Piano (How Products are Made)
The piano may be the best known and loved of all musical instruments. It also has the broadest range of any instrument, so music for all other instruments can be composed on it. It can be played solo, but most other instruments, including the voice, use the piano for accompaniment. Technically, the piano may also be the most complicated musical instrument with over 2,500 parts.
The piano is a stringed instrument. Its many parts are organized into five general structural and mechanical areas of either grand or vertical pianos. These are: the case of the wing-shaped grand piano (or the cabinet of the vertical or upright piano); the soundboard and the ribs and bridges that are its components; the cast iron plate; the strings; and, collectively, the keys, hammers, and piano action or mechanism. The case has many structural parts for attaching legs and tuning pins, but perhaps the rim and the keybed or shelf where the keys and piano action will be installed are most important. The soundboard amplifies the vibrations of the strings, which are transmitted through bridges.
The cast iron plate is installed over the soundboard and pinblock (part of the case), and it provides the strength to anchor the strings under tension. Nose bolts and perimeter bolts anchor the plate to the braces and inner rim of the case. The 220 to 240 strings of the piano are attached to hitch pins along the curved edge of the cast iron plate and to tuning pins across the front of the piano, roughly parallel to the keyboard. The piano action is still more complicated and includes the keys, hammers, and mechanism or action.
Names for pianos usually indicate their sizes. Grand (wing-shaped) pianos range in length from 4 ft 7 in-9 ft 6 in (1.4-2.9 m) from the front of the keyboard to end of the bend. The "baby" grand is 5 ft-S ft 2 in (1.52-1.57 m) in length; smaller grand pianos are called "apartment size." The larger sizes are the medium grand and concert grand. Modern vertical piano design has changed little since 1935. Verticals range in height from 36-52 in (91-132 cm) with small variations in width and depth. The five standard sizes from smallest to tallest are the spinet, consolette, console, studio, and professional pianos. Pianos are frequently chosen for appearance, and cabinets are available in most furniture styles and finishes.
The piano's ancestors are the first stringed instruments. Plucking, striking, and bowing of strings was known among all ancient civilizations; the harp is mentioned in the Book of Genesis in the Bible. The psaltery was an ancient box-type instrument with strings that were plucked with a pick. Keys were added to stringed instruments to make the family of instruments led by the harpsichord, but keys are used to pluck strings in the harpsichord, the most popular instrument of the seventeenth century. A parallel development was the dulcimer, another stringed box with strings that are struck. Keys and strings were paired in a striking instrument in the clavichord, which led directly to the invention of the pianoforte or fortepiano.
Bartolomeo de Francesco Cristofori made harpsichords in Padua, Italy. He is credited with having invented the piano in 1700. Cristofori's piano had hammers that struck the strings by falling by momentum, after having been moved by the action parts linking the hammers to the keys. The hammers were caught by back checks or hammer checks to keep them from bouncing up and down on the strings after the initial strike. This method allowed the strings to continue to vibrate and make sound and for them to be struck loudly or softly, unlike the harpsichord. Johann Andreas Silbermann of Strasbourg, France, continued Cristofori's interest in the pianoforte, and the instrument became popular in Germany after Frederick the Great purchased several. Johann Sebastian Bach approved of it in 1747.
The piano had replaced the harpsichord in importance by the end of the eighteenth century. Cabinetmakers built beautiful cases for them. The square piano was built mid-century, and more musicians began writing music specific to the piano, rather than borrowing harpsichord tunes. Piano building began in America in 1775, and changes to the design of the hammers and to the playing mechanism or action improved the sound and responsiveness of the instrument. Jean Henri Pape of Paris patented 137 improvements for the piano during his life (1789-1875). In England, John Broadwood developed machines to manufacture pianos and reduce their cost.
Improvements continued from 1825 to 1851 with over 1,000 patents in Europe and the United States for stronger, more deft pianos with greater control and repetitive motion. By the mid-nineteenth century, the modern piano had emerged based on the development of the cast iron plate for structural strength and cross-stringing by fanning bass strings over trebles. By 1870, Steinway & Sons had developed this fanning method called the over-strung scale, so that the strings crossed most closely in the center of the soundboard where the best sound is produced.
C. F. Theodore Steinway also developed the continuous bent rim for the case, which enhanced sound transmission by using the acoustic properties of long wood fibers. These improvements were adapted to all styles of pianos including grand, upright, and square pianos. By 1911, there were 301 piano builders in the United States. Production peaked in the 1920s and declined greatly because of the Great Depression in the 1930s. Today, there are approximately 15 piano manufacturers in the United States, and Japan is the world's largest producer of pianos.
The design of the piano has not changed appreciably since the late 1800s, although manufacturers may use different materials or approaches to the manufacturing process. The manufacturing process for the grand piano is described below; there are some differences in manufacturing the vertical or upright piano and in operation methods, particularly the angle at which the hammers strike the strings.
Pianos are made of the finest materials, not only for appearances but for excellent sound production. The long fibers of maple wood are strong and supple for construction of the rim, but long fibers of spruce are needed for the strength of the braces. Wood is also needed for making patterns of other parts. Metal is used for a variety of parts, including the cast iron plate. Sand is needed for casting molds. The character of the sand is modified by using additives and binders such as bentonite (a type of clay) and coal dust. Molten iron for the casting is made of pig iron with some steel and scrap iron to add strength. Strings are made of high tensile steel wire that is manufactured at specialized piano string mills.
Pianos are designed by specially trained and educated engineers called scale engineers. Scale engineers choose the materials, create the designs and specifications, and develop the interactions of the parts of the piano. Perhaps the most important aspect of design relates to the structural strength of the piano. About 160-200 lb per sq in (11.2-14 kg per sq cm) of tension is exerted on each of the 220 or more strings in the piano. The piano must perform well, but it also must remain stable over time as changing conditions affect the many materials in the piano differently.
The cast iron plate must support the tension of the stringing scale, covering the sound-board very little; it must have maximum mass for strength, but minimum mass for sound quality. Its shape is unique to the design of the piano because it conforms to the string layout, the placement of the bridges on the soundboard, and the paths of the strings. Because the material is brittle, it must be supported in places where the strings apply tension. Holes are designed in the curved side to prevent the plate from cracking due to thermal stress after it is poured and cooled, and this design allows sound to rise from the soundboard too. The scale engineer first sketches a proposed plate, draws it to scale, and makes a wood pattern; this design is later used for manufacture.
The Manufacturing Process
Bending the rim of the case
- 1 Steinway's method of rim bending is still used and is the first step in assembling the grand piano. Layers of long-fiber maple wood are glued together and bent in a metal press to form a continuous rim; both the inner and outer rim are made this way. Up to 22 layers form each piano rim, and the layers may be up to 25 ft (7.62 m) long. Resin glue is applied by machine, then the layers are carried to the press where they are shaped. The rims are stored in braces to keep them from changing shape. They are seasoned in controlled temperature and humidity conditions until the wood meets a specific moisture content where it will hold its contour. The bent inner rim is then fitted with other wood components, including the cross block, the pinblock, the cross braces, the keybed, and the backbottom. These are glued and doweled in place.
- 2 The cabinet is finished to improve sound properties as well as for appearance. The cabinet is sanded so stain is absorbed properly, wood is bleached to equalize appearance of the veneer, prestaining and staining are done next, wood fillers (sometimes with a washcoat) are added, and a first coat of sealer or lacquer is applied. The surface is sanded again, special glazes (for antiquing or other effects) are added followed by two more coats of lacquer, sanding is done again, special trims are added, and two final coats of lacquer are used. The cabinet is dried for up to 21 days before it is hand-rubbed to its final finish.
Making the structural components
- 3 The wood components of the piano (collectively called the framework)he pinblock and the cast iron platere the parts of the piano that support the tension of the strings. Braces are made of select spruce, and the pinblock or wrestplank is constructed of bonded layers of rock maple. The pinblock is quarter-sawn or rotary cut to maximize the grain structure's grip on the tuning pins. The laminated layers are also glued at different angles to each other so that the pins are surrounded with end grain wood. The pinblock has one hole per string, or up to 240 holes, drilled in it.
- 4 The cast iron plate is made in a piano plate foundry. Match-plates are made of metal from the wood pattern designed by the engineer with top and bottom pieces to match. Sand molds are made from the match-plates, and these are used to cast the plate. Molten iron is poured through the molds and allowed to harden during the founding process (a controlled cooling process) to produce a plate weighing about 600 lb (272.4 kg). After the plate is cooled and removed from the molds, sand is blasted off the plate with steel grit. The plate is transported on overhead conveyors to a drill room where holes are drilled for the tuning pins, nosebolts, bolts to the frame, and hitch pins. The hitch pins are inserted next; then the casting imperfections are removed from the plate by grinding and drilling. Oils are also removed. The plate is hand-sanded and rubbed, primed, and painted.
- 5 The cast iron plate is suspended above its piano during the process of fitting. The plate will be lowered and raised in and out of the piano several times as the pinblock, seal against the rim, and the sound-board and bridges are fitted.
Creating the soundboard
- 6 The soundboard is a thin panel of spruce that underlies the strings and the cast iron plate and rests on the rim braces. Its parts are the board itself, supporting ribs on the underside of the board, and the two bridges over which the strings are stretched. The soundboard is made of spruce that is 0.25-0.375 in (0.635-0.95 cm) thick; it acts as a natural resonator, is strong for its weight, and can be vibrated by the strings because of its lightness. Spruce is air dried then kiln dried to a specific moisture content. It is then cut into strips that are 2-5 in (5.08-12.7 cm) wide, the edges are glued, and the strips are pressed together and dried. A pattern is superimposed, and the soundboard is trimmed to grand piano size.
- 7 The soundboard is curved to produce the right sound. The curve is called a crown that arches upward toward the strings. The arch is made by fitting ribs of lightweight spruce or sugar pine wood to the underside of the board. The ribs are carefully cut from patterns, then fitted and glued to the sound-board using a rib press that accurately positions the ribs, then forces the board into the proper curvature. The ribs are cut along the wood's lengthwise grain and fitted at right angles to the lengthwise grain of the sound-board, so that vibrations are evenly transmitted. The ends of the ribs are feathered, then fitted into notches in the framework of the piano that will exactly support the arch of the crown; the pianomakers use special patterns to guide these cuts in the frame.
- 8 The two soundboard bridges transfer the vibrations of the strings along their lengths to the soundboard. The long bridge is crossed by treble strings, and the bass strings that fan across the trebles cross the short bridge. The bridges are complicated because they must parallel the grain of the soundboard closely, curve with the crown, and support the strings, which exert a down-bearing pressure on the bridges and therefore on the soundboard. This pressure must be supported by the strength of the bridges and the arch of the crown, or the tone of the strings will drop. The bridges are made of solid blocks of wood or of laminated wood. Hard maple is used in American-made pianos, and falcon wood (beech) is used in Europe. Laminated bridges must be placed with laminations perpendicular to the soundboard or the glue layers have a damping effect. The bridges are glued to the soundboard and also fastened to it with wood screws capped by soundboard buttons made of wood that act like washers and keep the screws from grinding into the board. The bridges are notched on both
Stringing and tuning
- 9 Piano string is made in specialized mills and consists of carbon steel wire. The bass strings are also wrapped with copper windings in a process called loading the strings. The windings add weight and thickness to the steel core strings so they vibrate more slowly and can be made to lengths that fit a piano of practical size; without loading, bass strings would have to be 30 ft (9.14 m) long to produce their sounds. Treble strings are short, are not wound with copper, but are grouped in threes to make one tone. Scale sticks are used as standards for each string, acting as a gauge of each kind of wire and determining how many sizes of string are needed; up to 17 different diameters of wire may be used to string one piano. Piano strings require special care and handling because they lie straight after they are formed, cut, and loaded and are never wound on rolls. After the strings are strung, they are held in place near the tuning pins by metal bars and special brass studs called agraffes. Other bars position the strings properly near the hitch pins.
- 10 Tuning pins are made from steel wire. The wire is cut to the proper length, the ends are shaped with a die, and the pins are loaded in a tumbler where rough edges are smoothed away. The tumbler empties them into a press where swags that fit tuning hammers are formed at the tops of the pins. Holes for the strings are drilled into the swagged ends of the pins, the pins are cleaned of metal chips and oil, and nickel-plating is applied to the pins to keep them from rusting. The pins are threaded to turn easily during tuning, then they are subjected to controlled heating called blueing, which oxidizes the outer surface of the threads of the pins (where the nickel plating was removed during threading) so the pins will grip the wood in the pinblock. Special machines insert several pins at a time through the holes in the cast iron plate and into the pinblock where they are fitted in place by hand.
Constructing the keyboard and action
- 11 Keyboards, key and action frames, and actions are made by specialty manufacturers. The keys balance and pivot on a set of either two or three rails that are covered with felt to prevent noise. Guide pins for each key are inserted in the front or head rail and the middle or balance rail. The keys themselves are made of lightweight wood that is cut to size and dried in kilns. The keys are covered with black or white plastic, although in the past ivory and ebony were used. The plastic key covers are molded to cover a group of keys that are later cut individually. Holes are drilled on the undersides to fit the guide pins. Capstan screws are mounted on the back edges of the keyboard extending inside the piano; the action will be seated on these. The keys are now cut into 88 individuals, which are sanded and polished on the sides. The black keys are also stained black before the black caps are glued on. The keys are rematched to the keyframe, punchings resembling washers are placed over the guide pins, and the keys are placed on them.
- 12 The voice of the piano depends on the quality of the hammers. Many materials from elkskin to rubber have been used over the history of the piano, but today, hammers are covered with premium wool felt of precision-graduated density. The felt is made by specialists who begin with select wool that is carded, combed, folded, and compressed into felt in tapered strips. The thinnest felt is used for the treble hammers, while thick felt is used for the bass. The core of each hammerhead is a wood molding, and an underfelt and top felt are bonded in place with resin to cover the molding. The hammerheads are made in long strips of the same size then sliced into individual hammerheads by hand or automation. The complete set of hammers is installed in the piano. The sound of the piano is adjusted by a specially trained tuner called a voicer. The key actions must respond with the same resistance. The felt hammers are modified with a sticker or needler that retextures the hammerheads and changes the sound.
- 13 The final parts are added, including the pedals and their trapwork, the fall-board or key cover, the music rack, the hinges and top lid, the topstick that supports the raised lid, and many other details. All parts are carefully made so they fit tightly and do not rattle or otherwise affect the sound of the instrument.
Pianos would not exist without quality control in all aspects of production because the instruments are too sensitive and dependent on the interaction of many parts and materials. For example, quality begins with the scale engineer's design. Metallurgists check the metal content of the iron plate; chemical analyses are made of the other contents, including carbon, sulfur, phosphorus, and manganese. Temperature is also critical; the molten iron is 2,750°F (1,510°C), and founding or hardening temperatures are also carefully monitored. String is similarly controlled and tested during manufacture for elasticity, resiliency, and tensile strength.
The process of piano manufacturing has remained essentially the same for a century, but scale engineers are always seeking new methods. Vacuum casting has recently been used to produce cast iron plates with smooth finishes requiring no grinding.
Where to Learn More
Ardley, Neil. Music: An Illustrated Encyclopedia. Facts On File., Inc., 1986.
Bielefeldt, Catherine C.; Weil, Alfred R., ed. The Wonders of the Piano: The Anatomy of the Instrument. Belwin-Mills Publishing Corp., 1984.
Dolge, Alfred. Pianos and their Makers: A Comprehensive History of the Development of the Piano. Dover Publications, Inc., 1972.
Ehrlich, Cyril. The Piano: A History. Clarendon Press, 1990.
Ford, Charles, ed. Making Musical Instruments: Strings and Keyboard. Pantheon Books, 1979.
i>Gillian S. Holmes