pinblock is not visible, but it is directly underneath the tuning pin portion of the plate. The tuning pins pass through holes in the plate and into the pinblock underneath. Tuning pins are about 2 1/2 inches long, and are made of steel. About an inch of the tuning pin is visible above the plate. The plate is about 1/4 to 3/8" thick. The other inch or so of the tuning pin is embedded in the pinblock. Pinblocks are usually made of hard rock maple or beech, and are usually laminated so that the end grain of the wood presses against the tuning pin from four or more directions.
When a piano's pinblock is originally made, at the factory, the holes for the tuning pins are drilled slightly undersize, a few thousandths of an inch smaller than the diameter of the tuning pins. When the tuning pins are driven into the holes, during stringing, a tight pressure fit results. After several decades, pinblocks get old or wear out. With the passing of time, the holes in the pinblock that hold the tuning pins become enlarged from repeated tunings or from the seasonal shrinking and swelling of the wood. As pinblocks age over several decades, the wood itself dries out and loses its resilience and the ability to grip the pins tightly. Sometimes the glue joints fail and the laminations of the pinblock begin to separate. When these things happen the pinblock will need to be replaced.
Pinblocks do not always have to be replaced. Frequently a pinblock can be reused, and oversize tuning pins installed. (The original tuning pins installed in pianos are usually size 1 or 2. You can go up to a size 7 pin. Each successive size is approximately .005" larger (in diameter) than the previous one.) A lot depends on the age and condition of the pinblock, and the piano.
The pinblock is a critical component of the piano. If it will no longer grip the tuning pins adequately it must be replaced. The making of a new pinblock is a complicated operation requiring meticulous fitting and cabinetry skills. These photos show the process we use for making new pinblocks for conventional grands such as Steinway, Chickering, Baldwin or Mason & Hamlin
The pinblock must be fit precisely to the plate. On the underside of the plate on most pianos is a lip or flange against which the pinblock must be securely seated. We mate the pinblock exactly with the flange so the tuning will be stable for another 40-70 years. When the strings are installed on the piano the pinblock presses against this flange. The flange supports the 20 to 30 tons of tension of all the strings combined.
To read more about the pinblock replacement process, click on the first photo in this section to see a larger version and then click next to scroll through the rest of the photos. At the bottom of each photo is a description of the process featured in the photograph.