POUVILLON RESTORATION PROJECT - April 2012
Complete restoration of zodiac precession, and year
In this section we complete the restoration of
the zodiac precession and the year indication complications.
I had concerns if
Buchanan had considered how the drive for the zodiac precession will deal
with the fact that the orrery will be able to be demonstrated in reverse.
This is an issue as the drive for this as well as the year indicator ring is
driven from the arm that holds Mercury. So what happens when Mercury is
rotated in reverse? The first photo above shows a bypass clutch devised to
deal with this eventuality.
As with the need to account for reversal of the drive discussed for the
zodiac precession, I asked Deryck to provide for the ability for one to be
able to manually adjust the yearly date ring. This is not only needed for
the initial set up, but also in the case that one trips the ring forward or
reverse if demonstrating the tellurian near the end or beginning of the year
when the ring would normally be near the time of actuation. These photos
show the wheel set that will drive the small steel pinion which meshes to
the date ring gear. Notice the spring washer under the second wheel.
The center wheel arbor
is now fitted with a key-square which will be used to make the adjustment to
the year indication ring. The spring washer shown previously is under this
wheel. When one wants to adjust the ring the key is placed over the square
and depressed. This pushes the wheel out of mesh with the far right drive
wheel, but still in mesh with the pinion connected to the ring. The next
photo shows the position of this adjustment square within the existing
tellurian structure. It is nearly opposite from the existing adjusting
square Pouvillon used to move the thirteen indication pointers for the
various movable feasts of Easter and is of the same key size.
Here we have the main
frame cut out which will hold all of the wheel work for the year and zodiac
precession complications. It is designed to be as hidden as much as possible
within the existing tellurian superstructure. In fact the two are
superimposed in these photos. The first shows the new structure over the
original, and the second the mechanism flipped over to show Pouvillon’s
structure over the new. This was purposefully designed to make the new
restoration of these functions as unobtrusive as possible.
These third photo as
well as the first one below are close ups of what is shown below and above
the plane of the tellurian base and with the inclusion of the main drive
wheel which is located at the center. The two pairs of holes drilled at the
2 and 7 o’clock positions will hold the brackets that will contact the arms
upon which the planet Mars is attached on the orrery. It is this planet’s
rotation that provides the drive for the two complications. We had to choose
Mars as it is the top of the collet-nest that provides the attachment points
for all of the planets outside the orbit of Earth as represented in the
The last two photos show
the laborious process of cutting out all of the wheel spokes. There are 18
individual wheels. However, on 13 of those wheels, the pinions are not the
solid, conventional form, but an additional spoked wheel. So in reality
there are 31 wheels to be spoked for the two restored complications. These
wheels are too small to be held by hand and so are held in a jig on the bed
of the jeweler’s fret saw, last two photos
Here we see the initial
few wheels completed. The first photo shows a view from the side showing the
new plate and the second from the side showing Pouvillon’s tellurian support
plate. The two are nearly perfectly superimposed.
Next a view from
The wheel spoking
process continues in these photos.
The first two photos show the completed wheel works.
The third photo shows the completed two complications which fit completely
within the existing tellurian structure.
From the three-quarter side view they are nearly impossible to see. We see
to it that our restoration will still be in keeping with the known
Even from the top, most
of the new wheel works are hidden.
The next job is the engraving of the year indications on the ring. The first
photo shows Deryck’s trial numbers to test for both size and position. The
next two show the numbers within the existing aperture on the tellurian
dial. Originally the dial would have had a removable number after the
enameled ‘1’, this would have
been a seven since there is another example of this tellurian with just such
a removable figure. The tellurian was created in the 1780’s and so would
have needed a changeable second digit to update the dial for the next
century. I asked Deryck to introduce some slight variations in the
positioning of the numbers in keeping with the rest of this as well as other
dials. We will, of course put in a nine after the current first digit as
would have Pouvillon
Before engraving can
begin, the ring must be indexed for 100 positions of a century, each must
have the two digit number correctly centered within the tiny dial aperture.
Deryck is using his numerically controlled dividing head, rather than
manually dividing the ring sectors due to the large number of divisions.
However, just to be sure he first scribed the left and right edges of the
dial aperture on the ring for each of the 100 positions as they click into
place as double check to the index. Of course for all of this to work, all
of the wheel works, and especially the feed ratchet, must be near perfect
for the entire system to work properly. The next photo shows the jig used to
hold the ring in position on the indexing head. All of this is custom made
for just this one ring.
jig is now assembled and the next photo shows it in place; bolted onto the
Just above the ring is
the engraving head of the pantograph engraving machine, first photo.
Next we see an overview of the pantograph
machine. The third photo is a close up of the letter-tray containing the
number masters. That tray can be seen behind the upper arm of the machine
holding the blue numerical index controller in the prior photo. That
controller is attached to the stepper motor which is attached to the
dividing head assembly, (the silver rectangular device). The entire indexing
system is attached to the bed of the pantograph machine. What we have here
is a combination of two machine tools to achieve an unconventional result.
Normally, a pantograph is used to create conventionally configured script
which is linear. In this case we need to engrave in a circular and very
accurate pattern, hence the need for this unconventional setup using the
The first photo shows the follower pin of the pantograph which will trace
the numbers in the brass masters. Next is a close up of the completed ring;
highlighting the ‘51’ which is
just a bit out of alignment in keeping with the rest of the work on the
clock. The last photo shows, however, that taken in context the
numbers are all quite closely aligned and all well within parameters to
correctly display within the tellurian dial aperture. The last step is the
silvering of the ring surface and then blackening of the numbers for
contrast. Think of the complex machining it took just to create this one
part, the stepped ring, the 450 internal teeth and the circular engraving.
The first photo shows
the pair of slotted angle brackets or ‘dogs’ attached to the center input
drive wheel which in turn powers the zodiac precession and annual year
indications. The next two have the rotating collet ring to which the planet
Mars is attached via the wire shown positioned near one of the slotted
The center wheel
complete with brackets mounted in place.
The drive assembly is complete with both the
Mars planet attachment rod and its opposite planetary sign rod positioned
within the slots, see circled areas, second photo. It is this planet at the
top of the collet nest which is the input power to drive the center wheel
for our two complications. The wheels needed for these complications are
located below the tellurian deck which precluded the option of getting the
power feed from what would otherwise be the obvious point, the tellurian
rotating boom which rotates at once per year, but is above the dial and its
The last photo is an enlargement of an old photo
from the 1950's of the movement. The circled area appears to show some kind
of structure below the tellurian rings and could very well be a similar
bracket dog to deliver the power for the zodiac precession in the same
manner as we have.
The entire mechanical
restoration of the year indication and zodiac precession is now complete.
The toothed ring that drives the lower silvered zodiac band is machined to
such accuracy that it can be held by the zodiac band by friction fit. The
view from ‘below the deck’ of the tellurian assembly is stunning. Compare
this to a similar view of the same area of the tellurian as received.
There is a large empty space where all of the components neatly fitted into.
On the other hand, the
restored components are hidden from a side or nearly any other view one
might have of the clock. One needs to look carefully and deliberately to see
any of the components. The exception, of course is the fact that now we have
a functioning year indicator operating in the place where before we had a
blocked dial aperture.