The balance wheel pivots are the thinnest in the watch, as they are the lowest torque. However they also carry what is often the heaviest wheel and so therefore are very vulnerable to break if the watch receives a shock. For pocket watches and clocks this was not a huge problem as they were generally kept safe, but a watch worn on the wrist spends most of its day on the move.
In 1790 Abraham-Louis Breguet invented the Para-chute device which was a spring which helped to absorb any shock to the balance pivots and keep it from breaking.
The modern day shock spring is based on the same principle; however it was not until the 1950s that the anti-shock system became widespread. Before this a broken balance staff was one of the most common fatal problems a watch would face.
Nowadays the shock system is so successful that a balance staff is rarely broken, and most damage can be traced to direct interference from someone who has opened the watch. This has led to current balance staffs actually being of a lower quality than those made 30+ years ago, with even the top tier watch houses choosing to chemically burnish the pivots with acid to save costs rather than burnishing them by hand as in years gone by.
Burnishing is where you rub a surface of metal smooth, compacting and hardening it in the process. All pivots are burnished to reduce wear, and as a result do not bend out of shape but shatter when force is applied
Modern day shock systems also help reduce the friction on the pivots, reduce contamination and oxidisation of the oil and ensure that the pivots are always centred.
The oil sink with a shock setting is usually reserved for the balance wheel pivots; both top and bottom, although on some higher end watches it is used elsewhere, specifically on the escape wheel.
As with most things in horology, everything has many names:
- The Setting can be called the Anti-shock Setting or just the Block
- The Chaton is sometimes known as the Free Setting
- The Balance Staff Jewel can be the Pivot Jewel
- The Cap Stone is often referred to as the Cap Jewel or End Stone
- And the Anti-Shock Spring could be the Shock Spring, or referred to by its brand name such as Incabloc
Function of the Parts
The spring is usually made out of brass, or a similar metal with elastic properties. It needs to be strong enough to absorb any shock and then return the Cap Stone and Chaton back into place
The Cap Stone is made out of synthetic ruby (aluminium oxide). It is curved at the top and flat on the bottom with a highly polished surface. It is immediately recognisable as it does not have a pivot hole in it. This holds the oil in place and in most modern watches is coated in a material (usually Fixadrop/Epilame) to prevent the oil spreading. It sits on top of the Chaton and is held in place by the Anti-Shock Spring and also to the Balance Staff Jewel through the capillary action of the oil
Balance Staff Jewel and Chaton
In almost all cases the pivot jewel will be friction fitted into the Chaton. Together they sit loose in the Setting, and are held down by the Anti-Shock Spring
The Setting is fixed to either the mainplate of the watch or the balance cock depending on whether it is the top or bottom Setting. It has the lock system that the Anti-Shock Spring uses to hold itself in place. It is shaped so that the Chaton will want to return to the centre when pushed down by the spring in normal conditions after a shock.
Types of Anti-Shock Spring
There are currently two main companies that make shock settings; Incabloc and Kif. Of these the most common setting in use is the Incabloc, mainly due to its use in ETA movements.
The shock systems can be split into two main groups, those that are fixed in place and hinge upwards, and those that are removable.
- Novodiac (made by Incabloc)
- Paraflex (made by Rolex)
- Etachoc (made by ETA)
- Duofix (made by Rolex)
Incabloc is owned by the Swatch Group (who also own ETA), whereas Kif is through a complex system part of Rolex. There is a story that Kif was formed due to an argument Rolex had with Incabloc many years ago, and so they decided to make their own “superior” shock system as a result.
To understand the need for the shock setting let’s take a look at how it evolved, and then we’ll take a look at how they work.
How an Anti-Shock System Works
The Chaton sits loose in the Setting, with the Balance Staff Jewel friction fitted into the Chaton and the Cap Stone sitting on top of the Chaton. The Anti-Shock Spring applies a downwards force on the Chaton and Cap Stone, holding it in place.
If a shock is received then the balance staff will push its shoulder against the Chaton and it will move both the Chaton and Cap Jewel with the Anti-Shock Spring flexing to allow this limited movement. This small movement absorbs the force of the impact in a safe way, thereby protecting the vulnerable balance staff pivot.
Once the shock has been absorbed, the spring’s elastic properties will mean it will want to return to its original shape and by doing so will push the Chaton and Cap Stone back downwards. The Chaton and Setting are shaped so that this downwards movement will guide the Chaton back towards its natural central position.
The educational website clockwatch.de has a wonderful Flash animation where you can apply a shock and watch how the Anti-Shock System works. You can follow this link: http://www.clockwatch.de/index.html?html/tec/sto/inc.htm
Examples of Anti-Shock Systems and How to Remove them