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It takes a surprisingly small amount of friction near the escapement to stall the gear train when there is around a 500:1 gear reduction. My guess is to look on the right side close to the escapement.

The debug steps should be listed in the assembly guide. Here are the important ones:

Every gear must be drilled to be loose on the arbor.

Every gear needs to have some end shake after assembly into the frame.

The gears that pass through the frame need to rotate freely. This would be gears 6 and 9 on this clock.

Gear 3 behind the escapement is connected solidly to arbor, so the arbor must rotate freely inside the frame.

If all of these checks pass, then start removing gears one by one to see if you can identify the trouble spot. Start with the escapement, then gear 2, 3, and 5. You may need a spacer to hold some of the gears in position along the arbor for some of the steps.

Quick followup: My SP13 has now been running continuously for 6 days, with no signs of stopping. I assembled the drive weight with pulley and enough shot to give 4lb 5oz. This is less than the safety margin recommended by the instructions, but it's been running so well, I'm inclined to leave it alone for now. The pendulum swings just a hair over 2° each side. I adjusted the pendulum four times since making the drive weight, and think I now have it very close. I have not touched it in the last three days, and it's still within 30 seconds of true. Very happy with the design.

-Matt

That is interesting. I have purchased those screws in the past and don't remember the heads being oversized so much. There is a lot of variability between brands though. An 82 degree countersink is a quick solution. This trick should get added to the assembly guides.

I order screws for the parts kits from McMaster-Carr, product number 90048A151. They are specified to have a head diameter of 0.262" and usually measure close to 0.25". I keep using them because they are extremely consistent across many orders.

The parts kit can be found at https://www.etsy.com/listing/1680180262/sp4bsp5b-easy-build-clock-parts-kit

Thanks for the kind words. A lot of effort goes into optimizing a clock for 3D printing.

The horizontal form factor of this clock stacks gears on a single arbor that can be a bit sensitive, as you found out. Once it is adjusted, the clock should run great.

Regarding pendulum length, many old clocks have a 2 second period with 1 second in each direction. This often used two gear pairs with 60:8 and 64:8 ratios followed by a 30 tooth escapement and a 39" pendulum. I believe that a 39" pendulum is disproportionately long in a small clock.

All of my clocks have shorter pendulums. This requires different gear tooth counts. For example, gear ratios of 36:8, 36:8, 36:8 and a 25 tooth escapement has a 24.5" pendulum beating 4556 times per hour. In the days of hand cut gears, the 39" example has 170 teeth to cut, while the 24.5" pendulum only has 157 total teeth and an additional arbor. With a 3D printer, the total number of teeth is an insignificant factor. I select gear ratios that allow a good overall balance. There is no difference in accuracy of a 39" pendulum compared to a 24.5" pendulum.

That is the first time hearing anything about the click screws rubbing. Flat head screws should sit nearly flush and have enough clearance. You have a solution that also works.

The pendulum support bearings are easy to check by running the free swing test. Anything greater than 10 minutes should be OK.

The escapement characteristics after the clock stops can tell you a lot about what to debug next. Does the escapement still spin? If not, then look for defects on the gear teeth where they are meshing. Also check for end shake on all the arbors. If the escapement is sluggish, then look for friction. Make sure every gear spins freely on its arbor.

You need to hold the clock level when running without the pulley. It is a simple way to double the effective weight, but the balance is off so the frame wants to tilt and the clock will be out of beat unless the clock is held vertical.

Your clock should be very close to running perfectly.

I use TurboCAD Platinum 2018 with the faceting quality set to the highest level.

There are probably cheaper alternatives available today that would do an equivalent or better job.

Looks great.

The moon phase operation is only two gears and a friction clutch. Make sure that both gears can move freely. Touch the gears and they should move slightly. Test the friction clutch by manually rotating the moon dial by reaching behind the main dial. There should be a small amount of resistance.

Another possibility is that you need to wait longer to see the moon phase rotate. The moon dial makes one complete rotation every 59 days. This gives a full moon cycle of 29.5 days.