One of the things that makes flip clocks so interesting, is the fact that while they are digital clocks, and were considered quite "modern" in their day, they are purely mechanical, or more precisely, electromechanical. The mechanical design won awards back in the day (late 60s to 70s) and the minute by minute flipping of numbers was found to be mesmerizing by many. Today, flip clocks bring back memories of the "space age" for those who lived it, and today are sought out for those interested in retro home decor.

This article will discuss the basic workings of the fip clock. Following this will be a movie of the examination of a flip clock mechanism.

The clocks use what's known as a split flap mechanism. The "pages" or tiles containing the numbers are attached to what could be called a wheel (sort of like a ferris wheel) and appear like an open book. There is one wheel for the hours and one for the minutes. In this case, the book is held vertically with half of the number on each page. The pages are held back by a usually sliver colored metal tab, which gradually releases each number as the motor turns the wheels.

The working of the clock is dependent upon the power grid, that is, the electrical supply. In the United States, the electrical current alternates at 60 times a second, known as 60 Hertz or 60 Hz. In other countries, the electricity is 50 Hz. In any event, the electrical current causes the motor of the clock to spin at a certain speed. Knowing this rate of rotation (based on the frequency), allowed the designers of the flip mechanism to gear the movement in a way that allowed the hour wheel, holding the "pages" of numbers to turn at a rate of once per 24 hours while the minute wheel, holding the numbers from 00 to 59, turns at a rate of once per 24 hours.

Note that the releasing of the pages is not particularly exact. This presents a problem, since a simple metal tab, over time as the tab or the numbers begin to wear, may release the numbers at slightly different rates. Not too much of a problem, except when the hour changed. Getting the hour to drop exactly as the minutes moved from 59 to 00 in this situation, would be basically impossible without something extra. That's where the fun begins.

Located between the wheels of numbers, you'll find a flat metal spring. As the minutes move closer to 59, a thickening of the minute wheel, usually around 37-40 minutes, pushes this piece of metal towards the hour wheel. The flat spring has an extension positioned so that the hour page will be held back once it's released from the silver metal tab previously discussed. The outgoing hour drops to the metal flat spring and is held there by the thickening of the minute wheel. When 59 minutes rolls around, the thickening of the wheel drops off completely. To continue to hold the metal spring over to keep the hour page from dropping too soon, the 59 page has an extra tab keeping the spring in place. When the 59 page finally drops, the spring holding the outgoing hour page moves back towards the minute wheel, dropping the hour page exactly as the minute changes to 00.

Go ahead, take your own flip clock for a spin.