Three Wheel Skeleton Clock

A clock is generally any mechanism for time keeping other than a watch or chronometer.

Mechanical clocks have a series of wheels (gears) called a gear train.  The train is driven by either a weight or spring.  Time only clocks have one gear train.  Clocks with strike or chimes mechanisms will have additional gear trains driven by their own weight or spring.  Most mechanical clocks have five wheels and pinions in the train.

Principle Components of a Clock:

Weight or Spring - drives the movement or rotation of the train

Escapement - controls the movement.  It has two parts: an Escape wheel (the wheel that permits the escapement or rotation of the train) and the Palates (the surface or part through which the escape wheel gives impulse to the pendulum).

Pendulum - regulates the movement

This gear train has two 480 tooth wheels, two pinions, one with 10 teeth and the other with 8, and a 60 tooth escape wheel. Each wheel engages a pinion. In clock terminology, the larger of two gears in mesh is always referred to as the wheel and the smaller gear as the pinion.

Great Wheel and Center Wheel

While the great wheel and the center wheel each have 480 teeth, the center (second) wheel is slightly smaller than the great (first) wheel.  This is to allow for clearance between the center wheel and the great wheel arbor.

Escape Wheel and Pinions

The escape wheel is made from .030" thick titanium and was cut on a wire EDM.

Great Wheel and Spring

The gear train is driven by a 3/4" x .017" x 120" spring attached to the great wheel allowing the clock to run for one month between windings.  The great wheel makes one revolution every 48 hours.

Center Wheel with Pinion

The center wheel is driven by the 10 tooth pinion attached to the center wheel arbor.  The 10 tooth pinion meshes with the 480 tooth great wheel.  Thus, with the great wheel making one revolution per 48 hours, the center wheel makes one revolution per hour.

(480 divided by 10 = 48)

Escape Wheel with Pinion

The escape wheel is driven by the 8 tooth pinion attached to the escape wheel arbor.  The 8 tooth pinion meshes with the 480 tooth center wheel. Thus, with the center wheel making one revolution per hour, the escape wheel makes one revolution per minute.

(480 divided by 8 = 60)

Escapement - Escape wheel and Pallets

This clock has a dead beat escapement, (an escapement in which the escape wheel does not recoil), designed for a 9" pendulum.

The pallets rock back and forth controlled by the pendulum allowing the escape wheel to advance one tooth at a time. 

Beat Adjustment 

While the pendulum controls the rocking of the pallets, the beat adjustment allows for some rotational adjustment so that the pallets fall equally on the teeth of the escape wheel.  This adjustment is termed putting the clock "in beat".

The time it takes the pendulum to swing (the period) is adjustable by changing the length of the pendulum, i.e., moving the weight closer to, or farther away from, the pivot point.

Motion Works with Hands

Since the center wheel makes one revolution per hour, the minute hand is attached directly to the center wheel arbor.  The motion works are a set of 4 gears that slow the rotation of the hour hand to 1/12 of the speed of the minute hand. In the photo above, a 10 tooth pinion attached to the center wheel arbor drives a 30 tooth wheel.  An 8 tooth pinion attached to the 30 tooth wheel drives a 32 tooth wheel.  The hour hand is connected to the 32 tooth wheel.  

(10 divided by 30 = 1/3, 8 divided by 32 = 1/4, 1/3 times 1/4 = 1/12)