Forum Posts

David Elworthy
Jan 10, 2022
In Printed Clocks
I've noticed something at seems odd about some parts of the gear train. Here is what I expect to see at the interface between gears 5 and 6 (6 = final gear driving the hour hand): Gear 5 is turning anticlockwise pushing gear 6 clockwise. But often when I look at this what I see is the following: The teeth of gear 6 are just resting on those of gear 5 inner, with the wrong faces in contact. I can manually nudge gear 6 anticlockwise so that it is on the correct face of the gear and it will then flop back into this position. If you look in the background, you can see the same thing is happening between gear 4 and gear 5 outer, and this is likely to be the root cause of what happens between gears 5 and 6. Eventually gear 4 advances enough to engage with the correct side of the teeth on gear 5 outer, and gears 5 and 6 also correct themselves. For a minute or two before it fully engages, you can see gear 5 bounce on each tick. I am still affected by the stopping problem every few weeks so I'm trying to look for anything that could be anomalous; I've already changed the parts from silk PLA to regular, checked the bearings, polished the arbors and dry-lubricated everything, and increased the weight, and I still get this problem. If you have any thoughts about this, let me know!
10 day clock - strange gear behavior content media
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David Elworthy
Nov 29, 2021
In Show and Tell
This is my latest clock: https://www.youtube.com/watch?v=dR3y-6C9Yx8. Based on William Strutt's epicyclic gear clock from the 1830s, with a guest appearance from Ferguson's Mechanical Paradox.
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David Elworthy
Nov 08, 2021
In Debug Hints
I thought you might like to hear more about my experiences with the stopping problem. I built the 10 day clock in August, and had it run reliably for around 5 weeks, after which it began occasionally stopping. Eventually it got to the point where it was stopping twice or more per day. We discussed this a bit at myminifactory and on discord, and I decided to reprint everything using regular hatchbox PLA instead of silk PLA. When I rebuilt the clock, I also re-cleaned the bearings and lubricated them with dry PTFE, and picked the best ones by spinning them on a 3mm shaft and counting how long it was until they stopped. After reassembling the clock it ran with less weight than before (down from about 7.5 pounds to 5.5 pounds). The pendulum swing was +/- 3 degrees most of the time, occasionally a little less. It ran reliably for 14 days. This morning I noticed the swing was only +/- 2 degrees. From when I set the beat originally, I know this is about the minimum that will work. This evening, the clock stopped. I noticed that if I restarted it with the pendulum swinging ~5 degrees, it decayed back down to 2 within a minute or so. I've just tried removing the pendulum+anchor and its arbor and reseating the bearings. Spinning them on a 3mm shaft as before showed they still run for as long, so I don't think they need further cleaning or lubricating. I also noticed the dial had a little (tiny amount) play due to some unevenness in the top of the base, so I sanded the top of the frame to smooth this out. Too early to tell if I've fixed the problem, but after an hour the pendulum is still showing a healthy 3 degree swing without quickly decaying to 2 degrees. Not sure what to make of all this. It eliminates silk PLA as being the problem for my clock. I've noticed that bearings are a loose fit in their hole (likewise the arbors), and this is something which can vary from one printer to another. We'll see what happens over the next few days (weeks? hours?). I did rewind the clock just 2 days ago, and it makes me wonder if this might shake the bearings out of alignment causing extra friction. It would only take a little extra to cause problems. The first half of this video (https://www.youtube.com/watch?v=FKpRrlZuuZo&t=88s&ab_channel=woodentimes.com) has some observations about the effect of misaligned bearings. If it stops again, I think I might try putting a little shim round the bearings to hold them in place better. I've done this on other projects by sticking a tiny piece of tape round the rim. Maybe polishing the arbor more would also help. I'm interested in any thoughts about all this.
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David Elworthy
Oct 26, 2021
In Printed Clocks
What do you think is the smallest workable size for printed gears? I am starting work on a design and due to various constraints, it would require a pinion with 8 teeth and a module of 1.2, giving the gear a pitch diameter of 9.6mm. I know I can accurately print it that small, but would it be too fragile or have other problems? I read something which suggested 9 teeth was about the limit (at a 25 degree pressure angle)
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David Elworthy

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