A rotor, also known as an oscillating weight or mass, is a key component of all automatic watch movements. The rotor dates back to 1777 when Swiss horologist Abraham-Louis Perrelet created a self-winding mechanism equipped with a rotor that winds the spring accurately in both directions; this became known as a perpetual watch or perpétuelle, due to its eternal motion. Perrelet’s invention didn’t really take off at the time, as it was built for pocket watches, which remain fairly stationary in the pocket most of the time, meaning the movement did not get enough energy to keep it running. That and the fact that it was comparatively expensive to make.
Related: Mechanical vs Quartz; A Guide To The Different Types Of Watch Movements
With the advent of wristwatches, the rotor serves an indispensable function in any automotive movement. As you move, the rotor, or oscillating weight, swings in a circle which works to wind the watch. The rotor can typically be found on the back of the watch movement, with the three main types being traditional central rotors, micro-rotors, and peripheral rotors.
The main types of rotors in automatic watch movements
Central rotor
The most common type of watch rotor is a centrally mounted semicircular weight that is crafted from stainless steel or precious metals like gold or platinum. A central rotor is positioned on top of the movement and conceals around half of the back of the movement when at rest; as you move throughout the day, the rotor winds you watch by swinging in one or both directions. Many luxury manufactures use the rotor as a canvas to showcase their métiers d’art, decorating it with guilloché, Côtes de Genève stripes, or engravings.
Micro-rotor
As the name suggests, a micro-rotor is a smaller version of a traditional rotor. While standard centrally mounted rotors rest atop the movement, micro-rotors are recessed into the movement, allowing for a more streamlined movement (and as a result, a thinner case). Piaget, the master of ultra-thin watches, was a pioneer of the micro-rotor, with the component appearing in its seminal 1200P and 1208P movements. Micro-rotors are also utilised by watch brands like Patek Philippe, Chopard, Laurent Ferrier, Bulgari, and Parmigiani Fleurier. On the more affordable side of the spectrum, the Baltic MR01 uses a Hangzhou-sourced automatic movement with a micro-rotor.
Peripheral rotor
A less common type of rotor, the peripheral rotor deviates from the visual language of the standard rotor and micro-rotor. A peripheral rotor is designed to swing around the edge (i.e. the periphery) of the movement. This allows watchmakers and manufactures to produce an ultra-thin movement without the aid of a micro-rotor; the advantage of the peripheral rotor being that it showcases more of the movement. Currently, Carl F. Bucherer is the leader in peripheral rotor technology and was the first brand to introduce a peripherally wound automatic movement into its core lineup, in the form of the Manero Peripheral range. In a display of ultra-thin watchmaking virtuoso, Bulgari used a peripheral rotor in the Octo Finissimo Tourbillon Chronograph, which (at the time of writing) is the thinnest tourbillon chronograph watch in the world.
Skeletonised rotors
While technically a standard rotor, the skeletonised rotor deserves a special mention. Manufactures like Cartier and Parmigiani Fleurier have employed skeletonised rotors in their timepieces; the former’s Masse Mystérieuse watch sees the entire automatic movement actually contained within the skeletonised rotor, while the latter features a more traditional take in its Tonda PF Skeleton watch.
Avant-garde rotors
Some manufactures eschew convention altogether, not simply decorating the rotor but transforming it into a veritable work of art in its own right. Released in 2011 to celebrate its patronage of the Russian Bolshoi Theatre, the Audemars Piguet Jules Audemars Extra-Thin Bolshoi has an exhibition caseback that reveals the Bolshoi Theatre engraved into the centrally mounted movement.
Speake-Marin has its own take on the centrally mounted rotor, forging the traditional semicircle shape for an openworked style that takes up the whole movement. The Omega Aqua Terra James Bond has styled its centrally mounted rotor after the barrel of a gun, while the MB&F Legacy Machine FlyingT series swaps the semicircle for a sun-shaped rotor.
Enjoyed this article? Check out our Ultimate Guide To Watches here; covering everything from the types of watch movements to watch styles and complications.
Words by AR Staff
