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Orrery, Jupiter armature drive wheel set  - November 2018

This photo shows the beginnings of the armature for Jupiter. At this point it is a simple rectangular brass slab with the Jupiter gearbox mounted to the end.



Due to space constraints Buchanan must check carefully the positions of Jupiter and Saturn as they would pass each other in their closest and farthest positions relative to each other due to their planetary tilts.


The first photo shows the computer design image used for the engraving of the Jupiter’s orbit dial. The next photo shows the beginning of the engraving process. Notice the brass blank has teeth around the perimeter; it is a recycled wheel from a prior project.


The toothed rim is cut from the rough-engraved blank and in the second photo the surface has been sanded smooth, revealing the dial engraving.



These photos show the orbit and degree dials finished with black dial wax to fill the engraving and the surfaces silvered. Then the dials are ‘dressed’ with their internal and external bezels, the latter having a knurled edge. The units denoted on the orbital dial are AU and Mkm. The AU is the mean distance of the Earth to the Sun, the astronomical unit. Mkm is shorthand for millions of kilometers from the Sun. Both are measurements of the distance of Jupiter from the Sun in its elliptical. The semi-major axis is one-half the major axis which is the longest diameter of Jupiter's elliptical obit. The second dial is a a degree ring from marked from 0 through 360. This allows one to measure the moons orbits around Jupiter. Since each moon moves at a different speed one can measue their relative motions with this dial.

The parts count for the Jupiter gearbox assembly is 89 parts.

The Jupiter gearbox and its own little world of moons is finished.

Buchanan writes: Jupiter is finished. On to the Jupiter arm. I will first get a rough arm design, (I will reduce the Saturn arm design on the photo copier), then I can fit in the largest possible size gears and then we can go on to the final design once everything is on the arm. This arm has an extension out the back that carries the Saturn arm drive gears so will be rather different finally.

The Jupiter armature plate is mounted into the orrery to test for fit within the dial. From this angle the dial work of the tellurian and sun /moon complications on the right flow across the front, up and around to the rear of the machine.

Another view of the Jupiter armature plate.


The first illustration shows two options for the Jupiter armature; the lower one was chosen. The next illustration shows the design under the actual armature plate with the holes aligned.



Buchanan writes: I have the centre drive gear mounted on to the bearing sleeve 934 (1st photo) in machining the gear to fit the sleeve, 909 (2nd photo) is the sleeve assembly, there is another input wheel to be added that brings the drive from the centre gearbox. 248 (3rd photo) is both gears mounted on the arm.  604 (4th photo) is a test gear to check the tooth count and establish the depthing of the idler gear. These four gears will have 252 teeth each. Just another 1004 teeth on the clock.


The four large idler wheels, each having 252 teeth are now being cut from the brass sheet.


Buchanan writes: Here we are cutting the batch of four gears at one time as a stack of four (1st photo)(2nd photo) is the Jupiter arm mounted on the jig borer and centring on the brass mushroom spigot, so that I can machine the arm for the gear bearings. You can see the basic arm design scribed onto the brass plate so that I could place the brass mushroom centre over the design.



Buchanan writes: The bearings are fitted into the Jupiter arm (1st photo). I had to reduce the thickness of these two bearings due to space constraints (2nd and 3rd photos). I have also made the outer concentric arbour and am now machining the 1.6 mm thick gears down to 1mm thick (4th photo).


The first photo shows the scribing of the circle defining the wheel hub. Next photo and below are Buchanan's spoke scribing jig.


The second photo shows the trusty scroll saw responsible for the thousands a spokes cut as well as all of the rest of the flat stock in this machine, from the frames, to the pendulums to the strike lever work.


Buchanan writes: Here are a few more steps in making a gear. Once the blank is to thickness I mark out the rim and the hub diameter  on the jig borer. (1st photo). Then I mark out the spokes on the spoke jig by using the adjustable rule and flipping it over for each spoke the taper is totally symmetrical. (2nd and 3rd photos).Then I drill starting holes for the scroll saw and the spokes are cut out. The actual cutting time is 30 minutes for this gear (4th photo). Then the spokes are filed up and a semi finish applied, (5th and 6th photos).


The center hub is drilled and tapped, 1st photo, and the hub attachment is then secured. The small ball bearing just above will fit into the center recess area. There is an arbor that passes through the center to carry the next set of wheels.



The wheel set, and those wheels set into the blank armature plate, (photos 1 through 3). Photo four shows that armature installed into the orrery with Saturn opposite. Note the set of horizontally mounted wheels beneath the orrery visible through the front quadrant of the dial mount. These are part of the two-speed transmission for the orrery drive.



Buchanan writes: (1st photo), 754 is burnishing a spoke with a hard polished rod. The rod is just rubbed backward and forward along the length of the spoke and smooths the surface. A lot of English clock makers finished their spokes like this in the old days. (2nd photo), 207 is the surface plate and cork block that I use to finish flat surfaces. And 115, (3rd photo) is the gear under the block. Light pressure is needed or the part is pressed into the sand paper and the surface becomes domed.

I did a quick calculation and there are 25 inches of scroll sawing on each wheel, so, this batch of 4 wheels have 100 inches of polished edge! That is 100 inches of cutting 100 inches of rough filing 100 inches of fine filing and 100 inches of burnishing. There are also 96 square corners to make sure they are perfectly sharp and square with no saw or file marks. And I wonder why my fingers are stiff at the end of the day.

The Jupiter assembly before the armature plate is fretted into a curvilinear frame.




Buchanan writes: Today I semi-finished the Jupiter arm (made 2 more filing buttons), (1st and 2nd photos). Drilled and tapped the mounting screw hole for the pointer, (3rd photo) and made the bearing holder for the lower end of the input arbour (4th and 5th photo), then I spoked the input wheel and almost finished its collet (6th photo).

If all proceeds well tomorrow I hope to have Jupiter completed as far as I can at this point.

I am formulating a few ideas for the centre gearbox right now.  I have an embryo idea for the centre frames that could look very nice. It looks like I could stretch the diameter of the centre box quite a lot and make it very ‘transparent’.


The first photo illustrates the very thin wheelwork. The four large wheels are only 1.0 mm thick and are stretching the mechanical strength of such large, thin wheels to the limit; fortunately these are all very lightly loaded and so will keep their integrity. This design is necessary due to vertical dimensional constraints as a result of the numerous stacking of wheels that had to be balanced between the individual planetary gearboxes and the central orrery drive hub which has to feed all of the four inner planets as well as the outer planets of Jupiter and Saturn.

This photo is a close up of the prior photo and illustrates the intricate turning work Buchanan employs on what other makers would have left plain. In the circled area the collet has four stepped 'necks' while the arbor directly below has three. A single step could easily have been employed on each. The small input wheel to Jupiter gearbox is fully spoked with six arms, whereas other makers when making such small wheels do not bother to spoke them. A small knurled disk is tucked inconspicuously between the bottom orbital dial its drive wheel. That knurl is what is used to tighten the Jupiter gearbox onto the armature. Remember all of these parts are very small, less than a 3/4" or 2 cm, and located below the dial, a location that will largely be unobserved, yet the attention to detail and craftsmanship remains undeminished.


These photos show the orbital dial hand and decorative turning of the tiny pillar and screw holding that hand. The upper set for Jupiter, the lower belonging to Saturn’s orbital dial.

An additional 60 parts within the drive armature added to the 89 contained within the Jupiter gearbox.


These two photos show the completed underside of the Jupiter / Saturn assemblies; left with the planets at their furthest point, and right their closet point to each other. The large transfer wheels fulfill their function of filling in the empty space between the planetary gearboxes.

A rear, three-quarter view of the Jupiter / Saturn assembly. Buchanan's trademark feather-light wheel works are on full display.

An edge-on view of the Jupiter / Saturn assembly. The large transfer wheels from this angle seem to dwarf the planetary gearboxes, yet fill the space between those and the central hub.

This photo nicely shows how Buchanan has created both an airy yet substantial design; eliminating the mundane conventional rectangular armatures to the outer planetary gearboxes with elegant, inconspicuous and sinuous frames. The wheels fill in the spaces between and prevent the two outer planets from looking like two rotating islands within a largely empty space. In this angle the planetary gearboxes hold their own in visual bulk.

What can I say? The planetary pair above the revised, more colorful orrery dial is perfect.


In this video the orbits of the moons around Jupiter and Saturn and the orbits of Jupiter and Saturn around the Sun are demonstrated as they move past each other. Note the large transfer wheels that nicely fill in the space between the planetary gearboxes and the central drive hub of the orrery. This design is in stark contrast to most other orrery designs that use a strait armature with a set of identical idler wheels to transfer the drive from the hub to the planetary gearboxes, leaving the planetary gearboxes to look like islands in an empty space between the outer planets of Jupiter and Saturn and the central planets of Mercury, Venus, Earth and Mars.

The front elevation shows how the elements of the orrery are beginning to fill the last open space left on the clock.

This three quarter view reveals the immense complexity of the machine. The orrery seems to disappear amongst the forest of wheels. For a long time there was a concern that the right side of the clock with only the bell set was visually too sparse in comparison with the density of the left end of the clock, containing the remontoire. After the addition of the sun / moon dial set located just above the tellurian, all that changed with the addition of the the dual Janvier variable differential slant wheel sets located behind that dial work. 

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