The Antikythera Mechanism Episode 6 - Making The Metonic Calendar Train

The Antikythera Mechanism Episode 6 - Making The Metonic Calendar Train, by Clickspring

In this video I make the gearing that drives the Metonic, Callippic and Olympiad pointers. If you're interested in a bit more detail on the ancient Greek approach to calendars, then I recommend this excellent article on the Athenian calendars - https://www.ancient.eu/article/833/the-athenian-calendar/

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Abbreviated Transcript:

01:16 So ignoring sign convention for the moment, and viewed from the perspective of the pointers, the gearing ensures that a full turn of th Metonic pointer occurs once every 3.8 years. And you might notice that two of the gears cancel out in the train calculation, so they appears to be redundant. But as it happens a 53 tooth gear turns out to be essential for another part of the mechanism thats driven by the first section of this train, and I'll cover that in detail in a later video Now there's a small error in the Metonic cycle thats corrected in the Callipic cycle, by essentially multiplying the entire Metonic cycle by 4 to give a more accurate 76 year relationship. And finally the Olympiad pointer indicates the passage of the 4 year Games cycle. So there are 6 wheel assemblies to be made to complete this part of the mechanism, as well as a number of supporting components.
02:54 Some were evolutionary dead ends, and simply didn't make it. Some, like the single pivot idea were the origins of an idea that continued to evolve. And others were evolutionary winners from the very beginning. Travelling through time essentially unchanged, right up to the modern era. Now one idea that of course definitely evolved is the tooth profile. But that's not to say it wasn't largely effective as it was. Because despite its mechanical inefficiency, a triangular tooth profile brings a tremendous advantage when it comes to certain aspects of the build. Like for example, depthing.
04:39 In that instance the entire outside profile of one or even both of the wheels can be very slightly filed back, much like when the teeth were originally formed. So that the final stage of depthing essentially becomes an extension of the tooth forming process.
12:42 so next I moved on to the pointer components, starting with the support frame for the metonic pointer. And since I'll soon need a second one of these for the Saros pointer, I figured I'd better make both of them at the same time.

References:

Gears From The Greeks - Derek de Solla Price: http://amzn.to/2pii4ZD

The CT and PTM data that the AMRP have made publicly available can be found here: http://www.antikythera-mechanism.gr/data

Gear schematic can be found in Tony Freeth's 2012 research paper:
http://dlib.nyu.edu/awdl/isaw/isaw-papers/4/

The Athenian Calendar - https://www.ancient.eu/article/833/the-athenian-calendar/

The Callippic Cycle: https://en.wikipedia.org/wiki/Callippic_cycle

Meton Of Athens/Metonic Cycle: https://en.wikipedia.org/wiki/Meton_of_Athens

MT Wright (2005) Counting Months and years: The Upper Back Dial of The Antikythera Mechanism

Credits:

Clips from "The 2000 Year Old Computer" courtesy Images First Ltd.

Digital image of the Back Dial of The Antikythera mechanism courtesy Tony Freeth, Images First Ltd

The Antikythera Mechanism Episode 6 - Making The Metonic Calendar Train, by Clickspring

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