What Are the Red Stones in the Watch for?

Task and production of the bearing blocks for the movement.

Not only do they bring color and beauty to mechanical movements, but are also extremely useful: synthetic Ruby bearing stones play a prominent role in the foreground with bright red. For example, the Royal Oak Squelette Automatique from Audemars Piguet releases the view of the bearing stones in the clockwork from the back, as well as from the front side through the skeleton dial.

The natural enemy of any movement is the dust. This contains tiny, yet hard quartz particles that accumulate over time in the bearing. There they push themselves relentlessly into the material of the board and bridges, into the cones and shoots and let these parts wear out. The watchmakers of old times had to experience these disadvantages: the weak point of historical movements was the bearing, i.e. the hole in which the cone of a wheel shaft is guided. This hole was simply drilled into the work body. The friction resulting from the rotation of the cone caused the wear of the holes. That’s why we started to squeeze bearing bushes from other materials into the boards. This facilitated at least the subsequent renewal of the camp. However, the parts are still worn out very quickly.

Why were rubies chosen as material for the bearing bush?

Only the mathematician and astronomer Nicolas Fatio de Duillier (1664–1753), who was from Geneva, had the saving idea in London at the beginning of the 18th century: he stored the cones in a material that is harder than quartz. For this he chose the corundum, a mineral that is considered the second hardest gem after the diamond. The Corundum family includes sapphires and rubies, which are excellently suited as storage stones. Fatio de Duillier built 1704 the first watch whose balance was stored in Rubin. The procedure went to school: within a few years the rubies continued in the English watchmaking–initially as storage and cover stones for the balance wave, then also for the shafts of the wheel mill, until finally at 1720 the first, complete with ruby bearings Equipped watch was built. The use of Rubies has proved its worth: up to now, the bearings are used as drilled rubies, which, by their hardness, facilitate gliding and greatly reduce wear.

First, rubies of inferior qualities were processed into bearing stones. But then 1892 the French chemist Auguste Verneuil (1856–1913) succeeded in the artificial production of Rubin. He made Ruby Monocrystals grow, which are among the synthetic gems. These syntheses are not imitations, but minerals bred under artificial conditions. They do not only resemble the real gems externally, but also in the chemical composition, the crystal structure and the physical properties.

What are the advantages of synthetically produced storage stones?

Compared to natural Ruby, the synthesis has even more advantages when used as a bearing stone as well as for switching and raster elements in the movement: the crystal structure is completely homogeneous and the stone has no inclusions. These mono crystals are extremely abrasion resistant. There are now other methods for the production of synthetic gemstones. However, the crude for bearing stones is produced according to the method of Verneuil. Pulverized alumina is directed from above through a heat layer into a substance container. The powder melts, forms droplets and finally accumulates as a thin layer on a crystal germ at the bottom of the substance container. With five to ten millimeters per hour such a large, elongated body, pear or boule is growing. The addition of oxide – one to two percent – colours the corundum red. There is a great tension inside. Therefore, the melting bulb is separated or “relaxed” by heating before further processing of the length. During the subsequent slicing, the optical axis, the so-called C-axis, must be taken into account so that the optimum hardness is later achieved for the respective application purpose.

Today the bearing blocks are machine-made

Until the development of industrial production, the clock stones were made in painstaking, precise manual work. This required, among other things, pastes with powdered diamonds for grinding and polishing or diamond for rough machining. In a lathe, outside diameters were determined in several steps and the bore was made. The rough preliminary work followed the multiple, fine postprocessing.

Up to 45 minutes, an experienced craftsman needed to complete a single clock piece. Even before 1940, the industrial production of the Rubin Lochsteine began in large quantities, which shortened this production time by many different machines and cheapened: Bearing stones are bought by watch manufacturers today for cents following Localtimezone.org. Even in industrial production, 30 to 40 work steps and controls are necessary, depending on whether it is a simple cylindrical capstone without drilling, a bearing stone with bore and oil cut, in which a tiny droplet A straight or olive-shaped hole or a curved or straight stone. In addition, synthetic Ruby can also prismatic, pointed lifting stones for the armature as well as the most prismatic anchor stone of the balance, the so-called lever pin, which engages in the fork of the armature.

How is it possible to drill a hole in the hard synthetic ruby?

The production of a clock stone usually starts with the fact that the blanks are placed on the correct outer diameter. However, the manufacturers of the Watch stones usually do not take a further and important step in themselves: for the complicated task, the loch Pre, there are specialised companies which have the latest laser technology. After their work, the burnt edges of the borehole must be removed and the drilled holes placed on the exact correct dimensions. This is done, for example, by pulling the discs onto a steel wire and moving them back and forth mechanically. The process is repeated several times to precisely center the hole and to bring it to the exact measurement.

Now follows the grinding or Creusieren of the lowering of the sink, i.e. the recess on the side facing away from the cone. This spherical recess around the hole is installed in an automatic machine. The two sides of the stone are then sanded and polished, the outer and inner edges are rounded. The precise Polish has not only aesthetic reasons: the smoother the clock stone, the lower the friction – which prevents wear and has a positive effect on the gear reserve. Low tolerances apply: In the case of a clock stone with a diameter of one to two millimeters, with holes from 0.2 to 0.5 millimeters, accuracy is asked for thousandths of a millimeter.

The finished bearing blocks can be pressed directly into the PCB or found in high-quality plants in a ring of gold, the so-called Chaton, their place. The Chatons are often fastened with small screw and would offer the possibility to center it in a not exactly matching bearing stone. The high precision in manufacturing makes this function superfluous today: Today, Chatons are mere ornaments and surround the glowing red of the watch stones with a fine golden frame.

Tags: Audemars Piguet, automatic watches, clock hand lift