What is a rack-strike mechanism?

Rack Strike Movement

The advantage of having a rack-strike mechanism is that the hands and striking mechanism stay synchronized. If you have ever owned a "thirty-hour" clock, you will appreciate the advantages of this mechanism.

Please refer to the diagram detailing the different parts and showing the mechanism. The following will detail how a rack-strike mechanism works.

Power from the time train is transferred from the minute arbor (N) to the hour wheel (A), then subsequently transferring power to the minute wheel (B). The minute wheel rotates, once per hour, and has a pin (D) that as it approaches the top of the hour lifts the lifting arm (E) which raises the rack hook (F). After the rack hook is raised the rack is released (J) which drops to the left with the aid of the spring (L). This process is known as the "warning".

The amount the rack falls back is determined by the rack pin (M) which is attached to the rack tail (K). The rack pin falls to the snail gear (C) which is fixed to the hour wheel (A) and rotates once every twelve hours. As you can see, the snail has twelve steps. The deeper the steps are cut, the more towards the center the rack tail will drop allowing the rack to drop more to the left. This process generates the one-to-twelve-count.

At the hour the lifting arm (E) drops off the pin (D) and the clock striking mechanism is released and allowed to strike. The striking is achieved by the gathering pallet (G) rotating thus moving the rack (J) one tooth, at a time, back to the reset position. Each rotation of the gathering pallet corresponds to an hour strike. On the last tooth the striking is halted by the gathering pallet being stopped by the rack pin (H).