The first plastic piano action parts appeared in pianos built in the late 1940s, and because they were used only in smaller pianos, especially spinets, it can be inferred that the aim at that time was to save cost. However, these early plastic parts also appeared in console pianos made by the high-end Mason & Hamlin company, so there may have been other benefits to using plastic, such as uniformity and stability.
The first action parts made of plastic included the elbows (unique to spinet pianos), various action flanges, backchecks, and even damper levers. Unfortunately, all these early polyvinyl chloride (PVC) parts were doomed to failure because the plasticizers that kept the material pliable would gradually migrate out of the parts until they became brittle and prone to shatter, usually within five to fifteen years. As one who became a piano technician in the early 1970s, I was the grateful recipient of many plastic-elbow replacement jobs during my first several years in the business!
Plastics technology has come a long way since those early days. Kawai began using acrylonitrilebutadiene-styrene (ABS) for certain action parts in the late 1960s, and the material has proven extremely durable. According to Don Mannino, Kawai's director of technical training, "Kawai made the commitment early on to improve piano actions, both in terms of consistency of feel and reliability, and the early conservative application of ABS to upright action flanges has spread to upright hammer butts, wippens, and damper levers. In grands, the hammer flanges, wippen assemblies, and the entire damper underlever assembly is made from ABS." In the current Millennium III action found in Kawai's upper-level models, the ABS is reinforced with carbon fiber, making the parts stronger with less mass. The resulting action, according to Kawai, is more responsive to the player's intentions, including faster repetition. The use of plastic also allows Kawai to micro-engineer certain contact surfaces for ideal shape and texture, something that would be impossible with wooden parts.
Mason & Hamlin, through its WNG subsidiary, has thrust the use of nontraditional materials into high gear. Engineer Clark makes a strong case for pursuing better parts by using nontraditional materials. "When you go to a new material, if you don't take advantage of its properties, there's no point in using it. In our case, the material (a composite of nylon and glass) is 10 times stronger than maple, but weighs only twice as much." By radically redesigning the wippen assembly to remove and redistribute mass, Clark is left with a part that looks like miniature bridge trusses; while still slightly heavier than a comparable maple part, it is many times stronger. "To reduce inertia, we've shifted the center of gravity closer to the center of rotation," he says. "It's not reasonable to do that with wood." Other advantages to using a modern composite in place of wood are that the composite is more consistent in both weight and strength, and is completely impervious to changes in moisture and temperature.
According to Mason & Hamlin co-owner Mark Burgett, the hammer shanks in the WNG action are essentially carbon-fiber tubes, which he says are not only stronger than traditional maple shanks, but also more consistent in flex strength. This consistency pays off in making the piano's voicing more consistent. "Much of what we have to do to the hammers to make the voicing more even is made necessary by inconsistency in the wooden hammer shanks," Burgett says. "If one shank is more pliable than another, the tone of that note will be darker and may include an unwanted noise element. With the carbon-fiber shanks, we find that much less hammer voicing is needed." Since January 2010, all Mason & Hamlin grand pianos have been equipped with all-composite top actions. All-composite grand damper actions are now available, and the company says that a composite vertical piano action is in the works. All of the WNG parts are also available to piano rebuilders.