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Begin restoration of zodiac precession, and year indication complications

We now turn to the restoration of two major complications within the tellurian. The first is the precession of the zodiac. This is depicted by the moveable lower silvered band engraved with the signs of the zodiac and surrounding the tellurian, first photo below. Pouvillon had described this in an interview for a Paris newspaper in 1953 and the function was also described by Mr. Bernard Miclet in his article published in the French antiquarian horological publication, Bulletin of A.N.C.A.H.A. Both of these sources were very specific about the existence and function of this complication in that the lower silver band rotated once in 25,806 years to mimic the zodiac precession and that Pouvillon achieved this through the use of “twelve wheels and twelve pinions”. This function has been referred to as 'the slowest hand in the celestial clock'. The upper silvered band is fixed and is marked in 360 degrees making the comparison between the two obvious. This upper graduated ring is also used to track the annual movement of the tellurian mechanism as it rotates with the Earth / Moon system allowing one to track the Sun’s apparent motion through the zodiac.

The second complication is the year indication which is displayed through an existing aperture in the enamel tellurian dial. That aperture was covered up when we received the clock. I will discuss this further when we begin the fabrication of that complication. The two complications are being described simultaneously because both are driven from a common source and so were built at the same time. 

As found, the zodiac ring was clearly mounted in such a way as to be moveable. The ring is held slightly loosely between three points, see arrow showing one of these points, second photo. However, all evidence of the mechanism to achieve the very long rotational zodiacal precession was missing. There were no wheels, no obvious mounting points for these wheels or plates where these mounting points could have been located. All we had were a few empty holes in the bottom of the tellurian dial support structure. The third photo shows one of these holes. So the question now becomes, was this complication ever built or did Pouvillon engage in a bit of puffery? Did Mr. Miclet really observe this complication in 1985 when he observed the clock for his article or did he simply take the information given in the interview for the Paris newspaper in 1953 as fact and repeat this in his article? We decided to reinstate this complication with the proviso that any work we performed was fully reversible with no alterations to the original artifact, a rule we have observed throughout the entire project. Also the complication would be made in such a way as to be invisible to anyone who had taken any of the photos we have up to this point so as to not conflict with the pictorial historical evidence we have to date. We also made sure that the complication conformed to the “twelve wheels and twelve pinions” asserted by Pouvillon. It turns out that this combination of wheels mathematically results in a surprisingly simple set of wheels using common tooth counts as follows with the first eight wheels being identical. Our initial drawing is shown using the formula below:

48 x 48 x 48 x 48 x 48 x 48 x 48 x 48 x 46 x 44 x 34 x 24
24 x 24 x 24 x 24 x 24 x 24 x 24 x 24 x 20 x 20 x 16 x 16
= 4128.96. The input ratchet mechanism divides this by four = 1032.24 for the input 18 leaved input pinion to the 450 toothed ring gear. That pinion turns 25 times for each complete turn of the ring gear giving 1032.24 x 25 = 25,806, the number of years for the ring gear and thus the zodiac ring to make one complete turn to indicate the precession of the Earth on its axis.

This is the first wheel design, using very small sized wheels in the train. One can see when the dial is placed upon the drawing the wheel train disappears. The same is true for the tellurian base. This design has the advantage of totally hiding the reduction portion of wheel train. Of course there are a few additional wheels that cannot be tucked under the dial, these feed the reduction train. By hiding the restoration to this extent we keep the look of the clock as much as possible to the way it was found.

On the other hand, if Pouvillon really did complete this system and used the 12 wheels as described, it is unlikely he would have purposely hidden them. The entire clock is designed to show off the wheels and their complexity. So we also explored this design using the same ratios but with larger wheel dimensions. These pictures show our second approach. Even with the larger wheels they are fairly hidden under the tellurian structure from above as shown in the second photo. Next a view from below the tellurian support ring. Although these show more than the first design, one must remember that the wheels are not actually sandwiched between the enamel dial and the lower extant spider support structure. The wheels will be mounted on an identical looking structure below the tellurian so when one looks directly from below the wheel train, no matter how designed, will be in full view.

The fabrication of the wheel train begins. First the they are scribed in the brass blank in a pattern to minimize waste. Next the initial drive wheel train wheels are cut and then the 30 wheels that make up this train, the complete train is 36 wheels, see schematic below. What is shown are actually wheels and their associated pinions. One might ask why the pinions are made of brass rather than conventional steel material and the answer is that this train moves so slowly that this is not a consideration. Another advantage to using brass in conjunction with the second design option employing the larger scale is that the pinions will also be spoked in addition to their mating wheels. The two outer rings of wheel blanks are used for the zodiac precession. The center wheels are involved with delivering the drive to that large reduction wheel set and are also used for an additional complication, the year indicator, to be discussed later.

We now begin to fabricate the ring gear that will drive the zodiac band. The ring will have 450 internally cut teeth and is relatively thin. Considering this, the material must first be annealed to relieve the natural stresses that are present in all modern rolled brass. The raw metal stock is heated in a furnace and then slowly cooled. If this is not done the ring will distort under the machining process. After the ring is finished, it will be re-hardened. Next the disk is cut from the brass stock. Normally the round portion is what is used for a conventional wheel and the surrounding material disposed of, but here the reverse is true.

The blank is quite thick, about ” or 6.2mm. However, Buchanan will not use the entire thickness for the teeth. The finish form of the ring requires a recess which can just be seen above and below the cutter in the second photo. The actual tooth thickness is more on the order of 2mm. Next is a close up of the cutting tool used to make the interior teeth. It is the same used for the epicyclical fly fans on the commission astronomical clock, also see video below to see the cutting tool in action.

First photo shows the two blanks for the zodiac precession and year indicator gear rings with their fine teeth. Each one has 450 internally cut teeth. The outer portions of the square blank is next trimmed and the next photo shows the ring attached to a plastic disc. That disc is what is attached to the lathe chuck. This is necessary because the ring itself is too delicate to be directly gripped by the chuck.


The ring's shape is further refined. The next two photos show the snug fit between the toothed drive ring and the zodiac band. That ring will be flush with the lower edge of the zodiac band, remaining unseen from the outside.

I now turn to the year indication complication. The tellurian dial originally had a square aperture in the January sector which indicated the year using the last two digits. We have ample photographic data of an identical tellurian dial that shows this. The original tellurian dial as well as many of the tellurian components was not created by Pouvillon. We have evidence that the dial was made about 1790 from another, identical example and it had a removable second digit to make the dial useable when the century turned from the 1700’s to the 1800’s and so needed to have the second digit in the year changeable from ‘7’ to 8’. The Dial has the first digit of the year permanently fired onto the surface just like in our example. The second digit was removable with the remaining two visible through the aperture indicating 00-99.


As received the aperture on the dial was closed with a white filler material. Here we begin to get into some pure speculation. On the one hand Pouvillon was anxious to have as many complications as could pack into his clock. Furthermore this indication was not repeated anywhere else within the movement and if Pouvillon received the tellurian structure intact, it should have had this complication already present and ready to go. He would have had every incentive to use it. On the other hand, what if the tellurian was not complete and presume that the year date ring and maybe the associated driver were missing? In this case Pouvillon may have taken the easy way out and simply dispensed with the effort to recreate this complication and covered up the aperture. We do know after the fact that creating this ring took quite a bit of time and skill; surely Pouvillon had the skills but we do not know if he actually did it. Of course a third alternative could be that this complication was lost as were many other parts during events after Mr. Pouvillon’s passing and as a result the aperture was then closed up.

The first two photos show the date ring laying on the underside of the tellurian dial. The dates will show through an aperture on that dial which we now have opened after removal of the white plug.

The first two photos show the date ring rollers. These are positioned upon the three existing brass pillars, last photo. These pillars are also used hold the tellurian dial feet. The rollers simply slide over the existing pillars.

Numbers are temporarily penciled on the ring perimeter to check for legibility under the existing enamel aperture. Furthermore they must be placed in exactly the right position since the ring will be advanced annually in a single 'jump', so that number must appear correctly under the dial aperture at the moment the ring is advanced as it will remain there for the rest of the year. The next photo shows the year ring gear behind the tellurian dial. When seen from straight on it is just at the inner edge of the dial. Next are the two ring gears as seen from below. The outer one drives the zodiac precession and is attached to the zodiac silvered band while the inner one rides on the rollers just below the enamel dial and will show the year within that dial's aperture.


Here we see both ring gears neatly sandwiched within the tellurian structure. Buchanan commented that the precession of the zodiac is so slow, that in the time left within our lifetimes, say 30 to 35 years that the zodiac ring would have moved 1/10th of a millimeter, the width of a fine pencil line. Of course one will be able to advance the step lever drive to see the date ring advance one full revolution, that is one century, with each 100 clicks and so we should be able to then see the ring move, particularly because it is adjacent to the 3600 calibration ring above it.

Now we see the round plate upon which all of the zodiac precession as well as the year date ring mechanism will be mounted. This will later be trimmed to the same design as the four spoked frame which currently serves as the base for the tellurian. The wheel with the large hole in the center will fit upon the steel flange shown in the next photo. Next is a close up of the flange; it screws into the base plate and one can just see the threads cut into that plate.

 Next the wheel is mounted onto the flange. The flange is now screwed into the plate securing the wheel in place, yet still acting as a bush upon which the wheel is free to turn. The entire reason for this design is the fact that we needed a wheel to revolve right at the axis point of where all of the orrery’s planet drive tubes intersect through this hole. The last photo shows the final machining of the zodiac gear ring, now having an ‘L’ shaped profile.

Buchanan now makes a ‘containment vessel’ from steel wire to hold a steel pinion assembly during the hardening process. In the second photo he demonstrates how this is fired. Next the pinion as it was removed from the coil and is now properly hardened.

Next two photos show a second pinion which is fixed upon the same arbor. Afterward the pinions are mounted in place where the lower pinion receives the drive and transfers it to the upper pinion which meshes to the zodiac ring gear.

The first photo shows the pinion edge on. It passes through an open area in the original Pouvillon orrery support plate which is shown sandwiched to the new plate via the original pillars supports. Remember that these same pillar supports are also used for the rollers that hold the year indication ring. The photo actually obscures the lower pinion upon which the upper pinion, shown, is mounted. Next we see the drilling operations to secure the wheels to the plate for the ring drive.

Here we see the wheels secured into place. Next is a close up of the wheel collets which are made to look like those from Pouvillon’s original wheels as illustrated in the third photo. See video below to view these wheels in motion.

The first photo shows a brass bush that is inserted between these two wheels as they need to freely rotate past each other. The following photos shows the entire wheel set needed to drive both the zodiac precession and the year date ring.

Now we begin to fabricate the feed mechanism needed to drive both the zodiac precession ring and the year date ring. This will be accomplished by a ratchet feed triggered by the arm of the innermost planet Mercury. We had to choose this planet as it is the one at the top of the orrery planet stack and is therefore closest to the mechanism needed to trigger the zodiac and year rings. The first photo shows the initial rough components. The next photo shows an interesting design. The lower cylindrical structure mounted to the base plate is a bearing that fits into the upper gear above. This is necessitated because the other end of the arbor shown here is attached to a ratchet drive wheel. The width of the plate is too narrow to accommodate the lateral stresses associated with the ratchet assembly. In the last photo we see the wheel, far left, fully inserted upon the base bush.

The first photo shows the initial rough ratchet feed pawl. Next we see a first refinement of the feed pawl. The pawl is next mounted and showing the positioning of the feed pawl spring.


The first photo is an overhead view of the tellurian showing the original spider structure sandwiched to the new, and as yet unfinished, plate as well as the year date ring on its rollers. If one looks carefully one can see the ends of the arbors which carry all of the wheels shown in the next photo. Next we see the flip side all of the thirty wheels are now in place, functional and ready to be spoked out. Also one can see the ratchet arm extended over the impulse wheel. The ratchet itself is tripped by the small pin on the large wheel just below the lever. That wheel is in turn driven by the center wheel which turns on a bush surrounding the exiting orrery support tubes. Later a bracket will be mounted to this wheel which will engage the support arm which drives the planet Mercury, thus providing the drive for these two complications.

This is how we are able to get the needed drive that exists below the orrery ring and tellurian base up to the zodiacal ring shown here as the outer brass rim. The impulse wheel, in turn gets a drive above the ring and dial support structure to the date ring above. The reason we use a ratchet instead of a steady gear drive is that the year ring needs to be moved in discrete increments so that once per year the date will flip over completely and be properly displayed within the viewing aperture at all times. Since the zodiac precession wheel train’s ultimate output is one revolution every 25,806 years it makes no difference as to how this train is driven.

Shown here is a schematic of the gear train layout for the zodiac precession as well as the year date complications. There is a total, including the output rings, of 36 toothed wheels



                                                                                                                  Pouvillon-March-2012-1.mpg   Astro_04-08_vid_2.mpg

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