A model of the oldest known geared computer, found in a shipwreck off the Greek island of Antikythera and built around 100 BC. Turn the crank on the side: six turns are a year. On the front the Sun and the Moon go round the zodiac and the Egyptian calendar, and a ball on the Moon pointer turns half dark and half light with the phases. On the back two pointers follow spirals: five turns for the 235 months of the Metonic cycle and four for the 223 months of the Saros eclipse cycle, with a small dial for the four-year cycle of the Games. The gear trains use the tooth counts worked out from X-ray scans of the fragments, including the 127-tooth wheel for the Moon and the 223-tooth wheel for the Saros.
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18 × 21 cm. On the inside it carries the studs the wheels of the Moon train turn on, four pillars to the middle plate and the bearing block of the crank.
An open frame between the 223-tooth wheel and the 188-tooth wheel. It carries the arbor that takes the turning to the back dials and the stud of the Saros train.
Carries the back dials. On the inside: the fixed stud the 223-tooth wheel turns on (with a socket for the end of the Sun's arbor), the idler's stud, a bearing for the Saros arbor and four hollow pillars the M3 × 40 screws go through.
The twelve signs, every degree marked. Three 1.75 mm filament pins hold it on the front plate.
The Egyptian year: twelve months of 30 days and five extra days. It turns, so you can set it to the year, like the original.
Four clips glued to the front plate hold the calendar ring's thin outer edge.
b3, 32 teeth, with the tube that goes through the front plate round the Sun's arbor. It turns 13.37 times a year: once for every sidereal month.
Keeps the Moon pointer clear of the dial.
Points at the Moon's place in the zodiac. Two lugs carry the axle of the phase ball.
16-tooth bevel gear on the inner end of the phase axle. It rolls on the Sun's bevel gear, so the ball turns once for every turn the Moon gains on the Sun: a synodic month, from new moon to new moon.
A 4 mm hex axle from the pinion through the two lugs to the ball.
Faces you at new moon.
Faces you at full moon; at the quarters you see half of each.
16 teeth on the Sun's arbor, just in front of the Moon pointer.
Points at the Sun's place in the zodiac and at the day of the Egyptian calendar.
A 7 mm hex arbor through the Moon tube. It turns once a year and carries b1, b2, the Sun bevel gear and the Sun pointer; its round tail turns in the socket of the back plate's stud.
On the Sun's arbor. It drives both the Moon train (c1) and the Metonic train (l1).
96 teeth and the four spokes of the original's big wheel. The crank's pinion turns it once a year.
32 teeth that drive the Moon tube and, 15 mm behind them, the 32 teeth d2 turns.
38 and 48 teeth on one stud.
24 teeth and the 127-tooth wheel: 127 is half of 254, the number of sidereal months in 19 years.
38 and 53 teeth: the start of the Metonic train.
96 teeth, and 24 teeth that pass the turning on to the q arbor (a pair the original does not have: here the 223-tooth wheel fills the case, so m3 needs an arbor of its own at the edge).
The bevel gear the crank turns, with the 16-tooth pinion a2 that drives b1.
16 teeth on the crank shaft.
Between the bevel gear and the bearing block.
An 8 mm hex shaft out through the side.
Six turns are a year; 114 turns run the Metonic dial once round.
24 teeth and m3 (27) on a hex arbor that runs past the 223-tooth wheel to the back plate.
The Saros wheel: 223 teeth, one for each month of the eclipse cycle, the biggest wheel of the original. It turns on the back plate's stud; its tube carries e4 behind the middle plate.
On the hex of the e3 tube; it drives f1.
53 and 30 teeth on the middle plate's stud.
On the back of the q arbor. It drives the Metonic arbor's 53 teeth.
g1, 54 teeth, with the hex arbor out to the Saros pointer: 4 turns in 18 years and 11 days.
n1 (53) and n3 (38) with the hex arbor out to the Metonic pointer: 5 turns in 19 years.
44 teeth on the back plate's stud, between n3 and o1.
o1, 40 teeth, with the arbor out to the Games pointer: once round in four years.
The spiral of 235 months in five turns: after 19 years the Moon's phases fall on the same days of the year again.
The spiral of 223 months in four turns: after one Saros, eclipses come back in the same order.
The four years between the Olympic Games, with the games of each year, as on the original.
A straight arm on the Metonic arbor; its rider slides along it.
The same for the Saros dial.
Points at the year of the Games.
Slides along the Metonic pointer; its pin runs in the spiral groove and points at the month. At the end of the spiral, lift it back to the start, as on the original.
The same for the Saros spiral.
For a 0.4 mm nozzle. Filament amounts are estimates for these settings.
Nothing needs supports. Print the gears at 0.12 mm: the 223 and 188-tooth wheels have fine teeth (module 0.75). Clean any elephant's foot off the gears and check that every wheel turns freely on its stud.
Lay the front plate face down. Put the Moon tube through the middle hole from the inside, then the wheels on their studs: e1 and e2, c1 and c2, l1 and l2, d1 and d2, m1 and m4 and the crank wheel. Hold each with an M3 × 8 screw and washer in the counterbore.
Glue b2 and b1 on the Sun's arbor (b1 at the back end) and push the arbor through the Moon tube, b2 in mesh with c1 and l1, b1 with the crank wheel's pinion.
Push the crank shaft through the bearing block from outside, with the spacer and the crank bevel gear on its inner end in mesh with the crank wheel. Press the crank onto the outer end.
Put the q arbor through the middle plate and the 223-tooth wheel on its place over the middle hole, then lay the plate on the front pillars: q1 in mesh with m4, m3 with e3. From the back put e4 on the e3 tube, f1 and f2 on the stud, m2 on the q arbor, and the Saros, Metonic and Games arbors with the idler on the back plate.
Lower the back plate on: its stud goes into the e3 tube and the Sun's arbor into its socket. Screw it all together with the four M3 × 40 screws from the back. Turn the crank: every pointer should move.
Pin the zodiac ring on the front, lay the calendar ring round it and glue the four clips over its edge. Put the spacer and the Moon pointer on the Moon tube, push the phase axle through the lugs with the pinion on its inner end and glue the two halves of the ball on its outer end. Glue the Sun bevel gear and the Sun pointer on the Sun's arbor. On the back pin the three dials on, push the pointers onto the arbors and slide the riders on, their pins in the grooves.
Small parts and screws: keep them away from young children.
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