Understanding Piano Action Mechanics
The piano action is the mechanical heart of the piano, comprising over 10,000 parts in grand pianos and slightly fewer in uprights. It transfers the motion of pressing a key to the hammer striking the strings. A well-functioning action is crucial for precise control over dynamics, timbre, and articulation.
Before You Begin: Tools and Preparation
Essential tools for rebuilding a piano action include:
- Screwdrivers
- Pliers
- A spring hook
- A regulating rack (grand) or spoon bender (upright)
- Key lead weights
- Needle-nose pliers
- Contact adhesive and hot glue
Disassembling the Action
Begin by carefully removing the piano action from the instrument. In an upright, open the top lid and front panel. In a grand, lift out the action after opening the lid and music desk.
- Remove the Keys: Label each key to ensure they return to their correct position. Unscrew the brackets holding the keys and gently lift them out. Store them in a safe place.
- Dismantle the Wippens: Disconnect the wippens (the assembly pivoting when a key is pressed) from each key. They often just snap off or may be screwed in depending on your piano model.
Servicing the Keys
Each key should be checked for balance and ease of movement. Remove old felt bushings using a small tool and replace them if compressed or worn. Re-weight the keys if necessary by adding or removing lead weights to ensure even touch across the keyboard.
Rebuilding the Wippens
Replace worn springs and felts. Check the jack and repetitions for damage or excessive wear. Adjust or replace the flanges (pivot points) if they bind or have excessive lateral movement.
Hammers and Dampers
- Replace Hammer Felts: If the hammers are too deeply grooved or hardened, consider replacing the hammer felt or reshaping the hammers. Use specialized tools to soften or harden the felt to match the desired tone.
- Attend to Dampers: Replace worn damper felts. Ensure that each damper lifts off the string cleanly when the corresponding key is pressed and returns snugly without buzz.
Regulating and Adjusting
Regulating is essential for simultaneous action of the piano parts to result in an even, responsive feel across the keyboard.
- Set the Let-off and Drop: Adjust the let-off (the point where the hammer disengages from the jack and flies freely at the string) and the drop (the distance the hammer falls back after flying towards the string but not striking it) for each key.
- Align Backchecks: Ensure the backchecks catch the hammer at the proper distance and angle to prevent the hammers from bouncing back to the strings.
- Regulate the Key Dip: Adjust the depth each key goes down when pressed. Consistency here ensures even dynamic performance.
- Adjust the Repetition Springs: These control how quickly a key returns to its rest position after being pressed.
Final Checks and Testing
Reinstall the action into the piano and conduct a thorough test playing every key in multiple dynamic ranges. Listen for any abnormal sound and check the responsiveness of the action. It may take several small adjustments to achieve the desired feel and sound.
Voicing the Hammers
Lastly, voicing the hammers is vital for tone control. Using a voicing tool, adjust the density of the hammer felt by pricking it to soften or harden the sound. This customizes the piano sound to the musician’s preference.
Rebuilding a piano action demands precision and patience, but revitalizing an aged instrument can be profoundly satisfying. A fully regulated, well-voiced piano can offer a dramatic improvement in performance, ensuring that both pianists and audiences enjoy the richest musical experience.
