For a long time, I've had this "dream" to build a grandfather clock. It's something ornate, and valuable, and even useful. it doesn't take up much room, and if done well enough, can easily be an heirloom.
Recently, I bought my first real watch. A Strela TR42CYM which is a replica of the watch Alexei Leonov wore on the first ever EVA mission. It's awesome. And it kick started this new found motivation to research, and build a grandfather clock.
I could easily buy a pendulum movement for the grandfather clock. They're around $300 for a decent one. But of course, I don't like to do any thing simple. Metal working is a medium that I've wanted to try my hand at. And the idea of building a mechanical computer is very exciting. Plus, there are a number of non-standard complications that I would love to have as part of this build, which I can't get if I buy the movement.
The Vision:
I am going to have to figure out how to cut all these gears by hand. It's common to use a mill, and a divider head. But I'm not ready to drop over $1000 just to cut gears. My currently plan is to use my vinyl cutter to out the pattern, apply that to brass sheets and cut them out using a scrollsaw/jeweler saw.
Turns out, brass is very expensive. Before I take a saw to any brass, I'm going to cut a number of prototype gears out of plexiglass, and wood as a proof of concept.Especially the escapement, as I'm fully intending to go through a number of iterations before I get it working.
1. Escapement
First of all, the escapement. The most crucial piece to a clock is it's ability to advance a system of gears at a very specific rate. The escapement is what makes this happen.
The purpose of the escapement is two fold:
1. To regulate the power from the weight so that it is released one second at a time, advancing the gears one second at a time.
2. To add energy to the oscillator (the pendulum) so as to counteract any friction.
A typical escapement has 30 teeth, and is advanced a single tooth per second. This rate is dictated by the pendulum, that should have one swing per second.
If all the escapement had to do was #1, it would be a much simpler device. But since it does both jobs, it must have been a genius inventor who first came up with it. Here is my sketch of the device, drawn to scale.
2. Weight Drive Train
The drive train is the power source for the clock. It consists of a weight, attached to a cord that is wrapped around a drum. This drum is directly attached to a gear. This gear is then connected with a series of gears meant to increase the gearing ratio to about 1000:1 (at the escapement). This means that one single rotation of the drum will happen every 1000 seconds. Without this gear train, we'd end up having to wind the clocks every day. Instead of every week.
With some clever gearing ratios, one can set up the "center" gear to rotate once every hour. This reduces complexity significantly, as the shaft for this gear can be directly (or almost directly) attached to the minute hand.
One last important design feature of the drive train, is the way the drum attaches to the main gear. Both pieces share a shaft, and are pressed against each other. However the main gear has a click, which engages with teeth on the drum. Which allows the operator to wind the clock by merely turning the drum.
3. Hour/Minutes
The hour and minute gear trains have a number of details that make their implementation difficult. In particular, the clock needs to have a "clutch" or some way to disengage from the drive train so that the time can be set. Additionally, the hour and minute hands are traditionally situated co-axially Which forces the gears that convert from minutes to hours to have very specific diameters.
In addition to hour/minute hands, I want separate dials to indicate several other complications. They are: Moon Phase, Star Chart, Equation of Time, and Sunrise/Sunset times.
4. Moon Phase/Star Chart
The moon phase and star chart are actually fairly simple to implement. The star chart makes one single rotations once per 365.24 days, and the moon phase rotates once every 29.53 days (synodic month). Both of these are very easily accomplished by hooking up the correct gear ratios to the hour hand. Unfortunately, my purist attitude dislikes every moon phase dial I've ever seen on a clock. What I really want is a 2 dimensional circle that accurately depicts the phase of the moon, including the gibbous, and crescents. Unfortunately, I wasn't able to find a 2D way to do this. It is however easy to implement in 3D (with a hemisphere shroud that rotates around a moon).
6. Equation of Time
The equation of time is a rare, and obsolete complication that I think is nifty. And because of the nature of the sunset/sunrise calculations, is necessitated. I'll get into this more later.
The Equation of Time is the difference between solar mean time (24 hours, what our clocks show) and the solar time, as told by a sundial. Since the earth orbits the sun in an elliptical orbit, The time between noons (when the sun is right above your head) throughout the year varies.
7.Sunrise/Sunset times
Sunrise/Sunset times are significantly more complicated. Each of these requires calculating sines/tangents/inverse cosines in order to get the correct time. And then, the calculated time is in solar time! Which means a complication for the Equation of Time is necessary for it to make sense. After many difficult hours pondering how exactly to implement these things using gears, I had one break through after another.
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