Lighted 3D Moon Phase Clock

In this Instructable, I will describe the design and build of a clock that shows the current phase of the moon in a lit 3D printed moon model. This project started this summer when I began to think about a project for my new 3D printer. I had printed accessories for the printer and chose a moon lamp (https://www.instructables.com/Moon-Lamp-With-Remote/) . I thought it would be nice if it could show the moon phases and saw in the comments someone else had the same thought. So I began thinking about a design and this is what I came up with. It was also an opportunity for myself to learn the basics of Fusion 360.

Some General Background

A simplified description of the lunar phase cycle will be used that is based on the average cycle of lunar phases, the synodic month. The synodic month averages 29.530588 days, but can actually vary between about 29.18 to about 29.93 days in any individual cycle, due to the elliptical orbits of the moon and the earth. This results in variations of up to seven hours about the average in any given year https://en.wikipedia.org/wiki/Lunar_month#Synodic_month. The side of the moon facing the earth is gravitationally locked (tidal locking) so we see essentially one hemisphere of the moon from earth. In actuality, over time we see about 59% of the moon due to lunar libration. Libration from our perspective on earth is the slight top/bottom rotation (like nodding yes), left/right rotation (like nodding no) and tilting back and forth (like a metronome) of the moon resulting in an apparent wobble. This is due mostly to the eccentricity of the moons orbit and a slight tilt (6.7 degrees) of the moons rotation axis to its orbital plane, along with the earths tilt. See: https://en.wikipedia.org/wiki/Libration , https://moon.nasa.gov/moon-in-motion/moon-phases/#otp_our_wobbly_moon.

Lunar Libration and the variability of cycles will not be considered for this project.

An interesting additional note is the saros or eclipse cycle. The saros cycle is 223 synodic cycles, approximately 6585.3211 days, or 18 years, 11 days, 8 hours where the Sun, Earth and Moon return to approximately the same relative geometry. Note that this is not a perfect multiple of a year or the same time of day, so basically the positional relationships between the Earth, Sun, and Moon effectively do not ever repeat perfectly, but come pretty close on slightly longer than an 18 year cycle. See: https://en.wikipedia.org/wiki/Saros_(astronomy), https://eclipse.gsfc.nasa.gov/SEsaros/SEsaros.html

Supplies

Supplies:

High torque quartz clock movement with long shaft (28-29, or 31 mm) and accessories, metal I-shaft minute hand with step second hand drive.

Examples:

High Torque Quartz Clock Movement, 11/16" Maximum Dial Thickness - 101150 (28.5 mm, 1-1/8")

High Torque Clock Replacement Movement, Clock Movement Metal Clock Needle Kit,31MM Long  (Cut off the plastic hanger)

High Torque Quartz Clock Movement Replacement Parts …(31 mm (1-1/ 5 inches))

High Torque I Shaft Hands Quartz DIY Wall Clock Movement Mechanism...4/5 in Max Dial Thickness, 1-1/5 in Total Length

Clock Movement Mechanism with 5 Different Pairs of Hands, High Torque Long Shaft Clock Movement Quartz

clock second hand (to use or obtain mounting pin from) or short piece 1.5 mm tube, minute and hour hands (if not printing your own)

Stainless steel rod, 1 mm diameter

Example:1mm x 200mm 304 Stainless Steel Round Rod, Metal Solid Shaft Rods Lathe Bar Stock ... 10pcs

PLA filament (white, black, plus you're choice)

Screws for mounting clock assembly (2x) #8 x 1/2" sheet metal

M1.4 -2.5x6, 2.0 x3.0, x3.4, x3.8, x4.0 mm machine screws, eyeglass/watch screws

Example: Eyeglass Repair Kit

A few inches warm white ribbon LED (or small low voltage & wattage LED bulb with base) and matching wall transformer with appropriate DC voltage

Example: Olafus 16.4ft LED Strip Lights Warm White Dimmable, LED Rope Light Kit

Hook up wire (red and black) and connector matching wall transformer -

Example:FSJEE 2Pin 8MM LED Connector Kit....

5 minute epoxy

Super glue (CA)

Clear water based glue (for clock face)

Dry lube (Teflon, MoS2, graphite); I used - B'laster 16-TDL Advanced Dry Lube with Teflon 

Tools:

3D printer ( I used a Creality Ender 3 Pro)

Hobby knife ("X-Acto")

Sandpaper (fine, 320 or 400 mesh)

jewelry screw driver set

Jewelry needle file set

Sharp tweezers

Rotary ("Dremel") tool with abrasive cutting wheel and grinding wheel

Pin vise w/chuck

Set small metric drills (0.7, 1.0, 1.3, 2.7 mm)

Small spring clamp

Hot glue gun

Diagonal wire cutters, needle nose pliers

Solder iron / electrical solder (lead free)

Drill/Drill bits

Digital Calipers

AutoDesk Fusion 360 (optional for any changes / new pieces)

Step 1: Design Concept

The design started with a single main desired feature; Make a 3D moon lamp that showed the current moon phase. I also wanted essentially all fabricated parts to be 3D printed. The concept builds around adapting one of the popular 3D printed moon lamps to construct this. An obvious solution is to put a rotatable hemisphere inside the moon model to shadow the lamp and create the appearance of the moon phases. The general problems to solve and design for are thus:

• put the hemisphere in the moon lamp shell
• rotate the hemisphere with the lunar synodic period of 29.530588 days
• light it internally to get the desired shadow effect

For the first point, the simplest solution is to split the moon model in half to insert it. Otherwise, possibly a segmented hemisphere that could be passed through a hole and internally assembled or a flexible hemisphere that would recover its shape after being inserted through a hole might be designed. In this case, I chose the simplest solution. Also, since the side of the moon facing the earth is gravitationally locked, I chose to only use this side. Using only the earth facing side also helps provide the visual cycling of a dark new moon → 1st quarter → full moon → 3rd quarter → back to new moon over the lunar synodic cycle of 29.530588 days. In the design, it was also considered that it would be an easy substitution to use the “dark” side of the moon, but gluing the two halves together would be required.

To rotate the hemisphere, an "analog" clock drive or or a digital clock micro-controller driving a motor (stepper or encoded) could be used. I wanted a simple solution for continuous operation so I looked at analog clock drives. With some quick searching, inexpensive battery powered quartz clock movements with “high torque” and long shafts are readily available. These are intended for large diameter wall clocks with relatively long (and relatively heavy) hands. The long shaft (with modification) would be suitable for fitting a gear to the hour hand shaft. The question was whether these clocks could provide enough torque to rotate the hemisphere shell. My gut feeling was with the high gear ratio required (~1:59) and the high mechanical advantage, the chances were good that it could work, provided the mechanism operated smoothly. I also decided to include an analog clock face in the design. Not only is this a desirable feature overall, it also provides an immediate and long term indication if the clock movement is stalling or skipping. As a backup, there was always the solution of a micro-controller clock or even a 1 rpm AC synchronous motor to run it.

Finally, being able to light the system with power, the geometry requires wiring and lamp supports to be coaxial to the axis of rotation but not rotate. A large enough hollow drive shaft for the rotation of the inner hemisphere will provide this access to the inside.

Now with the basic concept to begin the design around, a gear reduction box from the hour hand shaft to the moon internal hemisphere with a gear ratio of close to 1:59.061176 is needed. I had initially guessed there would be various websites/freeware or methods for optimizing the number of teeth on each in a gear train to obtain closest to a specific ratio. It turns out designing a multi-stage gear box for a specific irrational ratio is non-trivial. After a few different keyword searches, I came across a website hosted calculator, Gear Train Calculator, and is shown in the screenshot with the results for the gear ratio used here. I chose the min/max teeth and number of stages with the design in mind, trying different combinations. The final gear needed a larger number of teeth (large diameter) and the first gear needed an ~6mm shaft diameter and preferably a smaller diameter (fewer teeth). A theoretical description of the gear train calculator by the original author can be found in the Physics Forum , PhysicsForums - Gear Ratios to Gear Tooth Count. The gear combination chosen actually has a incredibly small deviation of < 1min in 25 years.

Step 2: Gear Box and Clock Design

The gear box was designed in Fusion 360 using its included sample add-in for designing spur gears and a parametric bevel gear model (thingiverse.com/thing:3336648). Additional gears with 1:1 ratios having 14 teeth and 20 teeth (bevel) were inserted before the final 2 gears (13:35) to correct rotation direction, adjust overall height of the gear box and make the 90 degree turn. The first 17 tooth gear is press fit on the hour shaft of the quartz clock module. The clock module was modified by trimming away part of the threaded mounting shaft using a rotary cutting tool to expose additional length of the hour shaft. The next 3 compound gears (59:16, 41:15, 37:14) rotate freely on a 1mm shaft. A 14 tooth gear then drives the bevel gears which outputs to the 13 tooth gear through 1mm axles. These gears have set screws and the axles have hand ground flats to prevent slippage. The final 35 tooth gear has a 21.5 mm shaft diameter for the large hollow shaft driving the inner hemisphere. The gear box is about 90 mm long from the quartz clock shaft to the hemisphere drive gear. This will be suitable for a 5 inch (125 mm) clock face. A 4 inch (100mm) moon model was chosen. The clock with moon hemisphere, lamp, and clock base were then designed, shown in a few views. The moon is represented here with a simple hemisphere since the actual moon model slows Fusion 360 on my computer too much. A small modification to the gear box shown here was made for using a slightly shorter shaft quartz clock (28_29 mm version) and is also included.

Step 3: Prepare the Moon Model

 The moon model utilized was derived from the excellent NASA CGI Moon Kit 2019 Moon Lamp (https://www.thingiverse.com/thing:4102658) 4 inch version. The developer of this moon model has also authored a series of moon Instructables with the most related one, https://www.instructables.com/Simplified-NASA-CGI-Moon-Lamp/. The moon model was split and a cylindrical base added using Fusion 360’s mesh and design tools.  This was quite a slow process on my laptop (hours crunching). The moon mesh model can be cut using with the combine tool using a large enough mesh box as the as the cutting tool (cut half the moon away). I had problems with the plane slice tool. The inner shell and outer shell were not bridged together with mesh and repair didn't produce the desired result. It would just fill the whole cut surface even inside the inner shell. A mesh cylinder is then used to cut the hole, then a pipe shape mesh is combined. Sometimes the mesh needed repaired with close holes. Over the course of the project, I did this entire process several times due to changing the moon model used, design, etc... Due to file size limitations the prepared moon model .stl file can be downloaded here, 3D moon phase lamp clock 4inches. Print the moon model at 10% uniform scaling for the correct size.

Step 4: Print the Parts

The gears and retaining ring were printed with 0.12 layer height and 50% infill. It was found the gears except the 13/35 teeth pair needed to be printed at a scale of 99% in X/Y from the design for the gear box to run freely. Note that meshing gears should always be scaled identically. The 13/35 teeth pair was kept scaled at 100%. In early tests, the spur gears ran tighter in a 180 degree cycle suggesting an aspect ratio problem. I then noted in Cura the X and Y dimensions for the spur gears were not identical (not sure why), while for the bevel gear they were identical. Adjusting the Y scaling separately to obtain a dimension in Cura that was very close to the X value for each gear seemed to fix this issue. The important point here is the gear printing needs to calibrated one way or another so that the gears are nearly perfectly round. Two different versions of the gearbox are included for 28_29mm and 31mm shaft length quartz clocks, for which slightly different heights of the 59:16 gear are needed. The gearbox and associated miscellaneous parts, bottom case, top case, and top back were printed 0.2 mm layer height and 33% infill. T The top case was printed with tree supports. The inner hemisphere was printed 100% infill and 1.2 mm shell setting. The moon model was printed with supports (tree, 60 degrees shelf angle) with 0.16 layer height, 1.2 mm shell, 100% infill, and 10% uniform scaling.

Step 5: Prepare the Parts for Assembly

Clean up all the printed parts. Closely inspect all the gears and trim or shave away any excess PLA (hobby knife). Pay particular attention to the teeth. If there any significant defects on a part reprint it.

Drill out the shaft/axle holes and set screw holes on the gears and gear box by hand with a pin vise and 1.0 mm drill. Check that the gears spin freely on 1mm stainless shaft.

Drill through the shaft/axle holes on the gear box with the 1mm drill with the pin vise.

Clean up the hole for the quartz clock movement so it fits with a round file, knife or drill (I used a 5/16 drill by hand).

Drill with pin vise the set screw holes further with a 1.2/1.3 mm drill (test which works better) and fit a suitable length M1.4 screw. This is slightly longer than the required depth to tighten on axle. I just let them self tap. Note: any suitable miniature screws could be used as long as the length will not interfere with other surfaces in the final assembly. Also photo shows M1 screws in the 14 tooth gear which I later changed to M1.4.

Test fit the inner hemisphere, the axle cylinder, spacer ring, and final gear. On the top and bottom surfaces of the hollow cylinder on the inner hemisphere, carefully remove any bumps/roughness with a flat file and/or fine sandpaper on a flat surface. Gently sand the bottom surface on a flat with concentric motion. Repeat the same with the upper sliding surface of the 35 tooth final gear. I had to reprint the axle cylinder with scaling at 98.5% in X/Y for the correct fit. With a file and/or sandpaper remove any seam bumps on the axle cylinder and sand lightly, if needed, to fit. The axle cylinder should fit snug in the inner hemisphere but should be able to be turned with some resistance, as this is the method to set the current moon phase when setting the clock. The final gear should slide on easily but with essentially no side to side play.

Trim the metal screw on the shaft of the quartz clock module. I did this with a rotary tool (Dremel) with an abrasive saw blade; Wear safety glasses and avoid being in the same plane of the blade (especially your face) in case the blade fails. You can use a sharpie marker or tape to mark the line. Very carefully grind through the metal, trying not to contact the underlying plastic hour shaft. I cut this on twice; I left it too long first cut. Leave at least 5 mm of the thread, but it only needs trimmed enough to fit the gear far enough on. In retrospect, I cut away too much on the second cut and should have left about 10 mm, but it was still OK.

Size the 17 tooth gear to fit the clock hour shaft for a press fit (quite snug) with fine sand paper on a round mandrel, if needed. Do not actually press it on fully yet, although it shouldn't be so tight it can't be pulled back off. If it is too large the part will need scaled slightly or modified with smaller shaft hole and reprinted. In principle, scaling shouldn't be done as it changes the module of the gear but the change should be insignificant assuming the clock hour shaft is ~5.7 mm. Note the hour shaft is stepped with the diameter for the hour hand slightly smaller.

Step 6: Assemble the Case

First, test fit the moon hemisphere, the bottom case, top case, and retaining ring. Trim around the base of the moon with knife or file, as needed, to get a good fit. A minimal gap is desired between the back face of the moon and top case. The retaining ring should fit tightly on the moon model. Lightly file and sand the cylinder to and bottom surfaces on the moon to remove any roughness and seam bumps; Don't remove much material and be careful to keep them flat .

These parts can be then be final assembled at this point. I used 5 minute epoxy and a clamp for the top and bottom cases. The moon can be held in place with painters or masking tape. After the 5 minute epoxy set, I applied liquid CA glue from inside the bottom case and then fitted the retaining ring. Since the top and bottom cylinder surfaces on the moon model are sliding surfaces for the inner hemisphere assembly, they must be kept clean of glue.

The back face of the moon was glued to the top case with superglue just at the very top. If desired, a 3D pen might be used to fill any gaps and glue to the top case.

Drill out the small holes in the top back for the mounting screws. Drill the small holes in the back of the top case with a drill size suitable for self tapping the screws. I used some 6-32 screws I had.

Make paper templates for locating and gluing the clock face and numbers on the case and glue in place. I did not use CA for the clock face, but rather clear water based glue to allow time for positioning and the CA seems to discolor the PLA even away from the glue joint (fumes?).

Step 7: Build the Gear Box

Cut the 1mm rod into 5 lengths for the shafts/axles with diagonal cutters. Leave them a little long as they can be trimmed later. Clean up ends with rotary tool and grinding wheel.

The gear box here is for a 28_29 mm shaft clock movement. Start with the 59 tooth gear and assemble the gear box. As gears are added test for smooth operation. Note that the second 1mm shaft stops inside the box in a divider as the 59 tooth gear won't allow it to go all the way through.

Grind small flats on the axles for the set screws. Try to keep the flats on the same side, so the set screws align. Once the 1st bevel gear is fit, gently test run the gear box turning either the bevel gear by hand or the 37 tooth gear using a fingernail. If resistance is just slight, I found it can loosen with spinning the gears. It needs be able to spin pretty freely, although running the gear box backward occasional binding may occur.

If it is too tight, all the gears, 17 teeth through the 14 teeth will need printed with slightly smaller scaling. Note these gears need to be printed all with the same scaling. The bevel gears can be scaled separately, if needed (were originally printed at 99%).

The red circle indicates a glue on part for eliminating rotation freedom of the clock body (clock rotation stop) which was later removed. It interfered with the clock positioning and clamping in the case and is not really needed. The clamp itself serves this function. The part is shown in the drawings/figures and the .stl file is still included, however, to avoid confusion.

Last, trim and glue in the support on the open side of the gear box. This is to limit squeezing of the box by the mounting clamp. Be careful not to get glue on gears.

Step 8: Install Rotating Inner Hemisphere

Test fit the inner hemisphere, axle cylinder, spacer washer (optional), and 35 tooth final gear. The spacer washer can be used to adjust the height of the inner hemisphere. It was not used in this build, but if used flat sand the surfaces.

Apply dry lube to all the sliding surfaces. With spray dry lube (in solvent), I wet a sponge swab to apply rather than directly spray parts. This should make the dark surfaces have a visible cloudy white coating. Other dry lubes like graphite or MoS2 may also work fine.

Assemble and lightly snug the set screws and test for ease of motion. The inner hemisphere should be able to rotate very freely with minimum tilt, in particular, when vertical. This is perhaps the most difficult step to fully describe, since you need to keep troubleshooting, adjusting gear position, possibly additional sanding, until the rotation is quite free with no noticeably more stiff positions.

Tighten the set screws and do a final test. The sensitivity of this step is why I don't recommend using the set screws for setting the current moon phase. Note the set screws used must be short enough they can't interfere with rotation of assembly.

Step 9: Build the Internal Lamp

The possibilities for fitting an LED lamp are endless. I choose to build a simple lamp assembly with warm white LED strip lamps.

Solder wire to the LED strip at 90 degrees and coat with hot glue to fix joints and prevent shorts breakage.

Slip through upper tube and slide strip lamp at solder joints into slot and wrap around tube (remove adhesive backing). Cut at cut line and hot glue at cut to hold on tube.

Prepare splices to power supply connector with heat shrink tubing (2 smaller diameter for each lead and 1 larger to shrink on entire joint. Solder splice and shrink the tubing one at a time with heat gun, solder iron side, or lighter.

Test the lamp.

Attach the lamp post to the gear box with hot glue and check center position in clock. The slot should be oriented to the close bottom side of the gear box. Redo to adjust position for center, as needed.

Step 10: Final Assembly

Test fit the clock gearbox. Note how tightly the 13/35 teeth gears mesh by noting whether the clock sits flat on the base. You can also slide the clock gearbox up and down to judge how tightly the gears are meshing. I decided to use a thin shim (washer shape in photo). This was an old brim from a print.

Pass the connector for the lamp through the opening and push the wires into the slot in the lamp post.

Drill or file the holes in the clamp cross member to loosely fit the mounting screws. I used #8 x 1/2" sheet metal screws. Fasten down the clock assembly while centering the clock shaft in the hole.

Adjust the set time knob on the clock, so the minute hands flats are vertical. Add the clock hands all at the 12:00 position. The hour hand is friction fit and the hole may need sized with sandpaper/round file to fit. The minute is for an I-shaft with retaining nut. It may also need enlarged with needle files. The second hand can be used 2 ways. First, as done here, the center mounting button was removed from a second hand supplied with a clock module. The printed second hand was drilled and shaped to fit and then glued in place with CA. Second option is the hole can be enlarged for a ~1.5 mm diameter section of metal tube that fits the second hand shaft and glued in with CA. The tube may be crimped slightly to friction fit the second hand shaft.

Install the AA battery, set the time, and adjust the moon phase. To get the current moon phase one place to get it is https://www.timeanddate.com/astronomy/usa. To adjust the moon phase tightly hold the 35 tooth gear and rotate the inner hemisphere to the correct angle. It is easiest to set best at full, new, or quarter moon times.

Install the top case back. Plug in the light. If the clock is running and keeping time (I did not have any problems with the prototype and this version) the moon will slowly move continuously.

Step 11: Conclusion

A clock has been successfully constructed that shows the current moon phase on a internally LED lit 3D moon model using a quartz clock module to drive the moon phase motion. The original prototype has been running for over 2 months. This version was built to document the build for this Instructable and verify all the various modifications done while constructing the original prototype. This build was using a different clock module than the prototype which introduced a few minor changes due to shaft length and dimensions, thus 2 different gear box frames are included. This build uses the first quartz clock module listed in the supplies. The original prototype test system uses the second one.

Although the systems works well, functional changes I would explore include: (1) using larger diameter axles in the gear box for more stiffness (the last 2 shafts with set screws) with perhaps bearings or sleeves; (2) using a thin wall bearing for rotating the inner hemisphere as this was a bit touchy to make work smoothly; (3) test printing the gears with a smaller nozzle.

If you build it, Enjoy All You're Hard Work!

Thank you for reading and I hope you enjoyed this Instructable. Please share any builds and modifications.