The month lifting lever drives a ratchet that advances the month wheel. The month drum is driven off the date wheel shaft by a lifting cam that raises the month lifting lever. The 31-tooth date wheel is advanced by a ratchet pawl on the back side of the next lever in the lifting linkage in a similar manner to the day of week wheel, and the date wheel is arrested after advancing one day by the stopping lever coming from the right side of the mechanism. The date hand shaft has 31 teeth at the back of the mechanism – one for each date of the month, and at the front of the mechanism is the ratchet mechanism that prevents the date hand from moving backwards. The date hand is driven by the right lifting rod from the main lifting arm behind the time movement. The day wheel is driven by a ratchet mounted on the drum side of the lever connected to the main lifting arm. The rear pawl prevents the wheel from going forward other than when lifted by the mechanism, the front prevents the wheel from reversing. The two pawls at the top of the wheel lock the wheel into position so that it only advances one day at a time. The wheel takes two weeks to rotate fully. The wheel on the right side of the drum has 14 teeth, one for each day. The day of week drum is relatively simple. The right rod is connected to another rachet mechanism that drives the date of the month mechanism, which in turn drives the month drum. The left rod is connected to a ratchet mechanism that drives the day of the week drum. This lever raises two rods that drive the left and right sides of the calendar mechanism. This wheel drives a kidney-shaped cam that in turn raises the main lifting lever. The calendar mechanism is driven from the time train by a wheel that rotates once per day. After that, Seth Thomas migrated to using the Andrews mechanism which uses a snail-shaped cam. The Mix Brothers calendar movement was used on the early Office Calendars from 1863 to sometime in the 1870’s. ![]() ![]() Seth Thomas used 3rd party calendar mechanisms in many of their clocks the mechanism in my Office No 2 is the Mix Brothers variant which has a kidney-shaped cam driving the calendar mechanism. This clock goes one step further – it actually compensates for leap year. In short, this means the clock knows how many days each month has – February has 28, December has 31, etc. Time is displayed on the top 14″ dial, and the day of the week, date, and month are shown on the lower dial of the same size. They were made from about 1863 – 1890 and stand 44″ tall. 2 is a large weight driven double dial calendar clock.
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