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HELP

by TrevM, published

HELP by TrevM Nov 17, 2012

Description

I am trying to create a fully printable mechanical clock. But I have failed miserably, I can NOT get it to work.

Recent Comments

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did you end up getting it working?
Neat! I've had an idea like that for awhile, but I lack an animal to use it..so..
As for the other comments on here, like I said, I'm dense when it comes to clockwork stuff. My knowledge starts and stops with "it ticks". The one in the video is about 98% 3D printed, spare the screws holding it together and the string.
And your right: I prefer how yours looks!
I may revisit later, but I got side tracked, now making an insert (6 foot x 3 foot) for a patio door that includes a dog flap. Dog flap is motorised, push button or remote control, it also tries to read dog RF ID and uses result to auto open or close it.
Bit complex, lots of electronics, printed gear boxes and counter weights.
But, once that's working then maybe...
The comment below from maurepe was very valid, specifically the part about using metal rods as axles, I am pretty certain that the clock would work with that modification, but it kind of detracted from the 'pure printing' aspect. Though I think mine looks prettier than the one in the video :-)
Aint life a giggle :-)

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License

HELP by TrevM is licensed under the Creative Commons - Attribution - Share Alike license.

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Instructions

DO NOT MAKE IT. IT DOES NOT WORK.

I've just uploaded the OpenSCAD file on purpose. I think I have the involute gears correct. Whole gear chain works, but it is way too tight. I started off with plastic on plastic bearings, tried in ABS, gears seemed to floppy and ABS seemed too abrasive, switched to PLA, much harder, seemed to be close, but too tight. Current file allows for 2mm ball bearings for every gear bearing, better but still too tight.

I'm only a software engineer, I am dearly hoping that some mechanical engineer with OpenSCAD experience could take a look and give me some advice.

did you end up getting it working?
I'll be first to say I'm dense, but I did find this (https://www.youtube.com/watch?v=HgZBPYJ2Y-w) and thought you might be able to take some ideas from it and figure out what went wrong. I would love to take a look at them both and see what wrong, but again: dense.
Erm, I published on Nov 17 2012, youtube video published 7 Oct 2013 (11 months later).
I thought it would be cool, you can't get much older technology than a weight driven pendulum regulated clock and you can't get much newer technology than 3D printing and I wanted to combine the 2, appealed to my sense of humour.
I searched everywhere and did not find a single clock design, so I started this, I could not find gears so I created them, it took me a long time to design and the damned thing wouldn't work, I tried about 5 different ways of doing axles but none were free enough to work, so I published anyway. By the time I published there was a challenge that was completed by Makerbot (as pointed out below), so though I think I could have re-designed it to use metal rods for axles (my original plan was fully 3D printed), it probably would have worked, but it had already been done and I lost interest.
I do find it intersting that this design is clearly marked "DOES NOT WORK", but people still download and collect it :-)
I know. But since the info on this still shows that your trying to get it to work, I figured that to be true, and figured you might be able to see what is wrong with this one based off of looking at that one (nothing rude meant with that, by the way!) I tend to drop a project for months and come back to it, so I figured that might be the same on this.
As for the "does not work" tag: yup! It's always great when people don't fully read the info provided with something they want to use.
I may revisit later, but I got side tracked, now making an insert (6 foot x 3 foot) for a patio door that includes a dog flap. Dog flap is motorised, push button or remote control, it also tries to read dog RF ID and uses result to auto open or close it.
Bit complex, lots of electronics, printed gear boxes and counter weights.
But, once that's working then maybe...
The comment below from maurepe was very valid, specifically the part about using metal rods as axles, I am pretty certain that the clock would work with that modification, but it kind of detracted from the 'pure printing' aspect. Though I think mine looks prettier than the one in the video :-)
Aint life a giggle :-)
Neat! I've had an idea like that for awhile, but I lack an animal to use it..so..
As for the other comments on here, like I said, I'm dense when it comes to clockwork stuff. My knowledge starts and stops with "it ticks". The one in the video is about 98% 3D printed, spare the screws holding it together and the string.
And your right: I prefer how yours looks!
Very interesting design.  You have obviously put a lot of time and effort into this.  You even wrote your own involute gear module(s).  I am not a clock expert, but I think it looks like a pretty solid design that could be made to work with some tweaks.

Here are some things that I that you are doing correctly:
  * When increasing speed with large ratios, it is best to split the change down into several stages, each with a modest speed increase.  You do this well.  All of your steps seem reasonable.  The biggest is 5:1.  If this gives you too much trouble it could be split into 2:1 + 5:2

  * Bigger gears are more forgiving of printing imperfections and allow looser tolerances.  Your gears are nice and large.

  * You have a raised area on the frame, not much bigger than the shaft, by each gear to keep the teeth from rubbing on the frame.

  * You support your gear shafts on both ends.  I noticed to make that printable, you have the "top" of the shaft male and the bottom female.  That should work, but the larger diameters required are causing extra friction. See below.

  * PLA is a better choice than ABS.

Here are some suggestions that I came up with:
  * The friction of the gear's shaft goes down as you decrease the diameter.  It looks like you gears have large diameter shafts.  This will cause a lot of friction as the gears turn.  Consider reducing the diameters of the shafts where sliding contact occurs.  For a first order model, the force of the friction is the same regardless of shaft diameter, but the distance travelled is proportional to the diameter, so the energy lost and the torque are both proportional to the diameter.  This is especially important on the gears closest to the weight.

  * It is often hard to get low friction between to similar materials.  That is to say it is hard to make PLA on PLA bearings.  Especially printed ones, which will never be perfectly round or smooth.  I think it would help your design a lot to use metal shafts (that would incorporate my reduce shaft diameter suggestion at the same time as this one).  The frame and gears would still be printed, but you would purchase metal shaft such as 3/32" brass rod or tubing.  Amazon sells 36" of 3/32 brass tubing for $2.80.
http://www.amazon.com/Brass-Seamless-Round-Tubing-Length/dp/B000FN6920
I have used similar hobby tubing in the past.  It is easy to cut and slides well.  For shafts with more force on them (weight pulley and first few gear stages) you can use 1/8" stainless steel rod.
http://www.amazon.com/dp/B000HZTGBC/ref=biss_dp_t_asn
This is more expensive and harder to cut, but it is probably worth it.  It would not be too hard to modify the design to use the rods.  Put a hole through your gears and the frame and insert the shafts.  I recommend making the hole undersized and drilling it out to the correct diameter after printing.  Be sure to keep a small raised area around the shaft so the teeth don't rub.  If you use the metal rods, it can be much smaller in diameter than you are using now.

  * You could consider more experimental 3D printing materials.  Nylon would be a good fit here because it is strong, tough, and has a low coefficient of friction.  I just saw thing 34801 found a nylon filament that prints at a similar temperature to ABS.  I haven't tried it, but it looks promising.
Thank you very much indeed.
I had no choice but to create the involute gears, there does not seem to be that functionality anywhere else for OpenSCAD.
I really wanted fully printable with as few vitamins as possible, I started with pure friction bearings, then I altered so that I had a 1mm ring making contact within each female part. I finally went to using 2mm ball bearings on every shaft end. So I learned by trial & error that friction was the problem, I had not thought of using metal rod, thanks again.
I have not tried anything other than ABS and PLA so far, I've only been playing with this printer for 4 months.
Hi Trevor,
Have you examined the Makerbot Clock design? You might get some ideas from that. http://www.thingiverse.com/thing:18214
Best of luck with it!
NumberSix
MakerBot Clock
Thank you, I have been searching thingyverse for a fully working clock design, I have no idea why I didn't find the Makerbot one!
So, it has been done, not sure I should bother with this one.
I know it is very hard to make a clock, any gear will work down ratio (fast to slow) but going upratio is very hard, gears have to be correct and bearings have to be correct.
This clock goes from 1 revolution per day (weight wheel) to 1 revolution per 15 seconds (pendulum wheel).
I have tried top assembly with gears 1 thru 7, that works freely under weight power.
I have tried gears 7 thru 14, that works freely pushing lightly with finger.
I have tried top assembly with gears 1 thru 11, that is just slightly too tight, works with weight plus finger help.
But put it all together and no go

The scad file does include pendulum, but left that off for now, whole gear chain needs to be free running first, then I add the pendulum to regulate down to accurate seconds.
I have not included stl files on purpose, I don't want anyone to go through pain of printing just to end up with something that doesn't work.
what about stl files, not everyone has scad. 
I think you need a pendulum....
it may not tell accurate time, but does it at least work? 
Don't feel so bad. Clocks are the pinnacle of mechanical engineering. In the old days, if you were an mechanical engineer apprentice, your final exam would be to design and make your own clock. It is the culmination of years of learning and experience. Keep working at it, you'll get it right some day. Be sure to look at some old grandfather clocks that are working and see how they work. 
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