Music History quiz: What is the single most notable feature in a modern grand action? If we answer “double escapement”, then as piano historians we can high five. But as piano technicians we may be quietly confused. In our training, did we learn how to analyze, trouble-shoot, or regulate double escapement? Well we did, if by double escapement we mean letoff and drop!
But the significant contribution of double escapement was not about escapement or drop. It was about helping a spring-loaded lever enhance repetition. And although the repetition lever does need escapement and may be adjusted by the symptom drop, what else should we know? If we expand the term to “simultaneous double escapement”, a timing choice emerges between letoff and drop that I call segue.
For a note’s hammer to create a musical tone, it needs to fly freely into strike and bounce back unobstructed. In Escapement #1, letoff button pulls jack from under knuckle. In Escapement #2, dropscrew holds repetition lever out of the way. Together, the two escapements disconnect finger, key, and whippen from knuckle, shank, and hammer.
In terms of roles in a grand regulation, both Escapement #1 and Escapement #2 function as Disconnectors. But each also serves as Accessory to the Reconnector (repetition lever) by strategically increasing spring tension during disconnection.
Before Erard’s patent in 1821, pianos played with just the first escapement. Hammers and jacks had to return to rest to reset. His spring-supported repetition lever solved the delayed reset problem but created a collateral need for Escapement #2 – the repetition lever, as well as the jack, must be out of the way when the hammer strikes.
For maximum power and control, jack pushes against knuckle for as long as possible before being yanked out of the way. If the jack kept going, finger, key, jack, shank, and hammer would uncomfortably collide with unison strings, jamming, making noise, and inelegantly muffling the result. If the jack was just stopped, close enough to the strings to maximize power and control but not pulled out of the way, another kind of collision would occur, causing player discomfort, multiple strikes, and spoiled repetition. Letoff (Escapement #1) must not just disconnect jack from knuckle. It must also remove the jack from an otherwise inevitable collision as the knuckle returns.
Without a repetition lever, the knuckle-shank-hammer’s bounce after strike far outstrips the whippen’s return by gravity, trapping jack behind knuckle until a bumping on the rest cushion sets it free. And without its own spring-loading, the jack would stay trapped, in spite of the bump.
At rest and during stroke, rep lever offers jack spring-supported assistance, smoothing both initiation of stroke and subsequent sliding of jack on knuckle. During double escapement, both jack spring and repetition spring are being cocked for the coordinated effort of getting jack back under knuckle as early as possible. After strike, rep lever’s spring-sprung pressure on knuckle reengages, further strengthening (for both rep lever and jack if a butterfly spring) as it goes into check. Then, when finger lifts, key retreats, and backcheck releases, the repetition spring pushes whippen and key ahead of the returning shank and the spring-sprung jack has its opportunity to pop back under. With no backcheck engagement, the returning shank directly drives whippen and key ahead of itself with similar affect. In either version, the opening whippen levers key down from shank during their return, enough for jack to reset well before reaching rest position.
The term “drop” adds confusion, because it refers not to stopping the repetition lever (escapement), but to a symptom used to adjust it. By playing a hammer super slowly through letoff and holding back as jack clears knuckle (something never done in actual playing), we can observe the hammer drop (knuckle falls from jack to rep lever). But what we are really trying to regulate is where the rep lever disengages and reengages: we turn drop screw down to stop rep lever sooner and up to stop it later. But how do we decide on, observe, and regulate the timing of Escapement #2?
There are three possibilities for timing, and each depends on first setting letoff. One, the jack trips first and the rep lever continues bearing upward on the knuckle. This might reduce knuckle-jack sliding friction but we’re trying to get letoff as close to the strings as possible. If the rep lever carries on after the carefully set first escapement, its hammer might violate the string excursion boundary of a previously struck note, causing a "zing" or worse.
A second possibility stops the rep lever before the jack starts to let off. Here, with the rep lever support withdrawn, the jack starts into its escapement bearing full hammer weight and associated friction. In both cases, the player may detect two bumps and feel the spring of one engage before the other. This all happens at nearly the end of stroke and is followed by the bump of full dip and the bump of backcheck engaging tail. An extra bump during escapement blurs the player’s perception of that note’s articulation.
The third possibility has the two escapements trip simultaneously. Players like the clarity of this combined event, particularly if it feels consistent with neighboring notes. Speed of execution provides some wiggle room in crafting “simultaneous double escapement”. If one escapement segues immediately into the other, it feels like one event and if the jack is first to trip, a smoother combined bump will occur. So, the trick is to have the rep lever still supporting some knuckle weight and friction as the jack begins to let off but then immediately escape as if continuing the first escapement. The traditional method of slow letoff into drop misses these subtleties because it’s regulating to a secondary (and artificial) symptom rather than to the escapements themselves.
Nate Mills, RPT of the Augusta (GA) Music Box, does an excellent class on simultaneous double escapement called "You Don't Know Jack", featured recently in a live online event broadcast by the Charlotte NC PTG Chapter in memory of Jeffrey Owens, RPT. (Click here to see the YouTube video of it.)
Nate demonstrated how these escapements can be observed from behind the action (out of the piano) with hammers up by lifting the back of each key from rest through full stroke. Jack and rep lever rise together on their whippen and change direction from the rest of the whippen when tripped by letoff button and dropscrew respectively. Regulate the drop screw until jack and rep lever change direction simultaneously.
Hammer weight flexes the rep lever down slightly as it sits on the jack, allowing the repetition spring to slightly share the load. Because the double escapement timing was set to be simultaneous with no load, the loaded rep lever will arrive at the drop screw slightly later, creating the Escapement #1-into-Escapement #2 segue that feels like one bump.
Segued double escapement will improve playability in a grand action, well-regulated or not. But for accuracy and stability, it depends on the accuracy and stability of previous steps.
Next article, I will look at the steps that influence letoff, segue, and drop.