THE CAST IRON FRAME
The metal frame, of a piano is usually made from cast iron. It is crucial for the plate to be very robust. As mentioned previously, the average upright or medium-sized grand piano’s strings have a combined pull of about 18 tons, and the tension in a 9 foot concert grand is close to 30 tons!
Cast iron is easy to cast and machine, has flexibility sufficient for piano use, is much more resistant to deformation than steel, and is especially tolerant of compression. Including an extremely large piece of metal in a piano is potentially an aesthetic handicap. Piano makers overcome this by polishing, painting, and decorating the frame, often including their ornamental medallion.
PIANO ACTIONS – PARTS & MATERIALS
The numerous parts of a piano action are generally hardwood,such as maple,beech, or hornbeam, but since World War II, makers have used some plastics.Early plastics were incorporated into some pianos in the late 1940s and 1950s, but proved disastrous because they crystallized and lost their strength after only a few decades of use. More recently, Kawai built pianos with action parts made of more modern materials, such as carbon fiber reinforced plastic. These have, so far, performed reasonably, but it may take decades to know if they can match the longevity of wood.
The heart of the grand piano is the soundboard. The sound of a string vibrating on its own is very weak. A good example of this type of sound is to listen to a solid body guitar when it is not plugged in to an amplifier – almost inaudible ! In a piano, it is amplified by this large, thin wooden diaphragm glued into the outer case around its perimeter. The soundboard is usually made from Sitka spruce, planed to about 3/8″ thick and glued together along the side grain, and has ribs on the under side, with the bridge on the upper. Spruce provides a high ratio of strength to weight.
The best piano makers use quarter-sawn, defect-free spruce of close annular grain, and make sure that it has been carefully dried over a long period of time before they make it into soundboards. Many pre WW 2 light aircraft such as the products of the Bellanca Aircraft Company were constructed using spruce for spars and ribs in their wings. Aircraft grade spruce is still being used for the kit aircraft market to this day. This wood has just the right balance of stiffness and flexibility to effectively transmit sound. The soundboard is bowed slightly upward towards the strings which helps it to maintain compression, and keeps it from caving in under the pressure from the strings. Cheap pianos often have plywood soundboards, which produce an inferior sound..
In the early years of piano construction, keys were commonly made from sugar pine. Today they are likely to be made of spruce or basswood. Spruce is normally used in high-quality pianos. The black keys were traditionally made from ebony and the white keys were covered with strips of ivory, but since ivory-yielding species – elephants – are now, thankfully, endangered and protected by treaty, plastics are now almost exclusively used. Also, ivory tends to chip more easily than plastic. Legal ivory can still be obtained in limited quantities. The Yamaha Piano Company invented a plastic called “Ivorite” that they claim mimics the look and feel of ivory; it has since been imitated by other makers.
Strings pass over wooden bridges- a long curved one for the treble and a
shorter one for the bass strings- which transmit vibrations of the strings to the soundboard. Steel bridge pins are driven into the bridges to keep the strings in place, to aid in sound transmission and to cleanly terminate the vibrating portion of the string (much like a guitar player’s finger would press down on the fretboard). The other end of the string terminates at the plate near the tuning pins. Bridges must be well constructed, both to transmit sound properly and to avoid splitting under the hundreds of pounds of downward pressure exerted by the strings. Most bridges are made of maple or beech, either solid or laminated, sometimes with a top layer, or cap of more durable material.
I hope you have enjoyed reading this series of Nuts and Bolts of Grand Pianos. As you have probably gathered, I am very passionate about all things to do with Grand Pianos, especially playing really nice examples of them. The piano in this photograph on the left is a Kawai hand finished grand of 2 metres length. Beautiful !
Please enjoy this video about making a Steinway