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Make Your Own Working Paper Clock - by James Smith Rudolph

Book Review, © Copyright 2001, Jim Loy

That's right, a paper clock. It is a pendulum clock, run by a slowly falling weight. Cut the pieces right out of the book. It contains adjustable paper pendulum, gears, escapement, and supporting structure, over 120 pieces in all. Supply your own wire for axles etc., and string, and sand (or whatever) for inside the weight. The finished clock even makes a "tick-tock" sound. Preface by Isaac Asimov, who recommends that you buy three or four copies, as your fourth clock will be better than the third. This book is a lot of fun.

There is a typo in the book. If you want to use beads as bearings (to reduce friction and improve the accuracy of the clock), the text mislabels the places where you want to glue the beads. It gives + for places to glue the beads and + to not glue the beads. One of those should be a + with four dots. I observe that real clocks have jewels as bearings on non-moving parts, and the axels turn within those motionless jewels. It can probably be done the other way, but positioning the beads sloppily may upset the balance of the wheel.

To order this of book, click on Amazon.com (goes directly to this book).

Theory:

How does a pendulum clock work? On the left we see my drawing of an escapement (the book's escapement looks better than this). The toothed wheel is powered by the falling weight. The escapement is the little gizmo at the top, which rocks back and forth. It is loosely attached to the pendulum, and takes a second or so to rock back and forth. One complete rock (back and forth) lets my toothed wheel rotate one eighth of a turn. The toothed wheel and escapement also give a small boost to the pendulum, to keep it from running down. The rest of the clock mechanism is made up of gears, to turn the hands at the desired rate. The pendulum is the only thing that influences the rate at which the clock runs. Friction and the size of the weight have little influence. In a mechanical watch, the escapement is attached to a little spring that rocks back and forth.

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