G'day Chris here, and welcome back to Clickspring. In this video I make the gearing and support
structure required for the eclipse prediction train of the mechanism. Despite the fact that a solar eclipse is a
reasonably common event, they do tend to be fairly localised. So most of us rarely get to see more than
one or two over a lifetime. The result is that even though we have a complete
understanding of what's going on, the passage of totality over the surface of
the earth retains its power to completely captivate
our attention. It is to say the least, a profound experience. And it was perhaps even more so in the Ancient
World. Across many cultures, Eclipses, both lunar
and solar were believed to be omens of great significance. Foretelling the imminent death of a ruler, the outcome of a military campaign. Or on occasion just providing a good excuse
to justify a particular course of action. Little wonder then that the Ancients chose
to include an eclipse prediction function when constructing their all encompassing model
of the Cosmos. At the heart of the eclipse prediction method
used, is what we call The Saros Cycle. Yet another fortunate cosmic coincidence, where 223 lunar months after a given eclipse, a nearly identical eclipse will occur. This leads to what's known as a Saros series, where over a period of well over a thousand
years, roughly 70 to 80 eclipses, will follow one
after the other in sequence, separated by the regular interval of 223 lunar
months. The observation of any single eclipse from
a given Saros Series, is all that's required to identify the date
and the time of all subsequent eclipses within that series, and so makes possible
accurate eclipse prediction. Now the Saros dial carried the markings for
a large proportion of the eclipse series that were active during
the period of the mechanisms construction. I'll cover this in more detail when I engrave
the dial in a later video. But essentially all the user needed to do
to predict an eclipse possibility, was to crank the mechanism forward until the
Saros pointer reached one of the marked cells. The inscription indicated whether the eclipse
was solar or lunar, as well as the nominal time of day that it
was to occur. And the month of the eclipse was simultaneously
indicted on the Metonic dial. Now since a lunar eclipse can only happen
at full moon and a solar eclipse at new moon, the day of the eclipse could be easily identified. By simply noting the day that the required
lunar phase was to occur, or by cranking the mechanism forward and using
the front dial to observe the day of alignment. So Ignoring sign convention, and viewed from
the perspective of the pointers, the Saros gearing calculation can be represented
as follows. Again, you'll notice that the 53 tooth gear
is cancelled out, and with simplification, the expression can
be reduced to the following. Which presents the behaviour of this part
of the mechanism in a very intuitive way. Because, you'll recall from the previous episode that the Metonic cycle is 235 lunar months
in 19 years. So 19/235 is just another way of saying "one
lunar month". We need 223 of these months to represent the
Saros cycle, and we'd like them to be divided over a 4
turn dial. A slightly less intuitive way of presenting
it is as the number of days. But this does highlight one of the defining
characteristics of the Saros cycle: And that is that its not a whole integer number
of days. That 1/3rd of a day remainder, has an effect
in particular on the location of the repeating solar eclipses. The earth of course continues to rotate for
that additional 8 hours, and so the location of the repeat eclipse
is shifted about 1/3rd of the way around the Earth. After 3 appearances, its back very close to
the original location. Which brings us to the Exeligmos pointer. Its role is to indicate this 8 hour time shift
information, advising the user to add either 0, 8 or 16
hours to the nominal eclipse time. And again the gearing calculation can be simplified
to something that shows exactly what's going on. We see 223 lunar months, the Saros period,
multiplied by 3. Or as its otherwise known, The Triple Saros. So where exactly did this deep astronomical
knowledge come from? Well essentially from direct observation of
the night sky. It turns out that the Saros cycle, and in fact much of the other astronomical
knowledge underpinning the mechanism was known to the Babylonians for a very long
time prior to the mechanisms construction. Clay tablets from the period suggest a culture
that were serious watchers of the night sky. With continuous detailed observations, that
spanned generations. These observations were used to develop sophisticated
predictive models, and much of the research supports the idea
that at least some of this knowledge made its way into Ancient Greek culture. So the astronomical heritage of the mechanism
is relatively well understood. But we know much less about its engineering
heritage, or the workshop tradition that enabled its
creation. Currently, the best source of information
is the device itself. Because its features directly imply the existence
of certain tool technology. Now the exact nature of that technology is
the big question, and we may never know for sure. But we can certainly try a few things out
and see what might have been the case. So with that in mind, its time to open up
a hole position that I marked back in episode 2. This is the pivot location of the E assembly,
and its a perfect opportunity to make the very first hole in the mechanism
using some of that ancient tool tech: The Pump Drill. I'll be adding a considerable amount of gearing
under the E assembly in a later episode, that essentially supports it. But in the meantime I need a temporary support
and this bearing will do the job. For this part of the train there are 5 wheel
assemblies to make, as well as their supporting structures. Starting with the E assembly, the scans show that the ring gear was fastened
in place using rectangular pierced lugs and styled cotter pins. Most of the mechanism uses simple tapered
pins fastening, so this is different, and certainly gives
this assembly a distinctive character. Its important when installing the lugs that
the wheel alignment be maintained throughout the process. So to help with that, I used the small jig
that served a similar purpose when making the main solar drive wheel B1. With a simple bushing installed, it can now
serve in a similar role as a drilling platform for opening up the
holes for the lugs, and also as an alignment tool during the fitting
process. That first hole serves as a convenient drilling
guide for the hole that'll receive the lug. I turned the lugs to be a light interference
fit in the holes, so a gentle tap with a hammer was enough to
seat them tightly home in preparation for peening. Ok, so with the first lug in place, the next
step was to open up the matching rectangular hole, so that the wheel can slide into position
over the lug. The alignment jig now becomes essential, making it possible to progress through the
fitting process for all 4 lugs, whilst being quite sure that the wheel alignment
is being accurately maintained throughout. The cotter pins were then brought to a close
fit with the lugs and pushed firmly into place. OK, so with the E assembly complete for now,
I moved on to the F assembly. Which unlike most of the wheel assemblies
made so far, rotates on a post support structure. The wheel assembly consists of 2 wheels that
are permanently staked onto a square hub. Requiring the formation of the hub, as well
as the opening up of the wheels to match the square. Off camera I turned up the post and riser
that make up the supporting structure for this assembly. Its a simple disc spacer, and a post that
passes through the main plate to be fastened with a pin and washer on the
other side. Next up is the bearing for the Saros pointer, which is yet another composite structure consisting
of a rectangular block body and a separate spacer flange. The Saros arbor was formed with a very light
taper to ensure that the wheels were a firm, well registered fit. And the pivot sections turned to be a close
running fit in the bearing. Now Its helpful to consider the H and I assemblies
together, since they share this most unusual pivot block
as a common support structure. The arbor for the Exeligmos assembly was constructed
in the usual way, but I made a temporary and quite short version
of the H arbor to allow for a specific depthing technique
that I'll show in a moment. What I call the HI Pivot block is an unusual
little idea, that will eventually require a small clearance
notch to be removed in a later episode. In fact it'll remain loose in the mechanism
until I can cut that notch. For now though, its enough to simply depth
and plant the 2 assemblies in a suitable place on its surface, and form
the basic profile. The main plate was then opened up, and the
square bearing hole formed. These two positions are essentially absolute
locations, governed by the dial artwork. And depthing could have been conducted from
these positions before filing out this square hole. But at the risk of the position almost certainly
moving as the square was formed, and so compromising the depth. So its worth pointing out that the Makers
choice of putting the F assembly on a post, rather than an arbor, permits the use of a
very simple and practical depthing tool. This means that depthing can be left until
after the square bearing has been fitted, and so any position error can be accommodated
without issue. The temporary version of the H arbor, means
the HI pivot block can be used in a similar manner. A small pin ensures that it pivots from the
Exeligmos position, and the block can then sweep over the surface
of the main plate, to find the correct depth of engagement for
the H assembly. Again removing the risk of the Saros pointer
bearing being poorly positioned when filing the square. Now of course the very compact nature of the
machine means that vertical clearances also need to
be accurately set. I mentioned in Episode 3 that I think the
composite structure of the assemblies, and in particular the use of spacer components, was the secret to achieving the incredibly
close clearances implied in the wreckage. And here's a perfect example of what I mean. The height of the saros pointer assembly is
set by the height of the bearing in which it sits, and that height can be easily set by this
little spacer. I originally made it slightly oversized, but its a straight forward job to set a clearance
of just a few hundredths of a millimeter, by simply abrading the spacer until the barest
daylight remains between the adjacent assemblies No special tools, or absolute measurement
are required. Just keen eyesight, and a flat abrasive surface. The entire mechanism could have been set to
very close clearances using this simple trial and fit method, and I'll continue to use it as I move forward
with the build. Ok, so with the depthing and clearances set,
the temporary H arbor was removed, and replaced with the permanent full length
version. This arbor threads up from underneath the
plate, and so requires that a fastening pin be positioned
just above the wheel and pinion. And I used the bit component of the pump drill
on its to form the hole. It is much slower than using the driving mechanism, but using it by hand gives greater control
over the hole position. The other assemblies were pinned using the
same technique, and with that complete, its time to put it
all together and see how it performs. In the next video I'll make a start on one
of the more remarkable sections of the mechanism: The gearing that models the lunar orbit. Thanks for watching, I'll see you later.
I fell asleep twice in the middle of the day watching this. Something about his voice soothes the soul.
The definition of artisan. Love me some Clickspring, dude is insanely talented at his craft and at making content.
So in the last few days we've had Clickspring, Primitive Technology, AND Project Binky.
Just need Frank Howarth and Sorastro to release new material to make my month complete.
These sure take a long time to come out, but man are they a satisfying watch.
Yess Iโve been waiting for the next upload
damn, he makes that stuff fit so tight... what a craftsman
A pleasure as always, although I have no idea what is going on most of the time.
The amount of patience and care on display in Chris's videos is unreal.
I cannot fathom how he makes those tiny metal things fit so perfectly, by hand