For a hobby project, I'm designing a clock with a single hand that makes one revolution per year. Using really helpful sites like https://geargenerator.com/, I have the gear ratios and dimensions worked out, and now I'd like to start prototyping.

What's a reasonable way to get some gears made for that? I don't want to spend a lot of money (this is just something to hang on my own wall, probably) but I do want the gears to function correctly.

Is 3d printing a good option for gears, or will they need to be machined? For scale, I think the largest gears will be about 2-3 inches in diameter with around 80 teeth. If machining is necessary, are there different quality options that affect price?

For the curious: my gear ratios are 8:83, 8:59, 8:47, and 8:13. That comes out to 4096:2992067, i.e. 0.5:365.2426 - so a motor designed to go around twice per day (a clock hour hand) should slow down to once per year (including leap years!).

Obviously there's probably some pretty basic stuff I don't know, like whether people usually work with gears in standard tooth numbers or whether weird numbers like the ones I have are accessible.

Thanks for any insight.

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    $\begingroup$ 3d Printer gears are fine, one can reliably make fairly small years depending on module with little effort. Another common option is laser cutting from acrylic or wood. Good luck! (I would laser cut personally) $\endgroup$ Commented Jan 6, 2020 at 13:01
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    $\begingroup$ Don't forget the 400 and 1000 year rules -- you wouldn't want your clock to be off by a day in 2400 (or 3000). To quote Richard Feynman, quoting an old mechanical engineer he worked with during WW 2: "Look in the Boston Gear catalog; use gears from that. Don't use the gears at the top end of the range; they're hard to make. Don't use the gears at the bottom end of the range; they don't work so well. Anything in the middle is OK". To add to that, I'd suggest you try to use as many stock gears as you can, and just have the oddball ones printed. $\endgroup$
    – TimWescott
    Commented Jan 7, 2020 at 21:15
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    $\begingroup$ Another thing to think about is that you could try expressing your ratio as the sum or difference of two ratios that do work out to stock gears. Make up two gear trains and feed them into a differential (which basically adds or subtract rotations). Use the output of that to drive your year hand. $\endgroup$
    – TimWescott
    Commented Jan 7, 2020 at 21:17
  • $\begingroup$ That's a good idea, @TimWescott, I'll see if I can come up with a subtraction of gears that hits the same number. As for the 400 & 1000 year rules - yeah, that's why it's 365.2426 instead of 365.25. =) $\endgroup$ Commented Jan 12, 2020 at 3:51


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