How the winding gears work

[KBH 7]

AUTOMATIC WINDING

The ETA Caliber 2842-2824-2836, etc.

 

The automatic winding watch converts motion of the wearer's wrist into power that winds the mainspring of the watch. As show left (in an inverted position), most such watches use a central rotor with a gear (yellow arrow). As the rotor moves around its central pivot, the gear winds the watch.

 

 

 

In the second photograph, a typical contemporary automatic winding system is shown with the central rotor removed. This is a ETA caliaber 2842. Identified parts include (1) the opening for the winding stem. (2) The crown wheel (which transfers power from the winding stem to the ratchet wheel, arbor, and mainspring during hand winding). (3) The ratchet wheel (on top of the barrel and attached to the arbor and mainspring at the center of the barrel). (4) The mainspring barrel itself. (5) The twin click-wheels that receive power from the wheel on the central rotor (above). (6) and (7) the reduction and transfer wheels that transmit power from the twin click-wheels to the ratchet wheel.

 

Because the ratchet wheel must always wind the mainspring in one direction (counterclockwise in the view at left), the twin click-wheels convert rotation of the central rotor in either direction into power that will wind the mainspring.

 

Bi-Directional Winding

 

 

 

The twin click-wheels are each constructed of two parts, an upper and lower section (as shown in the diagram, left).

 

These upper and lower halves are locked or unlocked (with one-way ratchets), depending on the direction of rotation of the upper section. While both upper sections always rotate, the lower section rotates only on the locked wheel. With the central rotor moving clockwise, only the right click-wheel is locked. With the central rotor moving counterclockwise, only the left click-wheel is locked. This is the difference that allows the mechanism to utilize rotor rotation in both directions.

 

The upper illustration shows power flow (yellow arrows) with clockwise rotor rotation, the lower with counterclockwise rotation.

 

 

 

Note: When one of the bi-directional gears fails, this is the main cause of low power reserve. This allows the rotor to spin freely and release the spring tension.