Grand Seiko has released its first mechanical complication watch, the Kodo Constant-force Tourbillon, which is the first timepiece to combine a tourbillon and a constant-force mechanism into a single axis for greater stability and accuracy.

A constant-force mechanism is an important part of a mechanical watch movement that smooths out how it works and keeps it on time. Anyone who has played with a wind-up toy has seen how it starts moving quickly and slows down as the spring unwinds. The same is true in a watch. If the mainspring was connected directly to the gears, the hands would initially spin around like mad, then stop after a few minutes.

To keep this from happening, movements have escapements, which oscillate and stop the movement for an instant one or more times per second. Theoretically, this should make the watch keep time but in practice, things are very different. When the spring is wound, it exerts a lot of force, but as it unwinds, the pull becomes progressively weaker.

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This sets up forces that throw the escapement off and the timepiece becomes less accurate. To prevent this, a constant-force mechanism is introduced that sits between the mainspring and the escapement, evening out the energy of the spring so it’s released at a constant rate on a constant level.

Until now, if a watch had a tourbillon and a constant-force mechanism, they are in different parts of the movement and only interact through the gearing. In the Kodo, these are, for the first time, joined together on the same axis. It’s a design that Grand Seiko introduced in 2020 with the T0 Constant-force Tourbillon concept, but has now been incorporated into a finished watch in the form of a movement that is smaller than the concept prototype.

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According to Grand Seiko, this new arrangement simplifies the movement. Since there aren’t any gears between the tourbillon, which vibrates at eight beats per second, and the constant-force mechanism, which rotates at precise one-second intervals, there is no loss or change in torque, allowing for greater endurance and a stable amplitude of the balance.

It also allows the constant-force carriage to act as a small seconds hand as it turns.

The Grand Seiko Kodo Constant-force Tourbillon SLGT003 is powered by the 340-component, 44-jewel, manual Caliber 9ST, running at 28,800 vibrations per hour (eight beats per second) and is accurate to +5 to -3 seconds per day. The mainspring has a power reserve of 72 hours.

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This movement is set in a case made of Platinum 950 and Brilliant Hard Titanium with a box-shaped sapphire crystal with anti-reflective coating and a sapphire case back, giving it a water resistance to 330 ft (100 m, 10 bar). This is held on by a calf-leather strap with a Platinum 950 three-fold clasp with push-button release. If you don’t like that, a double-sided crocodile strap is also included.

The Grand Seiko Kodo Constant-force Tourbillon will be available in a limited edition of 20 units starting in October 2022 and one will set you back US$350,000.

The video below introduces the Grand Seiko Kodo Constant-force Tourbillon.

Source: Grand Seiko