From the Loftsmith Workshop

Hand-crank Sun-Earth-Moon orrery, one crank turn per day

Turn the little crank and watch a blue Earth and tiny white Moon circle a yellow Sun, with the months printed around the big ring so you can see where in the year you are. One turn is one day. You can change the gear size and how big Earth and Moon are.

10 parts · 84 g · 175 × 137 × 53 mm

by Loftsmith Workshop

Gold gear arm with a yellow Sun, blue Earth and white Moon turning on a dark ring marked with the months
Loading the 3D view
Loading the 3D view
No adjustable sizes

Ask for the sizes you want to tweak, e.g. “make the width adjustable”.

Change it in the Studio

Parts

  • base · PLA · Flat, as modelled (toothed disc down, post up)

    Fixed 136-tooth Sun gear with the post and the engraved month ring; 137 mm across at default. About 45 g, 66 min. Suggested colour: navy.

  • arm · PLA · Flat side down, pins and hub up

    Carries the whole train round the Sun. About 13 g, 24 min. Suggested colour: brass/gold.

  • moon-wheel · PLA · 65-tooth gear down

    Turns once per synodic month; carries the Earth and Moon stalks. About 9 g, 18 min.

  • idler · PLA · 50-tooth gear down

    50/11 compound gear. About 6 g, 14 min.

  • crank · PLA · 10-tooth gear down

    Gear, hub, 45-degree swept lever and handle peg. About 2 g, 10 min.

  • moon-pinion · PLA · Pinion down

    11-tooth pinion with a D-shaft that goes up through the arm into the Moon wheel. About 1 g, 8 min.

  • sun · PLA · Flat side down

    Pressed onto the post; holds the arm on. About 6 g, 14 min. Suggested colour: yellow/orange.

  • earth · PLA · Flat side down

    Pressed onto the centre stalk of the Moon wheel. About 1 g, 7 min. Suggested colour: blue.

  • moon · PLA · Flat side down

    Pressed onto the Moon stalk. Under 1 g, 5 min. Suggested colour: light grey.

  • crank-cap · PLA · Flat side down

    Pressed onto the crank pin; keeps the crank on. Under 1 g, 5 min.

Print settings

Layer height
0.2 mm (0.16 mm gives smoother teeth on the gears if you prefer)
Walls
2 walls
Infill
15%
Supports
None
Notes
PLA for stiff, accurate gears on an indoor desk. At 2 walls/15% the whole set is about 87 g and 2 h 55 min on a Bambu A1 (engine estimate; slicer decides). At 3 walls/15% it is about 115 g and 3 h 48 min. Every part fits a 180 mm bed at the default module (the base is 137 mm). Print a few parts in a

Hardware

  • Superglue (optional) · Only if a press fit (Sun, crank cap, Moon wheel, Earth, Moon) comes out loose on your printer. No screws or other hardware.

Assembly

  1. Push the moon-pinion's D-shaft up through the bearing hole at the outer end of the arm from underneath, so the 11-tooth pinion sits below the arm.
  2. Slide the idler (50-tooth gear down) onto the arm's middle pin, then slide the crank (gear down) onto the pin near the hub so its 10 teeth mesh with the 50.
  3. Press the crank-cap onto the top of the crank pin until it stops, leaving the crank free to turn.
  4. Press the moon-wheel down onto the D-shaft so its 65 teeth mesh with the idler's small gear; its rim now holds the idler down.
  5. Press the earth onto the centre stalk and the moon onto the off-centre stalk.
  6. With the arm still off the base, turn the crank until the Moon sits at today's phase: full Moon on the far side of the Earth from the Sun end of the arm, new Moon between. The pinion is not meshed yet, so only the Moon wheel turns.
  7. Lower the arm over the base's post so the pinion meshes, with the arm window over the current month.
  8. Press the sun onto the post; it keeps the arm on.
  9. From then on, one anticlockwise crank turn (seen from above) is one day: the Moon goes round the Earth in about 29.5 turns and the arm goes round the Sun in about 365.

Good to know

  • This is a 10-part kit with press fits, not a one-piece print-in-place model. The press fits rely on printed holes coming out 0.1 to 0.2 mm small; a drop of glue fixes a loose one.
  • The arm and Moon wheel sweep a circle about 213 mm across at the default module (2 x 106.6 mm). It grows with the module slider: about 192 mm at 0.9 and 277 mm at 1.3. Keep that circle clear. The gearing multiplies your hand by about 365, and about 0.3 N on the handle of a blocked arm loads the Moon
  • Gear fit was checked only in the CAD engine (no tooth overlap, contact ratio at least 1.2). Teeth at module 1 need a well-tuned printer; if the train binds, reprint with a larger flank gap, or raise the gear module slider.
  • Ratios: 29.545 days per synodic month (about 0.4 h longer than the real 29.531) and 365.29 days per year (about 1.1 h longer than 365.24).
  • The Earth turns with the Moon wheel (once a month), not once a day, and has no axial tilt, so it does not show seasons or day and night.
  • The arm slides on the base's top face (PLA on PLA), and the Sun gear base is not fixed to the desk. Turn the crank gently and hold the base if it slides.
  • Not a toy for small children: it has small press-fit parts (the 6 mm Moon).
I printed this Remix

Comments