The Antikythera Mechanism Episode 9 - Making The Epicyclic Pin and Slot Gearing

G'day chris here and welcome back to clickspring In this video I make the small gearing module that models the ancient Greek understanding of the variable motion of the moon In modern astronomical terms, there are two components to this variable motion There's the slight variation in speed as the moon follows what we now understand to be in elliptical orbit and then there's the slow procession of the axis of that orbit that slightly Extends the time it takes for the moon to come back to the same place within the orbit itself this is known as the anomalistic month and The motion is neatly captured within the gearing of this next part of the mechanism using two separate inputs The first input is the mean sidereal period of the moon and it drives a gear on the e assembly platform That is a small pin on its upper face The pin fits into a small slot on a gear located directly above it and the two rotate together Ordinarily this would serve no purpose But the gear with the pin turns on a slightly offset access to that of the gear with the slot So that as they turn together the slot gear is forced to travel at a variable speed I've added reference lines to show how the slot gear Oscillates between being slightly ahead and then slightly behind the driving gear as it goes through each revolution The slot gear travels fastest when the pin is closest to the axis of rotation and slowest when it's farthest away With the result being that the mean sidereal period now has a cyclical variation to it now at the same time the maker contrived a second input to drive the platform upon which these gears are mounted introducing a second component to the variable motion and You recall from previous videos that the 53 tooth gear cancelled out of each of the metonic and Sarah strained calculations that it remains in the calculation for this section of the train and in fact its purpose is now revealed to assist in Calculating the correct period for the precession of the lunar orbit By mounting the pin and slot gearing epicyclicly on this platform The two variable components of the lunar motion are now combined to model the anomalistic month And as if that wasn't impressive enough the output was then sent via coaxial shaft back through the input hub and Handed off to another shaft that drove the lunar phase assembly on the front face of the mechanism Prior to its discovery amid the antique ether wreckage the classical texts had already suggested that something along these lines existed in antiquity. For example the account from Cicero Someone could be argued that the physical evidence of mathematical gearing of some sort should have been expected from the period But there was nothing on the record to suggest that it would be anything like this such a sophisticated design modeling an astronomical concept that's hard enough to describe with words let alone gears and Executed with a technical confidence that can only come from long experience and a deep knowledge of the craft of constructing find mechanism Which naturally leads to the conclusion that it was the product of a well-established engineering tradition that was much broader and more capable than had been previously imagined and about which we presently know very little And that final fact means that it largely falls to the mechanism itself to tell the story to hint at the tools used and to guide the speculation about how such a machine might have been created more than two thousand years ago This small hub forms the basis of the component that I introduced at the end of the previous video the mean lunar sidereal input assembly And with the flats formed the holes in the wheels were formed to match The smaller one to be a permanent fit on the hub and the larger removable to permit disassembly from the e platform This small assembly rotates on the e Arbor which is the final output of the pin and slot module and at the same time It's the primary bearing surface for the e platform. So that puts the the Arbor at the center of quite a complex coaxial structure The various steps shoulders on the Arbor are also responsible for setting vertical clearances throughout this section of the train All of which makes it one of the most critical components of the machine This Arbor carries two wheels The larger one receives the output of the pin and slot mechanism and the smaller one hands off that rotation to the lunar phase shaft And here's a closer look at how this set of concentric assemblies comes together with the larger e platform components absent to make it easier to view It's a complex stack of step shoulders and bearing surfaces that all serve to keep the various wheels and assemblies not only aligned for meshing, but also appropriately separated from each other and so operating at minimum friction The pin and slot wheels interface directly with this stack of gears and of course need some specific mounting hardware to perform as intended starting with the eccentric pivot And with that pivot complete the various components that make up the pin and slot module were brought together to be hand fitted into position The pivot location on the e platform was determined by depthing the pinwheel with the lunar sidereal input wheel and Again much like the rest of the mechanism that depth thing can be determined using direct observation and a simple tool With the depthing of the wheels confirmed the pin and slot features were formed next The other key pieces of mounting hardware are the lugs and bridge strap that serve to restrain the pin and slot wheels in position The strap appears to have been bent to shape from a thin section of sheet metal So I've made a set of simple forming tools that I think could have plausibly been used to shape the part The retaining lugs were formed in the same way as those used to fasten the e platform together and the bridge strap was used to identify their position on the e platform After confirming the fit of the bridge strap the two retaining lugs and the eccentric pivot were permanently fastened into place The holes for the retaining pins in the e arbor were also formed, the top one being essential to retaining the entire assembly in place When the machine is inverted And with that the main components of this complex assembly are complete so here's how it all goes together This part of the machine is a little unusual in the sense that it can be considered a self-contained module So unlike most of the mechanism it's performance can be examined that assessed independently from the rest of the machine Much like a mechanical clock the main challenge at this point is to identify any localized binding of the components So it's easy to imagine testing like this being carried out on the original device Checking for freedom of movement and observing the pin and slider operation before it was finally installed within the mechanism And this brings us to a key moment of the reconstruction Because for the first time a significant portion of the device can be viewed and operated as a functioning mechanism As expected the friction has increased due to the nature of the gearing that's been added in this section But it remains at an acceptable level the input has a light feel and there's a comfortable free movement of the gearing and Although there's still a long way to go in this build, the full vision of the maker is now starting to emerge of a compact mechanical platform upon which then state-of-the-art astronomical concepts could be represented and combined into a single all-encompassing model of the cosmos Thanks for watching I'll see you later

Channel: Clickspring

Views: 540,210

Rating: 4.9753408 out of 5

Keywords: Antikythera, antikythera mechanism, hellenistic, greek, ancient greece, clockmaking, clickspring, bronze, brass, the antikythera mechanism, sidereal, sidereal month, pin and slot, pin and slot gearing, epicyclic, epicycle, epicyclic gearing, hipparchos

Id: v19cu2hj2Ms

Length: 17min 17sec (1037 seconds)

Published: Sat Oct 20 2018

Reddit Comments

[u/fenrisulfur]

Finally Chris shows that he is at least human, this is the first time I've seen a shitty tool on any of his videos.

Notice the shitty Chineseum needle nose pliers he uses to fish out the bracket from the coals.

[u/handpaw]

The eccentric gearing is so simple, yet, so complex and precise.

I was waiting for him to comment on how he arrived at the amount of eccentricity that was needed for the precise cyclical variation to the siderial motion. I wonder how he arrived at the amount of offset for the eccentric axis. Trial and error? Nah !!! 'Probably' by CAD motion testing.

Interesting to note that, if I consider the eccentric axis to be earth, the pin on the pin&slot gearing will represent the moon.

[u/internet-participant]

everything i wanna say about this guy has already been said. beyond exceptional in every single facet

[u/Tim_Buk2]

This is high tech primative technology.

[u/socialmammal0]

The fact that Chris has no formal training in machining, clock making, metalworking in general, CAD design, video production, filming, narrating or really anything he does on camera and yet does all of these things at a level that skilled, experienced professionals would be proud to put their stamp on is astounding.

That said the one thing I really want to hear is him narrating sex. "I'm using a downward stroke just at the edge of clitoris to start before moving in slightly higher pressure."

[u/50StatePiss]

Really hope a museum picks up the final Antikythera when he's done.

[u/[deleted]]

Anyone else impressed by that amazing carryover transition at 12:00?