T e two rims act as a suspension system to keep pressure off the drum’s shell and head. Aluminum die castings are preferred because they are consistent, light- weight, cost eff ective and machinable. T e diecast- ing operation can produce perfectly round rims with a relatively small amount of labor. T e castings also hold up to the demanding physical stress that comes with being a part of the percussion section. T e overall sound of
The grand piano puts thousands of pounds of pressure on its cast iron frame.
drums are improved by the casting process, because roll-formed rims require welds to correct imperfections, which can lead to stretching and less than ideal performance.
Grand Pianos Since the mid-19th century, metal
castings have been an integral part of grand pianos. Until this development, patented in 1825 but not commonly used until decades later, piano frames lacked the necessary strength to resist the strain of the strings, which led to ever-rising pitch. Cast iron’s high compressive
strength withstands the inward pres- sure created by the piano’s strings, improving tone and consistency. T e plate, which can weigh up to 400 lbs., begins just behind the keyboard and stretches to the rear of the piano. T e strings of the instrument originate at a tuning pin, which appears to be attached to the cast metal plate. In fact, the pin extends through the plate and only makes contact with the large oak casing, the piano’s other major structural feature. T e casting and wooden casing together support between 25,000 and 35,000 lbs. of pressure, corralling the strings between the tuning and hitch pins at the rear. While the large sand casting sounds simple enough, calling it a plate belies the intricacy that goes into the engi- neered component. “In terms of size and complexity, the plate has some very interesting
32 | MODERN CASTING December 2014
challenges from a casting stand- point,” according to Bob Berger, director of customer satisfaction, Steinway and Sons, Long Island City, N.Y. “With a relatively imbalanced shape, it has a tendency to move during cooling.” T at imbalance stems in part from the intricate passageways that must be cast into the rear of the plate, where strings of diff er- ent pitches pass under, over and around each other. T e plates also are designed with sev- eral cast-in holes that
lighten the massive pieces of metal and also contribute to the acoustic signature of the instrument. T e metalcasting process used to
produce the plates in pianos remains traditional, from the development of patterns to pouring in sand molds, but each is unique to the model of piano that it is made for.
Handbells
Handbells are most often asso- ciated with religious services and church choirs, but the melodic noisemakers rely on a recognizable casting to produce their musical brilliance. Because of the exact- ing specifications of the metal that is used in the production of instrument-quality bells, the process has changed very little over time. Bells feature a special
bronze alloy of 80% cop- per and 20% tin (with trace amounts of contaminants). T e tin produces the bell’s beautiful sounds but it also makes it extremely hard and brittle (take the Liberty Bell, for example). Several casting pro- cesses have been tested for their ability to improve the grain structure and subsequent sound quality of bells, but sand casting is the preferred process. Finishing bells remains tedious and manual, and scrap is common considering
the instrument’s necessary fine grain structure for acoustic resonance. Bells are cast with excess metal on the inner surface, which will be struck by the clapper. To tune them, trained acousticians machine away layers of metal, judging by ear when the bell produces the desired sound. Unfor- tunately, in the course of this process, subsurface defects can be found. But the cost of metalcasting scrap is mini- mal enough to avoid the need for non- destructive testing prior to machining. T e inner surface of a concert bell
is machined to a pitch about 40% higher than the desired note. T is gives the bell maker a bit of leeway when the outer surface undergoes multiple rounds of sanding.
Woodwind Components
Clarinets and fl utes have intricately designed sets of keys and rods that allow musicians to hit all the neces- sary notes. T e fl ute, for instance, requires some 120 diff erent compo- nents to produce a fi nal set of 20 keys. While these can be stamped or forged, the highest quality keys are invest- ment cast in alloys containing nickel, brass, silver and/or gold. T e process begins with the injec-
tion of hot wax into a plaster mold of the particular cast component. Multiple molds are arranged in a clustered tree and dipped into a plaster- or ceramic-based material. After the plaster has set, the wax is burned out leaving a hollow cavity into which the metal is poured. After cooling, the ceramic
is removed and discarded. T e cast components are broken off the tree and machined and polished. Some are plated with other alloys
Handbells rely on the sand casting process to meet strict specifi cations.
before fi nal installation on the instrument. Similar to the invest-
ment casting process, many saxophone keys are diecast, which uses a
steel die in place of the ceramic mold. Diecast keys and components have improved strength and feel compared to stamped keys, with price often dictating the method of production.
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