The complete picture of the Moritz Grossmann movement, inheriting the pure German tradition ❹

Moritz Grossmann's new bass movement
Cal. 102.0, released in 2015.
While the company has always placed the highest priority on robustness, this time it has also paid close attention to expandability and aesthetics.
This was made possible by an offset drive train.
How did the design team manage to fit this difficult-to-handle "modern gear train" into the watch?

MuMoritz Grossmann has always placed a high priority on robustness when designing its movements. Their philosophy of making movements as large and thick as possible without considering expandability has given their movements the robustness of classic pocket watches. However, the company appears not to have been indifferent to the trend toward thinner and more compact movements. The Tefnut, released in 2015, is equipped with the new Caliber 102.0 movement, which combines robustness and thinness. Generally, the thinner and smaller a movement, the worse its durability and accuracy become. The history of modern wristwatch movements has been about how to improve these characteristics, rather than letting them worsen. Jens Schneider and Norwiet Windecker, who were responsible for the designs, explain the design elements of the 102 series as follows:

"There were two aims: to create a base on which to mount additional functions, and to more clearly show the movement's design." The reason "toughness" was not listed as a condition is because it goes without saying for the company. 　To incorporate additional functions, the movement needs to be made thinner. For this reason, Windecker adopted an offset gear train for the 2 series. An offset gear train, which does not place the second wheel at the center, is prone to hands jumping when setting the time, but because the second wheel, barrel, and balance do not overlap, the movement can be designed to be thinner. 　Most automatic movements since the 1980s use this type of gear train, but it is almost nonexistent in hand-wound movements, with the exception of thin movements from brands like Piaget. This is because it requires unique know-how. Fortunately, however, Grossmann had a solution: a leaf spring attached to the hour wheel to prevent the hands from skipping. Furthermore, if you look at the gear train of the 102 series, the hour and minute hands are driven not by an offset "second wheel" but by a thick "second pinion" located in the center of the movement. In other words, while it looks like a typical offset gear train, it is actually a modified version of a standard gear train with the second wheel located in the center. Combined with the leaf spring, the hands almost never skip when setting the time. However, the aim of adopting this modified gear train goes beyond thinness. "By offsetting the gear train, the independent balance is emphasized. It is well known in horology that space efficiency is improved when the balance and barrel are roughly the same diameter," said Windecker. In addition, the diameters of the fourth wheel (sixth wheel in the 102 series) and the crown wheel are also roughly the same, and the barrel and gear train bridges are purposely cut in straight lines. It may be difficult to see in the classic finish, but the offset gear train and the size and shape of the parts show that the design of the 102 series is extremely modern.

Cal. 102.0 This manual-winding movement features a structure that emphasizes the balance wheel. The second wheel is off-center and the baseplate is flat, resulting in a clean design. While its 26.0 mm diameter and 3.45 mm thickness are by no means thin, they are nothing short of impressive when you consider the dimensions, which were chosen with robustness in mind.

Cal. 102.0 seen from the back. Windecker's intention of "creating a simple and beautiful movement" is clear. What can be seen in the center is not the "second wheel" but the "second pinion." The barrel can be seen slightly from the 3/5 plate, as "the barrel is the most beautiful part, so I wanted to give it a glimpse."

Windecker added a few more aesthetic considerations. The ARCAP gears used from the Benu Tourbillon onwards were intended to unify the movement's colour to silver. Furthermore, the fine regulator mechanism that was previously mounted on the balance cock has had its adjustment range narrowed and is now housed within the balance cock. Windecker is even more of a "principler" than Schneider when it comes to the position of the regulator. He has a history of teaching at A. Lange & Söhne's watchmaking school. "In a well-adjusted movement, the regulator should naturally be located in the centre of the balance cock." 　Schneider adds, "Even when drilling a hole in the balance wheel to remove one-sided weight, if you drill too much it will look ugly. I don't like to drill too much, and I design the movement from the ground up to prevent this from happening." 　The baseplate, which has been shaped as flat as possible, is also the result of aesthetic considerations. Advances in machine tools have made it possible for modern movements to have complex shapes on the baseplate. This has increased productivity, but it cannot be said to be aesthetically pleasing. In contrast, Windecker has given this "modern hand-wound" a baseplate with no bumps, just like the pocket watch movements of yesteryear. In the past, the poor quality of machine tools meant that the baseplate had to be flat. However, in the 102 series, this was deliberately reproduced for aesthetic reasons. This is likely one of the reasons why the design of the 102 series is reminiscent of pocket watch movements from the 18th and 19th centuries.

　Even with aesthetics in mind, Moritz Grossmann never neglects the watch's functionality as a watch. The opening on the back of the main plate has been made extremely small, and unnecessary holes have been removed. This is to ensure the rigidity of the thin main plate. Perhaps because they didn't want to cut down the main plate, the stop-seconds mechanism is thinner and simpler than the Benu. However, considering the relatively smaller moment of inertia of the balance wheel, this is sufficient. The winding mechanism has also been made smaller, but to increase durability, it has been further unitized and some parts have been reinforced. Incidentally, I don't like putting a small-diameter movement in a large case. Not only does it detract from the aesthetics, but it also places greater strain on the movement. However, Grossmann has responded by strengthening the winding mechanism. The scalability of the watch as a "general-purpose watch" is also reflected in the winding mechanism.
　The consideration for durability is also evident in the relationship between the barrel and balance. The mainspring torque is 700g-mm. It's weaker than the ETA2892-A2, but slightly stronger than the Pezeau 7001. However, the balance wheel's moment of inertia is 13g-cm2, nearly three times that of the Pezeau. The reason a weak mainspring can rotate a large balance wheel and still extend the power reserve is due to what Windecker calls a "weak balance spring." Incidentally, I'm not a fan of the modern design concept of weakening the balance spring's elasticity to increase the balance wheel's inertia or extend the power reserve. However, increasing the frequency from 18,000 vph to 21,600 vph would be perfectly acceptable. Grossmann incorporates modern design concepts without going overboard.

Upper left: A modified offset gear train that does not place the second wheel in the center. To give the watch a unified appearance, all the gears are made of silver ARCAP. A smooth baseplate is also used for the same reason.
Upper right: The torque of the mainspring of Cal.102.0 is standard at 700g-mm. However, it uses the same jewel-bridge barrel as the Benu Tourbillon, and is compatible with eccentricity countermeasures and accelerometer adjustment.
Bottom left: The beryllium copper balance wheel has a relatively large moment of inertia of 13g·cm2. The swing angle at time T0 is approximately 300 degrees, and remains at approximately 270 degrees at time T24. The horizontal and vertical deviation is also excellent, remaining within 20 to 30 degrees.

　The Caliber 102 series was originally designed as a two-hand movement. However, the Japan-limited model released in 2016 features a second hand at the 7 o'clock position. As the photo shows, even with the addition of a second hand, which was not intended at the time of design, the dial layout remains natural. While the insight of the Japanese subsidiary that planned it is certainly admirable, the skill of the design team, who designed it so that it would not look out of place even with the addition of a second hand, is what should be praised. The new Caliber 102 series places emphasis on scalability. The design is, as expected, full of the originality and careful consideration that is characteristic of Moritz Grossmann.