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Planisphere mask, finish bezels and misc. demonstration mechanics  - October 2020

This month Buchanan creates the planisphere mask. This marks a milestone since this is the last mockup component, other than the dial hands, to be fabricated into metal.


The first illustration is the CAD graphic for the computer-controlled mill that will create the planisphere mask. Here is an application where a one-off part still makes sense for the time it takes to program the machine because of the complexity of the part. The engine-tuning and net as well as the engraving all contribute to this. The next photo shows a test run of the inscription.

I can't remember exactly when I had decided to have this Latin inscription added to the clock, but I had first seen it in a small pamphlet written about the astronomical clock in Strasbourg, France by Jean-Baptiste Schwilgué, in 1843. I had purchased the pamphlet sometime in 2006. The design for the Sun & Moon rise-set module was begun in late 2016 and at that time it was decided to use the unique variable differentials used in the Strasbourg clock for the Moon's orbital anomalies. It may have been at that time that I began to look into my reference material on the clock.

The phrase was part of an epic poem, Metamorphosis, written by Publius Ovidius Naso, commonly referred to as Ovid in AD 8 and is translated as: To man God gave an upwards gaze, bidding him to behold the sky, and raise his erect countenance towards the stars.  When taken in the context of the poem it is when God separates Man from the animals by giving him the ability to stand erect and gaze toward the heavens, presumably to unite him with God in contrast with the downward earthly gaze of animals. Obviously Ovid was not familiar with primates! But given when he lived and that he was from Greece that’s understandable. The font chosen was Century Gothic seen in MS Word.

I thought this to be appropriate as the planisphere represents the night sky with the stars that Man would observe in the poem. In fact the entire machine is a small encapsulation of God's creation as experienced by Man at several magnitudes. There are the stars as seen from the ground represented by the planisphere, then the Moon and Sun within the tellurion and the Sun & Moon rise-set module above it, and finally the Earth's neighborhood as represented by the orrery that crowns the machine.

Begin the planisphere mask


The planisphere mask is now started. The mockup model is fabricated of Corian and spray painted a gold color, on the left, and was seen in the May 2018 installment, and has the distinction of being the last mockup piece to be made into its final metal incarnation.


In the first photo we see the beginnings outline of the planisphere longitude and latitude net. Next the net begins to appear as the cutter pierces below the back side surface.


Now the lower area is being prepared for the diamond engine-turned pattern. Next a detail of the net.

A close up of the diamond pattern engine turning similar to that seen on Breguet's watch dials.

The planisphere mask is now fabricated from the mill and is ready for final hand finishing. Doesn't look like it needs it does it?


The first photo shows the silver sector dial being engraved. Next the dial is engraved and black dial wax filled into the lettering.


Buchanan explains: Today I finished the ring for behind the mask. I started with a bent up and silver soldered ring glued to a face plate, first photo. Then I parted the ring from the face plate photo, second photo. This gives a perfect cut to the side that was glued to the lathe's faceplate.


I had to machine a locating groove in the back of the mask, third photo. And a matching raised locating ridge in the cylinder photo, fourth photo.

The mask and the ring will be held together through a flange created by milling the rest of the interior surface of the ring. This is the reason the original ring was made from a thick material.



These four photos show the drilling and tapping of holes for the screws to secure the mask to its ring.


Buchanan explains: Progress on the mask today. First photo, machining the outside to size. Second photo, machining the curve on the inside of the upper moulding.


Third photo is the embryo upper cornice. The inner section is milled to conform to the cylindrical portion of the mask. Then the gap is filled with’ body filler or Bog’ as it is known here before cutting the rear profile to match the main clock base Next, cutting the recess for the movement.


Fifth photo, getting there. And last, drilling the fixing screw holes.


The first photo shows the fly cutter machining away the back profile of the ring's decorative molding piece to match the main base's upper cornice of the clock, it also had to be mounted in a groove, yellow arrow, and clamped down inside a channel, red arrow, to stop it falling apart under the cutting loads. There is not one square flat face that can be used for proper clamping. Next photo the planisphere main support is dowel pinned to the base frame to preserve alignment, yellow arrows.


First photo is the trial fitting on the clock. Super glue holding the intermediate plinth in place so that it can find the correct screw position. Next Buchanan screwed the intermediate plinth to the base prior to final alignment and pinning. This is all necessary to keep the adjustment pinion in mesh which will be mounted on the mask.


The first photo shows the final molding, one can see there is no proper reference face to hold it with when machining, see fourth photo prior. The next steps are to trim the upper cylindrical section of the mask to clear all the gears behind it and also the whips of the Fasoldt flies. Then the final polishing of the mask and the web.


Buchanan writes: First photo, for once things work out well. The scroll saw can fit inside the mask. Next, the start of hand fitting the mask to the base. Measurements and scribe lines help but it is just cut and try in the end.


Next two photos, getting there and then extra-long counter bore so that the screw heads will be recessed to make final assembly possible.


Buchanan writes: I have measured and drawn the spacing of the demo select lever. We have 19 degrees of movement between each selection position or an inch and 1/8 spacing on the rim. I made a paper mock up and took some photos, (above and below). Please remember that there is also a cut out for the setting window and we only have an inch for the script. I am racking my brain for an elegant way to fit a pointer though. I think it is the correct place for the demo plaques though. The second photo shows the Corian mockup that has the star field calendar setting window cut out behind the three paper mockup windows.

The three tags represent the selector for the demonstration function. The first is when the machine is in normal operation CLOCK DRIVEN, next when all of the celestial modules are being driven together, CELESTIAL DEMONSTRATION, next when only the orrery is being driven in high speed (12 times the speed of the prior demonstration), ORRERY DEMONSTRATION. The window behind the three mockup tags is the setting calendar dial for the star field and is already designed and cannot be altered.


The same three mockup tags on the fabricated planisphere in the first photo, note the star field calendar setting window has not yet been cut. The second photo shows the solution that was adopted.

Buchanan could not put the selector tags on the rim of the planisphere's body, there were obstructions that could not be surmounted and so the proposal is to have a sector dial behind the planisphere, on the same plane as the spring duration dials. This, however has also proved impossible, so it is one issue yet to be resolved. Perhaps a small semicircular sector dial can be placed above the square  selector keyway with the letters C, D and O for Clock driven, Demonstration, and Orrery. In this way someone who is unfamiliar with the mechanism will know immediately that this is a selector and not a conventional winding square meant to be cranked all the way around.


The first photo shows where the original setup of the Sun setting clutch was. This would allow the user to move the sun hand around by manually grasping the sun arbor. The problem is that this was made without taking into account the net that now covers the area where the sun can be see and so makes it impossible to set it in this way. The second photo shows the two wheels that are positioned directly above the planisphere. Here is an instance where Buchanan's ingenuity, and serendipity came into play.   


In this photo we see the new Sun setting arrangement, yellow circle. The knurl knob, clutch and the new wheel arrangement is seen in the second photo above this one are now assembled above the planisphere setting window. Buchanan just needed to split the arbor that the two wheels were fixed to and put the clutch between them. Now when one turns the knob the Sun moves, but when left alone, the wheel directly behind and clutched to the new wheel will drive the Sun in normal clock time mode. The second knob, white circle, adjusts the planisphere star dial and is set through the window aperture.

The longitude and latitude net is now hand finished


Buchanan explains: Because the web is so delicate I had to make a backing support plate. Fortunately I had the machine code that I could slightly modify. I also made a secondary plate with a recess so that I could spin the support plate on and it is always over a hole.


We now turn to the refinement of the mask net. Look carefully at the photo, while the net is very nice, it has a flat top and side profiles. Here is where Buchananization begins, to take something that is good and make it great. The mask net is placed over a substrate made of Corian to the exact outline to support the net for the hand finishing to be done.

The net before the hand finishing is fitted over the support substrate. Note the straight, blocky profiles of the webbing.


In the first photo Buchanan uses a set of calipers to show that about 50% of the mass of the web is reduced. Both the vertical sides are reduced by tapering these toward the top. The remaining part on the top that is flat is given a rounded profile.

The last two photos above show the difference between the ‘before and after’ effects of the hand profiling. The photos show on the left the finished web compared to the unfinished on the right; and the corresponding reduction in the thread profile.

Buchanan writes: There are 4 rings of 16 holes = 64 holes in the web. Each hole has 4 sides = 256 sides. Each side has a top, bevel and side to polish. Total of 1024 facets, and 256 bevelled corners. If I can finish a facet in one minute it comes to 17 hours. And I have just started.

It is this type of attention to detail that makes the clock so special.


The mask is truly a stunning asset to the machine. The grid is so delicate and reflects the light beautifully. Where they intersect is lovely. Even up close under magnification the millwork is perfect, Breguet would be proud! The Latin inscription is nicely proportioned and lends a bit of mystery. The tiny screws holding it are so fine as to be just about invisible.

The completed planisphere mask. It should be noted that the dial itself is still a paper photocopy mockup, the enamel dial will be installed only when the entire module is finished.


Two three-quarter views of the planisphere installed on the clock.

Front elevation of planisphere module.

The entire compliment of enamel dialing with their bezels completed.


Compliment of bezels now ready for gold plating. Another refinement to the clock.

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