Bottom rail, plinth / pedal rail
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The bottom rail (also known as plinth or pedal rail) is a fundamental structural element forming the base of the upright piano. It constitutes the lower part of the cabinet and provides overall stability to the instrument. This component is one of the piano's primary load-bearing elements and is assembled in the early stages of the construction process.
Structural Function and Assembly Sequence
The bottom rail plays a crucial role in the assembly sequence of the upright piano. During construction, it is glued simultaneously to the back panel of the instrument, together with the side panels, which are equipped with dowels to ensure accurate positioning. Once the back and the bottom rail are fixed, the piano can finally stand upright on its own—marking a significant milestone in the building process.
Structurally, the bottom rail must support and evenly distribute the considerable weight of the instrument, including the cast-iron frame, the action, the strings, and all cabinet components. Its design must also account for the dynamic stresses generated during musical performance and the immense static forces produced by string tension, which in modern pianos can amount to several tons of total load.
Materials and Construction Features
The construction of the bottom rail requires the use of particularly strong and stable woods. Traditionally, hard woods such as pearwood are used due to their ideal characteristics for this specific application. Pearwood is moderately hard, dense, solid, and medium-heavy, characterized by high resistance and elasticity. Flamed pearwood is even heavier, harder, and denser, although it may sometimes appear aesthetically neutral.
A typical feature of pearwood is the presence of small dark spots near the growth rings. When properly seasoned, pear becomes a very calm and dimensionally stable material—essential qualities for the construction of the bottom rail. This wood is widely used in the production of furniture and veneers, and in piano building, it is commonly employed for hammer shanks as well as for the bottom rail itself.
Other woods used include beech, oak, or maple, all selected for their mechanical properties and their ability to maintain dimensional stability over time. The cross-section must be appropriately dimensioned to withstand not only the static weight of the instrument but also the dynamic loads and tension fluctuations during use.
Support Systems
The bottom rail can be designed as a continuous single piece or divided into separate sections. The former provides greater structural stability but requires more precision during installation. The latter allows greater flexibility during assembly and makes partial replacement easier if needed.
Many modern bottom rails incorporate height-adjustment systems, typically achieved with leveling screws that compensate for uneven floors. These systems are particularly important for ensuring the stability of the instrument and the proper functioning of the action.
Integration with the Pedals
The bottom rail of upright pianos integrates the pedal system, which typically includes three pedals: soft pedal (una corda), sostenuto pedal, and damper pedal. The pedal housing must be precisely designed to ensure the correct operation and long-term durability of the transmission mechanism.
The pedal mechanism requires the bottom rail to provide solid anchor points for the levers and linkages, which must function accurately and silently over decades of use.
Dismantling and Technical Maintenance
During restoration or thorough maintenance, the bottom rail is removed following a specific sequence. After marking and disassembling the case parts, the technician proceeds by removing the action, the keyboard, the keyframe, the legs with their supports, and finally the bottom rail itself. It is essential to check for screws securing the legs and supports, often hidden beneath the wheels or bottom pads.
Some supports may have screws that penetrate the keybed, requiring special care during disassembly to avoid damage. The removal of the bottom rail must be performed cautiously, as this component is often glued and mechanically fixed to the main structure.
For less invasive interventions, such as pin replacement, complete removal of the bottom rail is not necessary: it is sufficient to tilt the piano onto its back using a tilting trolley, thus preserving the structural stability of the instrument.
