Tag Archives: escapement

Watch works

You remember an escapement is a way of slowly releasing energy that powers a clock. A watch didn’t use a pendulum for its escapement—it used a coiled metal mainspring and balance wheel. You wind the spring tightly and the spring wants to unwind. As it unwinds, its energy is released to oscillate the balance wheel back and forth. As the balance wheel oscillates, it swings a little fork side-to-side which stops and releases a gear. This is the watch’s escapement. No matter how the watch is bounced around, the spring keeps on releasing energy at a steady, reliable pace.

The wound-up spring wants to uncoil, to expand. As it expands, it pushes and turns the balance wheel. But the balance wheel is weighted so it only turns so far and then it swings back. When the balance wheel swings back it tightens the spring again. The wound-up spring wants to uncoil, to expand. As it expands, it pushes and turns the balance wheel. But the balance wheel is weighted so it only turns so far and then it swings back. When the balance wheel swings back it tightens the spring again. (Repeat over and over and over and…)




https://sciencing.com/analog-clocks-work-4912745.html
https://www.jcwa.or.jp/en/time/qa/qa07.html
https://www.wixonjewelers.com/education-type/watch-movements/
https://malalan.eu/how-it-works-escapement/
This beautiful video has French narration but the visuals are self-explanatory: The escapement animation starts at 3:30.

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Keep on trying

With John Harrison’s innovations, his clocks were more precise than any clock had ever been. The bad news was: his clocks still weren’t precise enough to win the Longitude Prize. “The amount awarded under the Act was commensurate with the accuracy of the invention in determining longitude: 10,000 pounds for 1 degree, £15,000 for 2/3 of a degree, and £20,000 for 1/2 of a degree.”

Rather than give up, Harrison tried something different. Instead of designing a precision clock, he turned to designing a precision watch. A watch is an analogue or mechanical (not digital) timekeeping device small enough to carry around with you. You can hold one in your hand. People attached an end of a chain to their watch, attached the other end to a belt loop or button-hole and kept the watch in a pocket.

Random side-note: A pocket-watch and chain play a part in the O. Henry short story, The Gift Of The Magi. https://www.enotes.com/topics/gift-magi Spoiler alert! DON’T unlock the summary until you’ve had the pleasure of reading the story itself.

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The Grasshopper

Since John Harrison was a cabinet-maker, he knew all about constructing things from wood. In fact, the first clocks he built as a young man had all-wood mechanisms. When designing a ship’s clock, he replaced many metal parts with wooden ones. Harrison used an oily wood named Lignum Vitae which didn’t need to be lubricated. Then, he designed a brand-new kind of escapement: the Grasshopper. The Grasshopper escapement worked with way less contact with the clock’s gears, which meant less lubrication was needed.




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A dumbbell idea

The problem with clocks in the 1700s: the ship’s rocking messed up a clock’s pendulum movement; the salty sea air corroded the metal gears; changes in temperature and humidity made metal clock parts expand & contract. All these things made a clock inaccurate—it was too slow or too fast.

Harrison came up with some innovative ideas to counter-act these problems. The first one was a dumbbell-style of pendulum. Instead of a rod with a weight at the bottom swinging from an axis, Harrison put the axis in the middle of 2 rods with weights at top and bottom—then he connected them with springs so they would keep moving back and forth no matter how the ship bounced around.

Standard-issue pendulum at the left; Harrison’s dumbbell movement at the right.

Start at 1:00—

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Like a pendulum do

One time while sitting in church, Galileo noticed a lamp suspended from the ceiling that was swinging back and forth. That motion is known as a pendulum. As it swung, he observed the lamp kept the same rate of speed. It occurred to Galileo that you could use a pendulum’s regular rate of speed to regulate a clock.

We learned that in Galileo’s time a clock was powered by a weight that slowly released its energy as it was pulled to Earth by gravity. The mechanism that slowed down—regulated—the weight’s energy is called an escapement. Galileo thought to replace the verge and foliot escapement with a pendulum escapement.

Just like the verge and foliot, as the pendulum swings back and forth it allows a gear to move forward a little bit just before a pawl stops it—until the pendulum swings to the other side. The pendulum escapement releases-stops-releases-stops the gears as they move the hands of the clock. Here is an excellent animation of Galileo’s escapement. Notice how when the gear turns it gives the pendulum a teensy little push.

https://www.history.com/topics/inventions/galileo-galilei
http://www.cs.rhul.ac.uk/~adrian/timekeeping/galileo/

Watch this guy make a wooden pendulum clock: https://www.youtube.com/watch?v=rvU37Aho4FA

Here’s some terrible music:

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