Question about gearing

Hi everyone. I've been a long time lurker, and I love the site. I've learned so much just by coming here. I've just registered to say you have inspired me to take on a project of my own.

I've sort of hit a bump in the road, though.

I have an idea for a clock. I want to do a steam-punk flavored wall or desktop clock with exposed brass gears and various and sundry bits I have laying around.

I want to tack the numbers directly onto the gears and use them instead of hands. So one large gear on the left with the numbers 1-12 in place of an hour hand, one large gear on the right with 00-55 by fives for the minute hand and a gear under the two that counts off the seconds.

So, if I can get a motor downgeared to 1 rpm to drive the "second gear" I'd need a 60:1 gear ratio to make the "minute gear" accurate, and then 12:1 off of that to do the "hour gear."

I know I can't drive them all directly off each other, because that would make the "Second Gear" tiny and the "Hour Gear" huge.

Where I'm stuck, aside from my poor math skills, is how to get the ratios right and size of each intermediate step and number of teeth, etc.

I don't know enough to tell if I'm in over my head, but it seems "do-able" from my perspective. I'd appreciate any feedback you all could give, even if it's just a link to a tutorial that will get me started. I'm not on a deadline or anything, I just found the urge to make something cool.

I have a bit of a budget if I need to have something custom fabricated, but I'd prefer to do as much of it as I can. I wouldn't mind using off the shelf stuff like bicycle gears or similar, because I could always have them engraved and plated and made to look cool.

So, any help or nudges in the right direction would be appreciated.

Thanks in advance, and thank you for such a wonderful site/community.


**edited to add***
Of course I'd be delighted to write an instructable about it when It was done. It would only be polite. ;)

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lemonie6 years ago

Mechanical washing-machine control units run slow. They're very expensive to buy, but cost nothing if the device is junk.


CameronSS6 years ago
Would it be easier to just get a high-torque clock movement and attach things directly to that as though they were hands? I imagine that well-balanced gear rings wouldn't be much harder to turn than giant clock hands, particularly if you lightened them up (e.g., hollow out the back, use light materials, etc.) The problem with a gear motor is that it won't keep terribly accurate time. If it's run off batteries, you'll need some electronics to drive the motor at a constant speed as the batteries run down. If it's run off mains power, it'll tend to be simpler, but again, the accuracy of the speed will be affected by the frequency of your wall outlet, which is rarely exactly 60Hz (or 50Hz in some heathen places), and can swing by up to a few Hertz, depending on the load on the power grid--the wrong frequency means the motor may not turn at the right speed, so you'll have a slightly variable-speed clock. I say all this as though I have experience building clocks. I don't.
IggyPiggy (author)  CameronSS6 years ago
Ah, I see what you are going for. I was planning to have the "hand gears" be side by side (with the "second hand" gear below them, rather than stack them on top of one another. Which I admit would be much simpler. I was going to have it "spread out" so the various connecting gears and chains and things were exposed; it feels more "steam-punkish" to me. I'm also not terribly worried about horological accuracy. Pretty is more what I'm shooting for. Again, I have very little experience with problems of this sort, so I have no idea how over my head I am getting. I have a few sketches I'll try to figure out how to post to see if I can make my ideas clearer.
IggyPiggy (author)  IggyPiggy6 years ago
This was my inspiration, I just wanted to add a "Second Hand" gear and change the layout a bit for ascetic reasons. But the basics, the side by side gears instead of hands, is what I'm looking for. https://www.instructables.com/id/Gear-Clock/
Okay, I was imagining something like a planetary gear clock, although I'll point out that you could still use clock movements, it would just take three of them. :P

Here's my thought: Use the ratios from that Instructable to drive the hours wheel from the minutes wheel, which leaves you with getting power from the 1RPM motor and seconds wheel to the minutes wheel. If you put another identical 12:1 drivetrain in, and connect that to a 5:1 gear train, it'll total a 60:1 ratio. Or if you want more equal-size gears, modify it to a 10:1 and a 6:1 ratio. Or if you want less equal size gears, modify it to a 15:1 and a 4:1 ratio. Or 20:1 and 3:1. Or 30:1 and 2:1.

Hope that helps a bit.