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3D Printed Pendulum Clock

A 3D printed clock in PLA. It has an 8 day runtime with an accuracy of 1-2 minutes per week.

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I have always had a fascination with mechanical pendulum clocks so I designed one to be printed on my Prusa MK3. There are a few other 3D printed clock designs on the web, but most seem to have runtimes of 12 hours or less. I wanted to see if it was possible to extend the runtime to several days with the ultimate goal of 8 days per wind. This design evolved over a six month period to achieve that goal. A video is at https://youtu.be/imYTm0Vh5TA

Involute gear profiles were designed using Gearotic and imported into TurboCAD for final adjustments.  One of the first experiments was to determine a good gear tooth size.  They needed to be large enough to print accurately, but not so large to exceed the capabilities of my printer.  I printed an assortment of gear sizes ranging from 10 dot pitch down to 40 DP and selected 20 DP as my favorite.  A 20 DP gear with 60 teeth will be 3" in diameter.  Smaller pitches were possible, but some of the teeth were slightly distorted.  I printed the gears in gold colored filament to get them to look like brass.

The next step was to design the overall gear train.  Most pendulum clocks share the same basic structure with differences in the gear ratios.  The basic requirement is that the minute hand should rotate once per hour and the hour hand should rotate once per 12 hours.  These gears are central to the clock design with hands and a dial added to display the time.  I used a traditional Roman numeral dial for this clock.


A pendulum provides an accurate time base depending on the length.  The escapement advances one position per pendulum swing and provides a small push to keep the pendulum swinging.  This clock uses a deadbeat escapement designed in Gearotic.  A traditional clock design with 60:8 and 64:8 gear ratios would need a 39" pendulum rod which seemed too long for this design, so I added a 3rd gear to allow for a shorter pendulum.  Three sets of gears with 54:12 ratios drive a 30 tooth escapement and a 17" pendulum with 5467.5 beats per hour.  This gives a balanced look but loses the ability to add a second hand.


The final component of the gear train is the weights.  A falling weight provides power to the minute hand which in turn pushes the escapement.  An 8 day run time with 52" of drop means that the weight will drop 6.5" per day.  A pulley doubles the length to unwind 13" of cord per day.  A 1" winding drum will only rotate once every 6 hours.  Two gear sets divide this down to one rotation per hour of the minute hand.  The weight shell holds 4.5 pounds of lead shot to provide just enough power to keep the clock running.  Some of my initial experiments used a larger weight shell and a 3:1 divide ratio with only a 4 day run time.  I added steel bushings to several critical locations to reduce friction enough to use the 8 day gear set.


The clock frame consists of two major components.  The back frame integrates a metal keyhole hanger to hang the clock on the wall.  Standoffs push the clock body away from the wall for pendulum clearance.  The top of the frame has a robust support bar to prevent frame sag from the heavy weight shell.  This design could easily handle double the weight with no visible sagging.  The support bar also includes a convenient location to store the winding key.


The front frame integrates the dial and numbers into a single 3D print.  The first few layers are printed tan colored with pauses for the ivory colored dial and black numbers.  The same multi-layer technique is used to add gold highlights to the clock hands.  The front and back frame sections just barely fit diagonally on the MK3 print bed.  The pendulum is a two piece clamshell with a few pennies added for weights.  It pivots on two small ball bearings with the grease removed to lower the friction.  The pendulum rod was printed in two sections and epoxied together with a threaded rod sticking out the bottom.  The finial below the pendulum has an embedded 8-32 nylon friction nut for adjusting the pendulum length.  One eighth of a turn adds or subtracts 10 seconds per day.  It is easy to fine tune the accuracy to within 1-2 minutes per week.


The total print time for all of the components is around 75 hours and maybe a bit less than one spool of filament.  The weight shell...

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  • 8 × 6x3/4" wood screws
  • 10 × 4x1/2" wood screws
  • 2 × 1/8x3/8x5/32 bearing for pallet
  • 1 × 8mm brass shaft for weight drum 2.7" length
  • 1 × 1/8" stainless rod 10" total length

View all 16 components

  • 1
    Design Details

    Here are some details about the clock design and gear ratios used.  Let's start with the naming convention used when designing the clock.  There are eight gear sets labeled mostly starting with the escapement labeled as gear 1.  I suppose the pallet could have been called gear 0, but I simply call it the pallet.  The rest of the gears are labeled sequentially towards the weight drum.

    Here is a diagram showing the clock gear connectivity and speed.  The weight shell has a pulley, so a 52" drop unwinds 104" of cord.  Gear 8 rotates once every 6 hours.  Each gear in the train rotates slightly faster, until it gets to the escapement rotating every 39.5 seconds.  Gear 5 and 6 form a secondary path for the minute hand to drive the hour hand.  There are two 18 tooth pinions on gear 4 with a friction fit to allow setting the time.  

    The gear thicknesses and clearances were defined using the following mockup.  Most gears are 0.2" thick.  Gears 7 and 8 have the most weight on them, so they were made thicker.  There are two 608 skateboard bearings supporting the weight of gear 8.  The escapement and pallet were also made slightly thicker to provide a larger wear surface.  The pallet has tiny ball bearings to support the weight of the pendulum.  I experimented with several different sized bearings and picked a size that allowed a pendulum to "free swing" the longest.  The load is significantly below their design limit so I am expecting them to last a long time.

  • 2
    Power Gear Assembly

    This section shows the process of assembling the gears into the frame.  There are a few preparation steps that need to be completed before assembly.  For now I will just leave it as "print everything and cut the axles to length".  More details to will be added later.

    The build in the next few sections shows a rough rendering of the clock in 3D form.  One of my long term goals is to learn photo-realistic rendering in TurboCAD to make the diagrams even better.

    Start with the back frame.  The standoffs and keyhole hanger should be attached to the back of the frame as the first step.  The picture below shows all of the axles in place, although they will get placed as each gear get added.  The standoffs are not shown, but they would position the frame 1" away from the wall to provide clearance for the pendulum.

    The gears should be assembled starting from the bottom gear to the highest to allow clearance.  Gear 4 with two 18 tooth pinions is the first one.

    Followed by the ratchets.

    And the weight drum (after inserting a 608 bearing into the pocket).

    Oops, I just realized that the image above shows the 4-day weight train with a 44:34 gear ratio and a 1.1" winding drum.  After fine tuning the design, I was able to switch the gears to a 54:24 gear ratio and a 1" winding drum to provide an 8 day run time.  Swapping out the two gears is all that is needed to switch between modes.  The assembly instructions are the same.

  • 3
    Escapement Assembly

    The next step is to work towards the escapement.  Add gear 3,

    Gear 2,

    The escapement,

    And the pallet.  The pallet shaft sticks out the back of the frame for attaching the pendulum.  It also has two 1/8x3/8x5/32 bearings.  

View all 4 instructions

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Discussions

ericcherry wrote 3 days ago point

Awesome looking work! I look forwards to getting the chance to print one of my own once you've shared with us.

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Steve wrote 3 days ago point

Thanks for the positive comments.  I can't make any promises on the time frame for posting the design.  It is a bit too complex to just throw out some STL files and say "good luck".  I want to write up some assembly notes and clean up a few minor design details first.

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ericcherry wrote 3 days ago point

I'll be waiting and watching! I've been casually (really casual) researching how to make the anchor and escapement. Biggest hurdle I've come across is finding some decent documentation on the geometry of drawing them. Been fun, some mild trial and error, mostly error. For a 700+ year old invention they are still difficult guarded castles to get into!

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Steve wrote 3 days ago point

I know what you mean about the hidden info, Ericcherry.  I let Gearotic handle the escapement design, but still ended up modifying it slightly.  The pallet arms worked better when they were lengthened slightly.  At least a 3D printer makes is easy to do iterative experiments.

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L W wrote 3 days ago point

Great aesthetic! 

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Steve wrote 5 days ago point

Thanks, it has been keeping me busy for a while.

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Lutetium wrote 5 days ago point

Nicely done!

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