Pendulum Clock

The goal was to create a compact, reliable, accurate and easy to build mechanical clock without any extraordinary modern or futuristic design and shape so they both look nice and have good readability as a common wall clock for your living room.

I designed this clock with respect to a classical concept of mechanical pendulum clock: 8 day run time, a pendulum hanging on a spring, cyclodial gears, Harrison mechanism, number of gears and their ratio. Many aspects of the design come up from more than 60 years old book.

All parts should be easy to print and I tried to use as much 3D printed components as possible and if not (such as ball bearings and springs), use some common and not expensive components.

Properties

• Seconds pendulum
• Graham escapement
• One week run time with 79 cm drop (11.3 cm per day); designed as 8 day
• Cyclodial gear design (their approximation to be exact): this is standard in most of the regular clock (note that almost all clocks online use standard involute gearing that is not best for clocks)
• Harrison mechanism: no need to stop the pendulum while winding
• Accurate time: error up to 30 s per week or better
• Customizable clock face

Before printing

Required or recomended tools and parts

If you have access to a common workshop (at home) you should be totally fine.

• 3D printer - build size at least 200×200 mm
• Filament - PLA
• Vice/press/hammer especially for pressing bearings into place
• Pliers
• Files for finishing parts (should be needed only for finishing the pallet, but usually you need them here and there…)
• Standard printer and stick glue (like Kores) for printing clock face
• Weight (about 1.5 kg + a few hundreds grams for the pendulum) - steel balls, bolts,…
• Drill and glue if my tolerances don't work for you…
• Hacksaw and files or a lathe and a milling machine if you make the main shaft out of steel
• Patience :)

Required parts

• Ø1.4mm steel shafts or nails (32mm) (or 1.5mm with drillbit…)
• Ø0.6mm nylon fishing line (or a bit thinner)
• 3x 608 ball bearings
• Ø6mm wooden rod (1m)
• 7 pen springs (~Ø4.5 mm × 20 mm): 6 for Harrison mechanism (but it will work even with 4-5) and 1 for hands mechanism.
• Small (steel) hook made out of steel rod (~Ø3mm) for hanging the weight (but not necessary, you can hang the weight by a string directly)

Cut the nails (or rods) according to this table:

*3 gear shafts can be made as one part 36 mm long.

Fishing line: roughly 2 m for winding and about 50 cm for the weight (here you can use regular string/cord). I recommend using an “eight knot/loop” whenever is a knot or loop needed.

Ball bearings: Be sure they are clean, without too much grease (you should be okay without any grease).

Wooden rod: Cut it to approximatelly 98 cm, it very much depends on your pendulum weight. It is a good idea to first cut it into a longer piece (or don't cut it at all if you already bought a 1m long rod). Only if the sliding mechanism doesn't allow you to set pendulum position, reduce the rod length even more.

Printing

I designed this clock for printing with standard 0.4mm nozzle. However, priting small parts with smaller nozzle diameter is a good idea. Use your standard settings, don't print too fast. Print gears and smaller parts at lower layer height (0.12 or 0.1 mm).

All STL files are in mm.

You can choose among different dial versions:

Or create a custom version for yourself by editing one of these (same for the numerals and hands).

You can also choose whatever color combination you like, I personally like one color for gears and different for other parts.

Figure: Shaft nominal dimensions.

Slicing gears: Be sure to always check a printing path! In case it looks like this:

check “avoid crossing perimeters” in Prusaslicer. This will probably cause stringing and bad surface finish, you really have to prevent this. Good result should looks like this:

Also disable thin wall detection if it looks like this:

Good slicing:

Another challange is to print without elephant foot, that will cause incorrect tooth geometry and larger friction. Feel free to play with elephant foot compensation and maybe set value a bit larger than usual.

Slicing skeleton: Use at least 4-5 or even more perimeters, otherwise you will have issue with bending and low stiffness.

Printing the escapement wheel: Be sure, that teeth are not wider at the tip, good result should look similar to this picture:

Post processing

Only the pallet needs to be really post processed (until you print the exact version on SLA printer). To make this process easy, I modeled a tool with the exact dimensions. Make the faces smooth and flat. No burr should be there. Finished pallet should look like this:

Assembly

Cross section for a better idea:

Step 1: Preparing the skeleton

• Press 608 ball bearings and insert glue printed bearings (not much so u can change them in the future) into middle and front plate.
• Mount front cover on front plate with 8mm shafts.
• Press 10mm shaft for hand mechanism to the front plate.
• Attach large pawl and its stop to the middle plate using 10mm shaft.

Step 2: Main shaft

• You need about 19 · π · 30 mm ≈ 180 cm for winding, additional 20 cm (some part still hanging even when the weight is fully winded) + additional length for creating knot and loop, cut a 240 cm piece of fishing line for now.
• Make a knot at the end of fishing line and push it through the hole in the drum.

• Assemble the main shaft, use 2 20mm shafts.

Step 3: Minute shaft

• Use 2x 25mm shaft.
• Insert pen spring between the parts.
• You may use a small handle (Small_handle.stl) for easier screwing and tightening (but don't overtighten the thread).

Step 4: Third shaft

• Use 15mm and 8mm shaft (or one long shaft).

Step 5: Escape shaft

• Use 15mm and 8mm shaft (or one long shaft).

Step 6: Pallet shaft

• First press two 14mm shafts - pins into crutch (Crutch1.stl) - these two will touch the pendulum rod. Then make whole crutch by connecting Crutch1.stl and Crutch2.stl with two 8mm pins.
• Attach two 8mm shaft pins to the pallet shaft (or once again use one long shaft).
• First screw the pallet into place, than the crutch (you can tight the crutch just enough so you can change its angle in the future (but you cannot set the position very precisely this way)).

Step 7: Place the shafts into place

• Now put all pre-assembled components with the back plate and covers in place as in the following picture. (A bit tricky is to place pallete shaft with long crutch so start with this component.)
• Make sure the large pawl is in its place and does not hang elsewhere.
• The most difficult part is to put in place the front plate, because you have to put into place all the shafts at one time.

Step 8:

• Secure the front plate with four pins.
• Put on the hand mechanism.

Step 9: Finishing the body

• Put on the dial and hands.

Step 10: Pendulum

• First put some weight into the pendulum, then put the connector inside and close the pendulum with the cap. After that press in the wooden rod from one side and screw threaded rod from another side.
• Press the hook onto the wooden rod in the right angle, so the pendulum bob is in the perpendicular to the cutout in the hook.
• After that screw the regulating nut on the M6 rod.

• Put two 10mm pins into the pendulum spring and put it into the frame. Than hang the pendulum so the rod is between two crutch pins. Try holding the pendulum rod in one hand and using your second hand to hit the spring.

Step 11: Weight

• Weight assembly should be fairly easy, but first you have to make a string with two loops. Then push it through the bottom piece, put on the tube (I made one just out of rolled 1mm thick A4 paper wrapped by a thin one with some texture on it - see pdf in files), put some weight in and close it using the top piece.
• Now complete the pulley.

Step 12: Winding handle

• Complete the handle.

Finally push the fishing line through the pulley and make loop at the end (don't cut it yet, you may find out that you need to move the loop a bit further). Hang the loop onto a small stump on the front plate (from behind).

Setting up the clock

Hanging the clock

Hopefully, modeled keyhole should work just fine as it is common way of hanging stuff on a wall. Now you can hang the weight on the pulley and wind the clock by rotating the handle clockwise.

Time

Just carefully push the minute hand to set the time. Try moving only forward, because moving hands backwards might stop the clock.

Beat - The Tick-Tock sound

First of all, don't care about your pendulum length. You have to make your clock create regular tick tock sound. If you hear something like “ticktock-pause-ticktock-pause” move/rotate your clock slightly until you hear the regular sound.

Is your clock running? If so, congratulation! (If not, see issues below) Now you want to make your clock run accurate. To do so, longen or shorten you pendulum with adjusting nut at the bottom of the pendulum bob. You can use trial and error method or if you want play with math yourself, just use this well-known equation (linear aproximation for small angle)

where T=2 s, g~9810 mm/s^2 (for Czech Republic) and l is the length (in mm). To make this process easier, you can use my short script in COLAB, which uses the expression above (currently only in czech language).

Possible issues: Your clock is not running or you have similar problem. Don't give up. The issue is ussualy one of the following:

• Clock is running for a while and then it stops: Too much friction or too light weight. Check your gears, they must rotate freely. Maybe try adding a bit weight.
  Another possible issue is that your crutch is “knocking” on the pendulum rod because of (small) space between two crutch pins. This causes loss of power and even stopping the clock.
• Escapement doesn't work at all: Check the escapement wheel, the teeth might be too wide, try to make the teeth thinner/sharper with a file. Also check your pallet if the shape is correct.

Conclusion

That's it! Your clock should be running. I hope you like my design.

In long term of use, you may have change the pendulum spring from time to time just to be sure it won't break if it is made out of PLA (I haven't tested it for long enough time to be sure it will last). The best way is to make this spring out a different material, the best option is to use thin hardened steel as this is the way of hanging a pendulum in regular clock.

In the future I may add more versions of the dial or/and create a version including a second hand.

If you like my design, please consider a donation.

EDIT (02.01.2022): Design with second hand is now included.
EDIT (15.01.2022): Added STEP files of the clock dial and hands so you can modify its appearance.
EDIT (15.01.2022(2)): Fixed clock dial files.