The Horological Dilemma - Bring Your Genius!

Every once in a while, somebody will email me a question because they think I'm smarter than I actually am. Now, while I'm no drooling idiot (opinions may differ), there are some things that are far beyond my ken. So, when Phil emailed me with the question below, after I lay down for awhile, I thumbed through my rolodex of geniuses (that's right, rolodex. Hey, Laugh it up, but when a giant electro-magnetic pulse destroys all the computers on earth, don't come looking to me for help.) and found Steve Hoefer's email.

"I'm interested in French Revolutionary Time. Basically, they wanted a base ten time system. In other words, instead of a 24 hour day, just make it a 10 hour day. Noon is no longer 12pm, it's 5 o clock. I'm imagining a 24 hour clock rotation plus a custom clock face. (Great example:
Making a clock to these specifications would probably be pretty straight forward, but I can't find anything like this online. Any thoughts?"

I knew this was just the kind of problem that would intrigue Steve, and I wasn't wrong. As I watched the emails fly back and forth between Phil and Steve (an experience not unlike watching a Russian action's really exciting, but you have no idea what people are talking about), I asked them if they'd be interested in opening up the discussion to the DudeCraft readers and seeing what might happen. They were both enthusiastic about the idea, so now it's time to put your thinking caps on. We need to make us an analog, French Revolutionary Clock, stat!

Steve, being the head genius in charge of this project has been kind enough to say that he's willing to take care of the comments section for this post and let me get back to what I do best...very little.

Ready? Go.


  1. Would be very popular if you explain that people will be working fewer hours. - Steve B.

  2. Alternatively, re-program a clock kit like this one might be the easiest way forward to start


  3. The Bulbdial kit is fantastic! And definitely up there for looking great and being easy to modify. (Another option along those lines is the Monochon: )

    During the email exchange with Phil we decided we'd really like an analog display with physical rotating hands. (Fitting for a time system devised 200 years ago.) This makes things a bit trickier and I still haven't through of an ideal solution yet.

    Great thoughts so far, keep the ideas coming!

  4. So, I opened up one of those standard wall clock mechanisms (runs on a single aa) and counted the teeth on the eletromagnetic drive

    Guess how many? (o;

    All you simply have to do is grow really steady hands and cut a new cog with 10 teeth. Shouldn't be too hard

    Now the only fly in the ointment is that I made a big assumption that because that first cog has 12 teeth and it drives everything else, the math is obvious. I did note that the electromagnet turns that cog in either 90 or 180 degree steps (I couldnt quite make it out) and I have had enough coffee to figure out if that's important.

    But, that's where I'd start hacking at this problem. cheers /pauric

  5. Just realised that no, the 90 or 180 rotations of the master cog is not important and reducing the teeth will not affect the total travel of the hands. Reducing the number of teeth on the master/drive cog reduces the number of steps but increases the speed of the hands (as long as everything else is constant).

    I hope my thinking is sound, still need some coffee.

  6. Hooray! There's already a bunch of junk I don't understand! But like that Russian action movie, I'm really excited about it! Keep going!!!

  7. Well, the simplest method would probably be to replace the dial with one that reads from 1 to 5.

  8. Thanks for doing all the legwork and the photos Pauric!

    Wow, those gears are small, though I suspect a steady hand or possibly a laser cutter could make a modified replacement.

    After pondering the project a bit more the problem isn't really the hour hand. There are 24-hour clocks that go around once a day, as Steph says replacing the dial would be simple.

    The trouble comes with the minutes and seconds. A decimal minute is about 40% longer than a traditional minute while the seconds are a bit faster. So now that we have an hour hand that runs the right speed, can we get a minute hand that runs slower?

  9. ...but if you want a 24-hr rotation you'd need to *double* the number of teeth on a wheel (of the same size) to make the hands go at half-speed, and get a new pinion with smaller leaves to fit the half-sized teeth.

    then you can add a dial that reads from 1 to 10.

  10. a clock movement is a closed system ie the hour, minute and second hands are connected by their gears and turn relative to each other. their mathematical relationships are already there.

    so if you get the hours right, the minutes and seconds should follow.


    chapters 1 and 2 give you an idea of the math and how the gears fit together

  12. Ooh! Ooh! Build one! Time lapse video. Build one! Time lapse video!

  13. ah, yes, you're right about the minutes/seconds problem, in terms of modifying a 12 or 24 hour clock.

    so it'd be, what, 100 minutes in an hour (and 100 seconds per minute)?

    it'd probably be easiest to build a clock from scratch... out of wood.

  14. Thanks for the links Steph! (I could definitely use a practical course in horology. I think I'm getting one in this comment thread!)

    For a decimal and traditional 24-hour clock the hour hand does indeed move the same speed, going around once a day. That gives us a great reference point.

    The minute hand needs to rotate 1000 times a day (10 hours x 100 minutes and hour). While a traditional clock's minute hand goes around 1440 times. (24 hours * 60 minutes). Likewise the second hand should rotate 100,000 a day vs 86,400.

    Now off to read up on gear ratios to see what I can discover!

    Keep the great stuff coming!
    (And thanks to Paul for hosting this discussion!)

  15. Some of my smart Twitter followers found this great resource for calculating and making wooden gears by Matthias Wandel:

    (Be sure to check out the other stuff he makes, especially his fantastic marble machines.)

    Thanks to Evil Mad Scientist Labs (@emsl) and Pauric (@radiorental) for the link.

  16. If you're not interested in building a mechanism from scratch, amateur-radio supply stores sell 24-hour clocks - it might be worth starting with one of those mechanisms. For instance, there are several at (I don't work for there, but I've purchased from them in the past).

  17. Great link Len! In my 'net search I had seen some photos of 24 hour clocks, but never found them for sale. Knowing they're related to ham radio operation gives it a whole other dimension, and another great thing to learn about.

    Thanks for sharing!

  18. Great comments. Thanks everyone!

    I just came across two "metric clocks" from cafepress. No real information about either so I assume the minute- and second-hands are both "off."
    Anyway, at 15 bucks a piece, and an already prepared face, it may be a cheaper way to get to the finish line. I don't _want_ these clocks to be perfect metric clocks though. It's too much fun as a thought problem to have such a simple buy-your-way-out-of-it solution.,3466246,30924592