Mainspring - How they work

The mainspring is wound by turning the arbor, but drives the watch movement by the barrel; this arrangement allows the spring to continue powering the watch while it is being wound. Winding the watch turns the arbor, which tightens the mainspring, wrapping it closer around the arbor. The arbor has a ratchet attached to it, with a click to prevent the spring from turning the arbor backward and unwinding. After winding, the arbor is stationary and the pull of the mainspring turns the barrel, which has a ring of gear teeth around it. This meshes with one of the clocks gears, usually the center wheel pinion and drives the wheel train. The barrel usually rotates once every 8 hours, so the common 40-hour spring requires 5 turns to unwind completely.

Mainspring - Fusee

The fusee was a much longer-lasting innovation. This was a cone-shaped pulley that was turned by a chain wrapped around the mainspring barrel. Its curving shape continuously changed the mechanical advantage of the linkage to even out the force of the mainspring as it ran down. Fusees became the standard method of getting constant torque from a mainspring. They were used in most spring-driven clocks and watches from their first appearance until the 19th century when the going barrel took over, and in marine chronometers until the 1970s.

Mainspring - Stackfreed

The stackfreed was an eccentric cam mounted on the mainspring arbor, with a spring-loaded roller that pressed against it. The cam had a 'snail' shape so that early in the running period when the mainspring was pushing strongly, the stackfreed would provide a strong opposing force, while later in the running period as the force of the spring decreased, the opposing force of cam would also decrease. The stackfreed added a lot of friction and probably reduced a clock's running time substantially; it was only used in some German timepieces and was abandoned after about a century.

Mainspring - Stopwork

Another early device which helped even out the spring's force was stopwork or winding stops, which prevented the mainspring from being wound up all the way, and prevented it from unwinding all the way. The idea was to use only the central part of the spring's 'torque curve', where its force was more constant. The most common form was the Geneva stop or 'Maltese cross'. Stopwork isn't needed in modern watches.

Peter Henlein - Mainspring

The mainspring which made portable clocks possible, often attributed to him, actually appeared in the early 15th century, almost a century before his work. Although he did not invent the mainspring, the production of his portable watches was made possible primarily by a previously unseen scale of miniaturization of the torsion pendulum and coil spring mechanism, placed in a technical unit by Peter Henlein, a technological innovation and novelty of the time, operating in all positions; which makes him to the inventor of the watch.

Mainspring - Self-winding watches and 'unbreakable' mainsprings

Self-winding or automatic watches, introduced widely in the 1950s, use the natural motions of the wrist to keep the mainspring wound. A semicircular weight, pivoted at the center of the watch, rotates with each wrist motion. A winder mechanism uses rotations in both directions to wind the mainspring.

Mainspring - The myth of 'overwinding'

One cause of “overwinding” is dirt. Watch movements require regular cleaning and lubrication, and the normal result of neglecting to get a watch cleaned is a watch stopped at full wind. As the watch movement collects dirt and the oil dries up, friction increases, so that the mainspring doesn't have the force to turn the watch at the end of its normal running period, and it stops prematurely. If the owner continues to wind and use the watch without servicing, eventually the friction force reaches the 'flat' part of the torque curve, and quickly a point is reached where the mainspring doesn't have the force to run the watch even at full wind, so the watch stops with the mainspring fully wound. The watch needs service, but the problem is caused by a dirty movement or other defect, not "overwinding".

Mainspring - Motor or safety barrel

In the motor barrel, the functions of the arbor and barrel were reversed from the going barrel. The mainspring was wound by the barrel, and turned the arbor to drive the wheel train. Thus if the mainspring broke, the destructive recoil of the barrel would be applied not to the wheel train but to the winding mechanism, which was robust enough to take it.

Sarah Hayes (musician) - Mainspring

Hayes released her debut EP Mainspring in 2013.

Mainspring - Hazards

The mainspring contains a lot of energy. Clocks and watches have to be disassembled periodically for maintenance and repair, and if precautions are not taken the spring can release suddenly, causing serious injury. Mainsprings are 'let down' gently before servicing, by pulling the click back while holding the winding key, allowing the spring to slowly unwind. However, even in their 'let down' state, mainsprings contain dangerous residual tension. Watchmakers and clockmakers use a tool called a "mainspring winder" to safely install and remove them. Large mainsprings in clocks are immobilized by "mainspring clamps" before removal.

Mainspring - History

Mainsprings appeared in the first spring-powered clocks, in 15th-century Europe. It replaced the weight hanging from a cord wrapped around a pulley, which was the power source used in all previous mechanical clocks. Around 1400 coiled springs began to be used in locks, and many early clockmakers were also locksmiths. Springs were applied to clocks to make them smaller and more portable than previous weight-driven clocks, evolving into the first pocketwatches by 1600. Many sources erroneously credit the invention of the mainspring to the Nuremberg clockmaker Peter Henlein (also spelled Henle, or Hele) around 1511. However, many references in 15th-century sources to portable clocks 'without weights', and at least two surviving examples, show that spring-driven clocks existed by the early years of that century. The oldest surviving clock powered by a mainspring is the Burgunderuhr (Burgundy Clock), an ornate, gilt chamber clock, currently at the Germanisches Nationalmuseum in Nuremberg, whose iconography suggests that it was made around 1430 for Philip the Good, Duke of Burgundy.

Mainspring - The myth of 'overwinding'

Another common cause of “overwinding” is that if a watch is dropped then the balance staff can break and the watch can no longer run even when the mainspring is fully wound.

Mainspring - Self-winding watches and 'unbreakable' mainsprings

In automatic watches, motion of the wrist could continue winding the mainspring until it broke. This is prevented with a slipping clutch device. The outer end of the mainspring, instead of attaching to the barrel, is attached to a circular expansion spring called the bridle that presses against the inner wall of the barrel, which has serrations or notches to hold it. During normal winding the bridle holds by friction to the barrel, allowing the mainspring to wind. When the mainspring reaches its full tension, its pull is stronger than the bridle. Further rotation of the arbor causes the bridle to slip along the barrel, preventing further winding. In watch company terminology, this is often misleadingly referred to as an 'unbreakable mainspring'.

Mainspring - How they work

In the form used in modern watches, called the going barrel, the mainspring is coiled around an arbor and enclosed inside a cylindrical box called the barrel which is free to turn. The spring is attached to the arbor at its inner end, and to the barrel at its outer end. The attachments are small hooks or tabs, which the spring is hooked to by square holes in its ends, so it can be easily replaced.

Mainspring - How they work

The mainspring is coiled around an axle called the arbor, with the inner end hooked to it. In many clocks, the outer end is attached to a stationary post. The spring is wound up by turning the arbor, and after winding its force turns the arbor the other way to run the clock. The disadvantage of this open spring arrangement is that while the mainspring is being wound, its drive force is removed from the clock movement, so the clock may stop. This type is often used on alarm clocks, music boxes and kitchen timers where it doesn't matter if the mechanism stops while winding. The winding mechanism always has a ratchet attached, with a pawl (called by clockmakers the click) to prevent the spring from unwinding.

Mainspring - Going barrel

The modern going barrel, invented in 1760 by Jean-Antoine Lépine, produces a constant force by simply using a longer mainspring than needed, and coiling it under tension in the barrel. In operation, only a few turns of the spring at a time are used, with the remainder pressed against the outer wall of the barrel. Mathematically, the tension creates a 'flat' section in the spring's 'torque curve' (see graph) and only this flat section is used. In addition, the outer end of the spring is often given a 'reverse' curve, so it has an 'S' shape. This stores more tension in the spring's outer turns where it is available toward the end of the running period. The result is that the barrel provides approximately constant torque over the watch's designed running period; the torque doesn't decline until the mainspring has almost run down.

Mainspring - Remontoire

A fourth device used in a few precision timepieces was the remontoire. This was a small secondary spring or weight which powered the timepiece's escapement, and was itself rewound periodically by the mainspring. This isolated the timekeeping element from the varying mainspring force.

Mainspring - Motor or safety barrel

Around 1900, when broken watchsprings were more of a problem, some pocketwatches used a variation of the going barrel called the motor barrel or safety barrel. Mainsprings usually broke at their attachment to the arbor, where bending stresses are greatest. When the mainspring broke, the outer part recoiled and the momentum spun the barrel in the reverse direction. This applied great force to the delicate wheel train and escapement, often breaking pivots and jewels.

Mainspring (novel) - Plot summary

Mainspring is the story of a young clockmaker's apprentice, who is visited by the Archangel Gabriel. He is told that he must take the Key Perilous and rewind the mainspring of the Earth. It is running down, and disaster to the planet will ensue if it's not rewound. From innocence and ignorance to power and self-knowledge, the young man will make the long and perilous journey to the South Polar Axis, to fulfill the commandment of his God.

Mainspring gauge - References

* Watkins, Richard: Mainspring Gauges and the Dennison Combined Gauge, 2009.