Linear Clock Ratchets Up The Action

On the face of it, making a clock that displays the time by moving a pointer along a linear scale shouldn’t be too hard. After all, steppers and linear drives should do the job in a jiffy. Throw an Arduino in and Bob’s your uncle, right?

Wrong. At least that’s not the way [Leo Fernekes] decided to build this unique ratcheting linear clock, a brilliant decision that made the project anything but run-of-the-mill. The idea has been kicking around in [Leo]’s head for years, and there it stayed until inspiration came in the unlikely form of [This Old Tony], one of our favorite YouTube machinists. [Old Tony] did a video on the simple genius of latching mechanisms, like the ones in retractable pens, and that served as an “A-ha!” moment for [Leo]. For a ratchet, he used a strip of bandsaw blade oriented so the teeth point upward. A complex bit of spring steel, bent to engage with the blade’s teeth, forms a pawl to keep the pointer moving upward until it reaches the top.

[Leo] decided early on that this would be an impulse clock, like the type used in schools and factories. He used a servo to jog a strip of tape upward once each minute; the tape is engaged by jaws that drag the pointer along with it, moving the pawl up the ratchet by one tooth and lifting the pointer one minute closer to the top. The pointer releases at the top and falls back to start the cycle over; to arrest its freefall, [Leo] had the genius idea of attaching magnets and using eddy currents induced in the aluminum frame for the job. Finished off with a 3D-printed Art Deco scale, the clock is a unique timepiece that’s anything but boring.

We really appreciate [Leo]’s unique and creative take on projects, and his range. Check out his everlasting continuity tester and his phage-like sentry gun for some neat build details.

14 thoughts on “Linear Clock Ratchets Up The Action

  1. That is a very cool idea. Pretty and useful.

    I wonder if the blade tips could be annealed while not warping the blade just by clamping it between two steel bars and heating with a torch etc..
    That said so many saw’s these days have coated blade tips making the steel softer won’t actually work – the ceramic diamond etc coatings don’t soften.

    I think for myself I’d just add a little depth to the spring saw interface – a hardox? wear plate in effect – few weeks of sawing slowly through such hard material should blunt the blade enough to just let the spring run on it again…. Or perhaps send the tip out for ceramic coating – not sure it would take the rather hard shock nature of the mechanism but it would greatly reduce the wear.

    final idea to solve that would be to use multiple blades so the teeth are very very much wider – same cutting force but over a vastly larger area should reduce the wear too.

  2. Instead of interfacing the saw blade with the spring wire directly, one could just cut a smaller section of saw blade and attach it to the end of the wire with the tooth direction inverted, giving you a positive latching interface of equal hardness.

  3. If you like latching mechanisms, look up “Castro Viejo Needle Holder”. It’s a surgical instrument for holding a needle for suturing. Squeeze the handle once and it locks shut, holding the needle tightly. Squeeze again and it unlocks, letting go of the needle. It makes a very satisfying click with each squeeze. Real surgical use ones cost $300-400, but you can buy cheap ones for about $10.

    I use them (the real ones) for suturing my patients occasionally and love how easily it handles compared to the traditional needle holder that looks a lot like a hemostat.

      1. You’ll love using a needle driver- the jaws are knurled, so whatever you grip with it stays in the position you grabbed it in. Hemostats have linear grooves and everything you grab, like a component lead wire, will rotate until it drops into one of the grooves.

        Cheesy needle drivers have smooth jaws – make sure whatever you get has knurled jaws. Last year I bought a “German steel” Castroviejo needle driver with knurled tungsten carbide jaws for $15 via ebay. I don’t know what “German steel” means, and I don’t know if the jaws are really made of tungsten carbide, but it works well and most importantly, the hinge seems to be good. You can find cheaper ones if you skip the tungsten carbide jaws…

        This video will give you a sense of the satisfying click it makes:

    1. Also, I totally agree that the servo sounds terrible and solenoids are just as bad. There must be a graceful way to do this, either with an actual clock spring (a big one) or maybe a really low pressure pneumatic arrangement whose tank gets recharged very slowly by a much reduced gearmotor. Fortunately time is on his side when it comes to re-pressurizing :-)

      1. The big solenoid might well not be heard at all – if used as he suggested to tension the spring it quite possibly doesn’t hit its endstop in the active pulse – so no clack there – and then is being pulled back to the start by the same spring that pulls the carriage – high enough load to lift it probably won’t do it with great gusto either..

        Almost certainly hear the relay firing to trigger it though, no matter what you do to the rest relays always seem to be damn loud..

  4. I like it, but I had a different idea for a clock, a water clock with the display on a vertical stick moved by a float in a Pythagorean cup, have water drip into the cup to fill it over 12 hours, raising the display stick (with an arrow on the cup pointing to the time) and when it reaches 12 hours it overflows the siphon and WOOSH, clock reset and the time starts over again.

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