Wood quality and types used in piano manufacturing
One of the many factors in evaluating a piano and a primary one at that is the quality of the wood in which it is built. Many different types of wood are used in a piano for various parts. These include birch, maple, fir, oak, mahogany, ebony, spruce and many other exotic woods. Logs are harvested and usually sawed into planks at the sawmill to be used in various piano parts or it is soaked in hot water to soften, and then peeled by a machine to produce veneer for the exterior case.
Once the wood is selected it is put through a drying process. The wood is air dried from 6 months to two years depending on the parts in which they are to be used. If the wood is not dried properly it can lead to warping and cracking. Wood that is air dried to 12-14% then kiln dried to 11% is a normal drying percent for piano soundboards however, some piano soundboards destined for the U.S. are dried to 7% to factor for possible arid conditions in this country. After the kiln drying, the wood is seasoned again before the parts are made and is usually stored indoors. Old world violin makers used to look for wood that had been dried over 100 years however, technical advances and kiln drying have eliminated the need to dry lumber this long.
The specialized job to select lumber that is usable for a piano is very important as the percentage that can be used in piano manufacturing is small. In a high quality piano, about eleven percent of the lumber is of high enough standard for well built piano manufacturing. Selecting this wood takes skill and a trained eye. Selected wood will be straight grained, closed and without knots. After the wood is selected and separated for its particular part usage it can be readied for gluing. Glues used in piano manufacturing are highly resistant to heat and humidity changes. Once selected, the wood is prepared for its many different part constructions.
One part in particular is the sound board. Normally spruce is used as it has highly elasticity and is the most reverberant. Different manufactures use different types of spruce (Sitka, Yezo, European, Adirondack, and Canadian just to name a few). The spruce is usually harvested when the sap is at its lowest content. Ideally the spruce boards should have a grain with about 10 annual growth rings per inch. Soundboards are made to curve and have a crown very much like a speaker cone. Expert craftsmanship is essential if the crown is to hold up for many years of use and possible environmental changes. Poor quality sound boards will straighten over time and loose the robust tonal quality they once had. The spruce planks of a sound board are glued together and then held in place by wood strips called ribs. The grain of the rib runs at right angles to the grain of the sounding board. These ribs help to distribute resonance and reinforce the board. Some piano makers curve the ribs to support the crown within the sound board. Once the board and ribs are together they are ready for the bridges.
Maple is usually the desired wood for the bridges. The bridge transfers the vibrating strings energy to the soundboard and is usually placed near the crown of the soundboard. Bridges are typically glued to the soundboard but in high quality pianos the bridges also have a dowel joint through the bridge, board and rib to transmit the string vibrations even more efficiently.
Maple is also used for the pinblock and is laminated to add strength. Other woods used in pin blocks are beech. These hardwoods ensure a high degree of tuning stability over a long period of time.
Keys and Action Mechanism
The keys of the piano are sometimes made of fir. It is tough and resilient to heavy wear. Usually cut from a single piece of wood all 88 keys are seasoned further to allow moisture to escape and prevent warping. Once the key stick is ready the keytops (white and black) can be attached. Materials for the white key tops are usually a synthetic ivory or plastic resin and for the blacks it is wood (sometimes ebony) or a special resin type material.
The action mechanism is made of many components and precision is the key. For the best quality pianos these action parts should be made with minute margins of less than a thousandth of an inch in part production. Usually maple is the choice for action parts although depending on the manufacture other types of wood are also used. These parts are made to withstand constant friction and have to be very durable. The action is the heart of the piano and what determines the touch to be light or heavy.
Case and Rim
The case, rim, back posts and exterior of the piano are made of many different woods. The rim is usually made from maple and/or maple and mahogany laminate but sometimes the rim is made of spruce by a particular manufacture of high quality European pianos. The back posts are made from spruce. The exterior case and cabinet of some pianos are made of a solid plywood core. (Poplar and birch are commonly used.) This core is covered with layered veneer with grain running at right angles to each other for less warping potential. The outer veneer layer can be walnut, mahogany, maple, cherry, oak, rosewood and many other exotic woods for the furniture aspect of the pianos finish.
There is no substitute for quality wood in piano manufacturing. Wood is very special as it lives and breathes and its selection requires expertise at the highest level to produce the best quality pianos and their associated parts.