Recently, I have had several clocks slow down and eventually stop running after a few weeks of months of operation. The symptoms are the clock has stopped and manually moving the escapement back and forth does not produce any movement in the escapement. Something in the gear train is completely stuck. Wiggling a few gears or winding the clock a few clicks will often allow the clock to start running again. However, it only runs for a short while and stops again with the same symptoms.
All the troublesome clocks were built using silk PLA because I really like the way the gears look. My best guess is friction as the gears move. The gear profiles are correct, or at least the gears in CAD are correct. Errors could creep in if the gears do not match the expected CAD profile. I will try to find or create a test pattern specifically designed to test the gear accuracy. It could require a change to the extrusion multiplier or XY size compensation. I already have elephant foot compensation under control.
The other consideration is friction as the gears slide past each other. Most of the gear movement is a rolling action with no sliding, but there is always some sliding as the teeth are starting to engage. I printed some small squares of material that allow comparing friction between different brands of PLA. The test jig would have a section with normal PLA next to normal PLA and another section with silk PLA next to silk PLA. Sideways pressure is applied and whichever one moved has the lowest friction.
One thing that was apparent was that lightly loaded PLA of any type has low friction, but friction is much higher when pressure is applied before sliding the pieces. This would be roughly comparable to dynamic friction with a light load and static friction with pressure applied.
I tested 12 different spools of PLA consisting of 3 silk PLA, 2 translucent PLA, and 7 normal PLA. The 3 worst performers were silk PLA, followed by 1 of the translucent, a normal PLA, then the other translucent PLA. The best 6 were normal PLA. Most of the normal PLA brands were difficult to distinguish, but the silk PLA samples were obvious that the friction was higher.
The next step was to replace some failing silk PLA gears with normal PLA gears. The clock definitely runs better, but I can tell that there may still be some issues. I will continue looking for better fixes.
A few other suggestions are to use the shorter runtime options where they are available. I have been running my 32 day easy build clock with runtimes of 8 to 10 days. I am also looking at different tooth profiles with lower friction. I have tested some modified cycloid gear profiles, but they were slightly worse. Involute gears seem to have lower friction in a clock. The next test is to compare different pressure angles to see if one is better than the others. I may also try finer pitch gears where they are closer to the escapement so the pinions can have more teeth.
Let me know if there are any other ideas. I would like to get back to having a fully functional clock with a 32 day runtime. I know the clock works, because I have had it working. However, the high static friction needs to be fixed for the clock to be super reliable. I am looking for a fix.
One thing I haven't seen mentioned here about silk type filaments is the additives they use to create that nice finish. For most filament brands it is a combination of TPE's, polyesters, and lipids. While it makes for a really nice looking finished product, this does mean that things made from a silk type PLA filament are going to naturally be more "sticky" and flexible than ones made from a PLA filament that is made from a purer resin. It also means that the parts are going to be better at resisting wear and abrasion, so maybe the tradeoff can be worthwhile if you're able to design around these differences.
I used CC3D silk antique gold on the gears of SP1. Its been running for 8 months so maybe it doesn't have enough run-time to develop the problem? I did use teflon dry lube liberally on the gear teeth and everywhere that moving parts made contact.
For now I'll assemble SP2 as designed. I could always add bushings later if I wanted.
I expect it's the friction between gear teeth and not bushing friction. My 2 large sp2 clocks are both stopping randomly now after months of reliable use. Both use silk pla.
I have an old sp1 clock that used a different silk pla (can't remember the brand) and its still running fine. I did use dry lube on all gear faces.
Going to pull both my sp2 clocks down soon and do the same.
Hope this helps.
I have built SP1 and so far it is running strong. I just started printing parts for SP2. Would it make sense to go back to the bushings of SP1 in an attempt to avoid this friction issue? If so do you think the smaller arbor holes of SP2 could be reamed for bushings without causing other issues?
I have applied dry PTFE lubricant onto my "big" 21 day clock to try and get it running. The lubricant certainly helped for a while, but sooner or later the clock still stopped.
I have reprinted some of the gears, filed the teeth, increased the diameter of the holes for the arbours but none of this has really helped.
I have printed a total of 4 clocks, 2 big and 2 smaller. I have had more luck with PLA Silk than normal PLA, but this is probablynthe type of PLA SIlk that I buy here in Australia
I am running an experiment now with greased gears. I am using the 32 day EZ build clock with the 10 day gear train and normal PLA gears. The clock would only run for a few hours with an 11 pound weight.
I used white lithium grease with a few drops of food coloring to match the PLA color. It takes a while to mix the water based food coloring, but eventually it appeared to be completely mixed. An old toothbrush was used to add a thin layer of grease to all the pinions and the pallet tips.
The clock is running better than before with a 5 pound weight. I will test how long it runs. Lightweight machine oil or dry lube on the teeth seem like they would have also been a good solution.
Yes. It did help. I have not done a controlled experiment, so I can't really say how long it lasts. I would also consider using normal oil or even a light coating of grease.
Every clock repair book says to never oil the teeth because it will attract dust that acts like a grinding paste and the gears will quickly wear out. The solvent in Teflon dry lube may also break down the PLA, although I probably did add some to my first clock and it is still running for almost 3 years now.
Gears that are sticking are close to being thrown away, so adding any type of lubricant to make the clock work again seems like a good idea, even if it only lasts for a few months.
Have you tried adding a touch of dry lubricant to the gear teeth?
(I'm sure you have :)