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Complete restoration of zodiac precession, and year indication complications

 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 orrery.

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 above.

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 historical photographs.


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. Next the jig is now assembled and the next photo shows it in place; bolted onto the index head.

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 dividing head.

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 brackets.


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 supporting structure. 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.

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