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Orrery, central support pillar, dial support bracket, begin Saturn gearbox - July 2018

This month Buchanan begins construction of the last mechanical system, the orrery.



The last three photos show the output wheel of the orrery drive with its ivy shaped frame; part of the orrery two-speed transmission drive completed in November of 2013. Note the square arbor. This will be keyed into the female square in the short brass tube just below and that is attached to the drive rod for the orrery allowing it to be easily parted from the rest of the machine for transport or servicing.

Buchanan writes: Here is the start of the orrery.

I have the centre square drive adapter to the input arbour and the main orrery pivot roughed out. The big block of brass is the start of the main 3 dimensional bracket the morphs? from the  centre main clock plate to the main orrery support. This will be part of a quick release clamp that allows removal of the orrery from the clock. I can see the orrery will be in and out of the clock a lot until the dial is mounted and Saturn is fitted. After that we will be free from external references. It will be placed there many more times to see what it looks like as work progresses.

Next will be the dial arm support combined with the centre main column. This is also a complex 3 dimensional part  with the 4 dial arm attachment points. It is also very prominent in the clock and there is a conflict between complexity and looking too heavy.


This is the start of the main bracket that is fixed to the clock that will hold the orrery.


The third photo shows the bracket being cut to its rough ‘L’ shaped profile. Next the bracket is mounted to the lathe to cut the decorative contour on the collar.


In the first photo the bracket is seen to the right of the extant drive frame and in the next photo joined to the frame. Note the use of locating pins. These are used whenever two frame parts are joined.

The turned collar is now complete. The bracket is mechanically finished apart from the quick-release mechanism.



Now begins the main armature which holds the center orrery arbor and the four arms that will secure the large, horizontally-mounted dial.


In the first photo one can see the mounting holes on four quadrants to which the orrery dial support arms will be attached. The central orrery arbor is seen running through the armature and directly through the mounting bracket to connect with the drive wheels. Buchanan writes: I am working on the dial support arms. I have enclosed a scan which you might find interesting. Second photo.

When looking at the clock from the front (more apparent in real life) two features stand out in relation to the orrery dial support arms: The two Robyn  sprockets because of their visual density and proximity to the orrery support, and, the two escapement antifriction wheels , because of their movement. As you can see, our supports for the orrery dial tend to follow the shape set by these four wheels. I want to make sure that the frame design compliments this shape match to maximise the visual effect and give the impression that the Robyn sprockets were matched to the dial support arms.

What is shown in the second photo is the original wood mockup bracket for the orrery dial so it is not complimentary to the elements we are discussing. What Buchanan wants to do is to design the actual bracket to compliment the Robin remontoire wheels as well as the antifriction wheel pair as shown by the yellow circles.


Buchanan now composes the dial support pieces into the CAD-CAM machinery. This is one of the few examples where computer aided design is used in this project. The reason is because there are multiple identical parts. The first photo shows the computer screen overlaid with a clear Mylar sheet that has the hand-drawn bracket design. The computer diagram is them manipulated until it matches the original design and the result is shown in the next photo.


The design is now carried out by the computerized mill. The first photo shows a bracket. The second photo shows the identical dial support arms and brackets.

The brass blank is shown with the completed parts from the mill before being parted from the sheet for final finishing.



The first photo shows the bracket parts after finishing to assemble the cross armature that will support the largest dial in the clock, the orrery dial ring, which is 11 3/8” (29 cm) in diameter. The second photo shows the decorative support brackets for the armature. The next two photos show close ups of the support structure. The central tube also serves as the support for the orrery.

The completed dial / orrery support structure.


The dial is shown on the support structure. The next photo shows a portion of the design diagram from the German language book on Hahn’s orrery. Buchanan writes: If you look at the photo there are two gears of 103 and 104 teeth on the orrery centre. The 103 tooth gear is fixed stationary to the centre, as Jupiter revolves around the centre, it ‘walks’ the double gear 68/41 teeth around the 103 tooth wheel and this provides the drive to Saturn’s arm via the 104 tooth gear attached to Saturn’s hub. This is rather like the Fergusons paradox that you like. Now as you see in the diagram, these 4 wheels are rather small. I would like to increase their diameter to at least double, as they project into dead area the opposite side to Jupiter. As long as they clear Saturn they can be as big as we can fit in. What do you think? It may make the clock look a little busy, though!  

I write in response: Yes, I see immediately what you are saying. This is a very good idea to fill that space (since we have way too much empty space within this machine)! It will also lend some additional interest in the demo mode and a good tutorial on Ferguson’s paradox.



The drawing in the third photo is 1:3 or 3X actual size. Buchanan writes: Today I finished the hub for Saturn, it does not look very fancy but every face is a reference face and it is in 2 sections so as to be able to hold another sleeve with two more gears. It took a lot of planning and cross checking and a little massaging to fit all in.


Buchanan writes: I have the Jupiter hub complete now. Another complicated part with every face a reference for some other part as well as three bearing fits and a screw assembly. You can see it carries a centre bearing for a concentric wheel.  I am now working on the embryo arms for Jupiter and Saturn. This mechanism is going to look really cool. Far more ‘spidery’, than the Tellurian.


These two photos show the brass blanks representing the arms for Jupiter and Saturn. Eventually these will become frames for the idler wheels to deliver the drive from the center shaft to those planetary gear boxes. The overhang of the Saturn assembly brings the diameter of the orrery to 13 3/8” (34 cm).

This video shows how freely the arms for the Jupiter and Saturn arms move. Reducing friction is always a constant issue in a machine that has so many moving parts.


The first wheels are scribed in the brass stock plate. Next these are fitted into the Jupiter arm.


Buchanan writes: This is where the 4 gears will be placed.  Everything will be squashed down a bit. There are bearings that are not pushed home properly yet. There are three more layers of gears to be fitted between these two arms (5 layers in total) and one gear layer above the upper arm and one gear layer below the lower arm. 

Next week I hope to complete this gear set, it also includes a clutch, and then I will start on Saturn, that will be ’fun’!  The first stage of Saturn will be the main lower arbour with the eccentric throw, then the angled section and then the upper gear set. I am very pleased with how the mechanicals are working so far, I was worried that I had made the centre shaft too thin (6 mm) but it is amply stiff enough.


The first photo shows a tool we have seen a few times before. This is the jig used to score lines for the wheel spoke design. The box on the upper left contains locating buttons for the spoke jig. They have a 6 mm spigot on one side and a section that fits the hole in the gear on the other and then a further thin spigot for the scribing ruler to locate on. He has a few stock sizes that he would normally use but this clock has so many special diameter holes on the gears that the box is steadily filling up. The fourth photo shows the most used tool to fabricate the flat stock for this project, the jeweler’s or fretting saw; seen here spoking out a wheel. This machine has been used to cut nearly every wheel, bracket, and frame in this project. It holds equal importance to flat stock fabrication as that of the lathe to round stock fabrication. Buchanan writes: I cut a small 54 tooth wheel this morning. It forms part of a collet for the Saturn Jupiter drive. I am now moving onto completing the outer gear set and its arbour. When complete it will mean that when I rotate the Saturn arm, the Jupiter arm will rotate at the correct ratio to Saturn’s speed.


Buchanan writes: Here are photos of the Saturn drive wheels.  I made 2 bearing caps, fitted two ball races, made an arbour and its retaining screw, made and finished 15 other screws, spoked two gears and mounted three gears.


Buchanan writes: The photo with the red pen shows the equivalent parts for the Hahn and Buchanan Orrerys. I want to only leave a thin arm supporting the outboard gear set.


These two photos show the completed Saturn gearbox mount first exploded and then completed. It contains three bearings and clutch assembly.  Notice the fine knurl located where the spring C-ring clutch is contained and will allow the operator to manually move the gearbox and thereby the entire Saturn assembly to achieve the correct tilt relative to any point in the planet’s orbit. Like many components within the complications of the behind-the-dial work, we are working on pretty small scales.

Buchanan writes: Here is the gear table for the orrery so far.  Row 2 to 6 are the drive between the Saturn and Jupiter arms. Row 7 to 15 is each a set of two gears for Saturn, Rows 17 to 38 are the individual gears for Saturn. Pixilated to protect proprietary data.

The two illustrations above show Saturn at its outermost from the Sun the Aphelion; the opposite side would be the closest, the Perihelion. These help answer the question of how Saturn’s tilt is positioned as it orbits the sun. It turns out that it holds its tilt relative to the sun exactly as does the Earth as it orbits the sun. Although the tilts are similar, 23.5 and 26.7 for the Earth and Saturn respectively, they are not aligned to each other. The gearbox clutch allows us to make that adjustment in any case. After some research on the web we see the outermost point of eccentricity, aphelion, Saturn is directly tilted toward the sun.  

Buchanan writes: A question: where do you want Dec/Jan to be on the orrery dial? In other words where do we want the earth to be on the New Years day, or at 0 degrees on the orrery dial? If we make 0 degrees on the orrery dial at the front of the clock, the point of greatest eccentricity for Saturn will be at the back of the clock and Saturn will be tilted forward, so that we can see the face of the Saturn dial ring best from the front of the clock.

I reply: Yes this is what I think is best since Saturn will be tilted forward to the viewer at all times throughout its orbit and the zero point is naturally at the front.


Unfortunately, because of the tilt needed for this complication, the maximum distance from the center point of the gearbox mount to the edge of the Saturn assembly occurs on the opposite side, when the tilt is directly facing the viewer. As explained above, the maximum eccentricity in the planet's orbit also occurs when the assembly is tilted forward and at the rear of the orbit when observed from the front, this is where Saturn passes the pendulum beat plate mount; and it will not clear it.

Deryck writes: I have Saturn physical dimensions complete. We are going to need a good horological shoe horn to fit everything into this space. At the moment it looks like it will be just possible. I have had to place the moon wires at an angle to keep within our sweep frame, as well as leaving space for the dial. This also helps when Jupiter passes on the inside. Space is so tight that I have to rely on the eccentric orbits to clear Jupiter past Saturn.

This is a reasonable compromise. In reality the elliptical orbits of Jupiter and Saturn precess in relation to each other; that is they rotate over time, so relying on the two to keep a constant relationship between each other to avoid collision is not really correct. However, those orbital rotations occur over millions of years so we won't be around to blame when our orrery's elliptical orbits no longer match reality!


The first photo shows how small the entire gearbox is, and this shows the box doubled by showing the tilt both left and right. Next the diagram placed within the machine, showing the tight clearances.


The eccentric bracket for Saturn’s gearbox is begun. It is the lower frame of a triple frame design. The mount assembly is attached.


A small bevel wheel is cut to allow the proper meshing with its mating bevel wheel that will be angled to 26.7. Next photo shows a view of a staking tool.



The staking tool is seen in detail attaching an arbor to the small bevel wheel, first photo. The next photo shows a thick brass blank in the mill to become the middle gearbox plate. Next a 26.7 angle is milled into that plate. The last illustration shows a drawing of a pair of bearings that will act as a main lateral support for the six cannon pinions controlling the five moons and the rotation of Saturn.



These four photos show how Buchanan neatly encapsulates a pair of bearings. First photo shows two bearings and their mating container cups next to the upper gearbox plate. Next one sees the upper plate has a threaded hole. The third photo shows the bearing pair encapsulated into a threaded ‘can’ made up of the two cups which then screws into the upper frame plate, fourth photo. There are many easier ways this could be done, such as a friction press fit, but Buchanan chooses the best way.


The rough Saturn gear box mount and plates are complete and the plates separated by temporary pilllars.


Notice in this photo the small gear sandwiched inside the small grooved area in the lower frame, this creates Jupiter’s eccentric orbit.

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