The Antikythera Mechanism Episode 5 - The Input Crown Wheel Assembly

• Report rights infringement
• published: 24 Sep 2017
• views: 222929

The Antikythera Mechanism Episode 5 - The Input Crown Wheel Assembly In this video I make the small assembly that enables the user to drive the mechanism. If you would like to help support the creation of these videos, then head on over to the Clickspring Patreon page: https://www.patreon.com/clickspring ________________________________________________________ A very special thank you to Patrons: Sinking Valley Woodworks (http://www.sinkingvalleywoodworks.com) Glenn Trewitt Christopher Warnock Mike Manfrin Andrew Smith Bernd Fischer Rudolph Bescherer Jr Sam Towne Adam Slagle Jack Cause Jeremiah G. Mort Dave Seff Matteo Neville Olof Haggren Stassinopoulos Thomas Florian Ragwitz Larry Pardi Samuel Irons Tim Bray Andre van Soest Pete Askew Norman Lemke ________________________________________________________ Abbreviated Transcript: 0:00:56 Now much like the main solar drive wheel, from our modern perspective, this is clearly not the easiest way to construct the part. So again the question naturally arises, why did The Maker choose this more difficult method? Its possible that it was due to the turning limitations of the period. And certainly its easy to imagine that forming a small recess like this might not have been entirely straightforward. 03:08 Taking care to reheat the work as soon as it started to cool down, and also being careful to not to overheat it. It doesn't take much to melt a small piece of brass like this. A light skim cut on the lathe created a uniform surface, and widened the inside diameter to be a close fit with the central cylinder formed earlier. A touch of soft solder bonds the two parts together, and fills the join in the perimeter of the band. I'll be sure to position that join to coincide with the root of a tooth when I form the teeth later. 06:57 Gradual increases in the depth of cut on either side of a single tooth, eventually leave a small triangular land at the tooth apex. At which point the carriage can be locked, and all of the teeth cut at the same setting. I took a light skim cut of the perimeter to remove the small exit burr left by the fly cutter, and then marked out the rectangular hole that will receive the driving arbor. 08:25 Now you'll recall from a previous episode, that I'd like to keep the whole structure open throughout the build to give you a good clear view of what's goin on. So for at least the duration of the build, support for the input arbor will be provided by this bracket, pinned to the main plate. A key feature of the bracket is that crisp 90 degree bend, which I formed by milling out a V groove in the raw stock. 09:49 I've found that around 0.4 of a millimeter gives a good tight radius to the bend, and allows the metal to bend easily without cracking. The inside corner on the indexing arm, that I made in a previous video, serves as a convenient square reference. And I'm being very careful here not to bend back and forth too much, to avoid work hardening the join which would increase the risk of cracking the thin metal. 12:27 The wheel assembly could be held up to B1 with a toolmakers clamp, depthed, marked and then permanently fixed in place. But I'd also like to have the back surface of the bracket flush with the side of the main plate, without having to trim that plate after the fact. So that meant making my best guess at the correct depthing at the planning stage, and essentially locking it in at the start of the project. 13:18 With the input assembly position located, the bracket and underlying main plate were drilled out to accept a pair of steady pins. The steady pins now ensure the the accuracy and repeatability of the bracket position. And once clamped firmly, I drilled out the hole for the bracket retaining pin. A quick tidy up of the holes, and that's the bracket complete for now. 16:44 I opened up the matching rectangle marked out in the center of the crown wheel, taking care to ensure a close fit. With the crown wheel assembled on its driving arbor, I marked the retaining pin position, which will ensure a small clamping force from the taper pin once its inserted. 19:05 The friction is quite low, with both wheels showing free and smooth movement. And the gear interaction feels good too, much better than I expected from a triangular tooth form. In fact based on the feel alone, there's not much to give away the fact that its not a modern tooth profile. In the next video, the mechanism will continue to take shape, as I make a start on the calendar and eclipse gearing. References: Gears From The Greeks - Derek de Solla Price https://www.amazon.com/Gears-Greeks-Antikythera-Transactions-Philosophical/dp/0871696479 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 Antikythera Mechanism Episode 5 - The Input Crown Wheel Assembly