By Kate Redding, RPT
In our world of gadgets and machines, springs are hidden helpers. As such, go looking for them, and you soon realize springs are everywhere.
Instrument builders have long understood the utility of springs to store and release mechanical energy. In pianos, well-regulated springs are essential for playing with control and expression: for the action to repeat, to be reliable, to feel good.
With this in mind, it bears saying that when we work with springs, form follows function.
Elasticity and stiffness - the quintessential properties of springiness - are determined by material and shape. If you want to alter spring strength, you must change one or both. In reality, material stress will cause a spring to fatigue over time, so routinely observe and regulate springs when necessary.
Here's a run-down of four common spring types and where you'll find them in modern pianos.
These springs are squeezed from the ends toward the middle. Compression springs work best in vertical positions.
1. Grand Piano pedal Spring
An effective first line of repair is to remove the spring and clean the surface where it sits. Next, correct the friction on the pivot point of the moving part, which could be creaking. Threading a piece of bushing cloth through the spring will only dampen noise from the coil.
Use this method to avoid a damaged or fly-a-way compression spring:
2. Damper Tray Spring
Working with the damper tray spring (g) can be tricky when it's located behind the damper stop rail. The damper tray spring can cause problems if not seated correctly, but it's usually not the source of noise in the back action. In some pianos, the damper tray spring is a leaf spring screwed to the keybed. Read about leaf springs below.
3. Jack Spring
The jack spring (u) assists the jack’s return under the hammer butt. To replace a jack spring, clean the circular slot on the wippen with a special reamer. Use a dab of white glue on the bottom of the spring to fix it in place. The top of the spring is not glued to the jack.
Have you noticed that jack springs are tapered? A conical or barrel-shaped spring resists buckling under the rotation of the jack.
Since compression springs are designed to fit between parts, altering the length can have an unpredictable effect on spring strength. For a stronger spring, choose a thicker wire and/or a smaller coil diameter. For a weaker spring, decrease the wire thickness and/or increase the outside diameter of the coil.
The word "torsion" indicates a twisting motion. Wire thickness, the number of coils, and the distance between the spring arms determine the strength of these springs.
Many of the delicate regulating springs in pianos are torsion springs. They are secured through the coil with pins, thread, felt, and/or plastic bushings.
1. Grand Repetition Spring
The repetition spring (g) supports the repetition lever under the force of the hammer. When the hammer is in check, the spring arms compress. As the repetition spring recoils, it lifts the repetition lever and hammer shank high enough for the jack to return under the knuckle/ roller.
2. Sostenuto Tab Spring
Possibly the smallest torsion spring in the piano, and concealed to the point of near invisibility, the sostenuto tab spring (g) allows the tab to rebound after being deflected by the sostenuto rod.
3. Damper Spring
The damper spring (u) helps the damper make speedy contact with the strings. Regulate for peppy damper return.
4. Hammer Butt Spring
The hammer butt spring (u) helps the hammer return to its rest position.
Depending on their function, torsion springs can be graduated in thickness from bass to treble. For instance, the springs on wippens stamped with TREBLE are made with a finer wire gauge to support the smaller hammers in the top end.
Flat springs and cantilevers
In pianos, flat springs are relatively large compared to their compression spring and torsion spring counterparts. These springs help move an object, like the keyframe, a short distance. Look for them screwed on to cheek blocks, in the action cavity, and near the bottom door.
1. Action Shift Spring
This action shift spring has one spring arm, but some have two. It's harder to regulate but needs to be adjusted when too aggressive or too weak. Take care not to weaken the spring past the point of no return.
To regulate, secure the clamp it in a bench vise and compress the arm/s in the jaws of the vise.
2. Fallboard Spring
A fallboard spring (g) supports the fallboard in the open position. This one is screwed to the bass cheek block.
3. Sostenuto Spring
The sostenuto spring (g) applies downward pressure on the monkey to counteract the upward force