How the piano action works, what regulation adjusts, and common action problems in Singapore's humidity
The piano action is the most mechanically complex component of any acoustic piano — a system of over 5,000 moving parts that translates a key press into a precise hammer strike and immediate return. In Singapore's 70–90% relative humidity, the action's felt and leather bushings swell and contract continuously, gradually pushing every calibrated dimension out of specification. Piano regulation — the adjustment of all those dimensions — costs S$200–S$500 for upright pianos and S$400–S$700 for grand pianos. This guide explains how the action works, what regulation adjusts, and what specifically goes wrong in Singapore.
A piano key is a lever balanced on a centre pin (balance rail pin). When you press the front, the back rises. The key is guided vertically by a front rail pin. Both the balance and front rail pins are wrapped in woollen felt bushings that must be snug enough to control movement but free enough to allow easy travel. These felt bushings are Singapore's primary action problem — they swell in humidity and cause keys to stick.
The wippen sits on the back end of the key (or is mounted on the action rail in grand pianos). It is a small lever assembly that amplifies the key motion. When the key back rises, the wippen rises. On the wippen are two critical components: the jack and the repetition lever (grand pianos only).
The jack is a small angled lever on the wippen. As the wippen rises, the jack pushes the hammer butt upward, sending the hammer toward the string. Just before the hammer reaches the string, the jack tip contacts an adjustable regulating button and is forced to pivot out of contact with the hammer butt. This critical moment is called escapement — it allows the hammer to continue to the string under its own momentum and rebound freely, rather than being held against the string (which would damp the sound).
The distance from the string at which the jack escapes is called let-off or escapement. In a well-regulated upright, let-off is typically 1.5–3mm before the string. In a concert grand, it can be as close as 0.5mm for maximum control. Let-off that is too early means the hammer does not reach the string under jack power; too late and the hammer stays against the string (cipher).
Each note (above bass) has a damper — a felt block resting on the string. When you press a key, the damper lifts off the string, allowing it to vibrate. When you release the key, the damper drops back onto the string, stopping the sound. The sustain pedal lifts all dampers simultaneously. In Singapore, damper felt swells and can become "stiff" — imprecisely seating on strings and affecting sustain.
The grand action adds a repetition lever (also called the balancier or repetition spring mechanism) to each wippen. This allows a note to re-strike before the key fully returns to rest position — essential for fast passages and trills. The repetition lever catches the hammer on its rebound and holds it in a ready position, approximately one-third of the way back. Regulating the repetition lever is one of the more complex aspects of grand piano regulation.
Regulation is the process of adjusting every measurable dimension in the action to return it to specification. A full regulation typically takes 4–8 hours for an upright and 6–12 hours for a grand. Dimensions adjusted include:
| Regulation Point | What It Controls |
|---|---|
| Key height (dip) | How far the key travels before hitting the key frame |
| Key level | All keys at the same height when at rest |
| Hammer blow distance | Starting position of hammer relative to string |
| Let-off (escapement) | Distance from string where jack escapes |
| After-touch | Key travel after the hammer escapes |
| Damper timing | When damper lifts relative to key travel |
| Damper seating | How completely damper contacts string |
| Repetition lever height (grand) | Speed of key repetition possible |
| Repetition spring tension (grand) | Force of repetition return |
| Soft pedal travel (una corda, grand) | Hammer shift distance on soft pedal |
Singapore's most common action problem. Woollen key bushings swell in high humidity, gripping the guide pins. Keys go down but do not return. Repair: S$60–S$150.
A ciphering note is one that sounds continuously or sounds without the key being pressed. Most common cause: the let-off is set too close and the hammer stays against the string, or a swollen action part is pushing the jack into the hammer butt. Also caused by a broken or dislodged jack. Diagnosis needed: S$80 inspection will identify cause.
When felt and leather bushings absorb moisture, action friction increases across the board, making the piano feel heavy. Individual notes may feel noticeably different from each other — some heavy, some light — as bushing condition varies. Regulation and sometimes bushing replacement addresses this.
Keys that travel down but are slow to return (separate from sticking). Often caused by weak return springs or swollen action parts adding friction to the spring mechanism. On grand pianos, a weakened repetition spring causes the same symptom.
A key that goes down but produces no sound. Possible causes: broken hammer shank, broken string, jack disconnected from wippen, or a keybed issue. Each requires individual diagnosis.
General schedule for Singapore's climate:
All action problems diagnosed in one visit. Regulation quote included at no extra charge.
Sticky keys, regulation, ciphering, all action problems. Upright S$200–S$500. Grand S$400–S$700.