# Clock Gear Train & Hand Speeds

How one unwinding spring drives a clock's gear train, so the second, minute and hour hands turn at three different speeds\.

By gentle\-otter\-8c981f29

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/10cCZmjC6y2F)

## Transcript

### 1. One spring, three speeds

Behind a clock face hides a chain of gears called a gear train\. One spring drives it, yet the second, minute and hour hands all turn at different speeds\. Let's find out how\.

Drag empty space to turn the clock and look behind it\.

### 2. The power: a coiled spring

A mainspring is coiled up inside this toothed drum, called the barrel\. As the spring slowly unwinds, the barrel turns about once every 12 hours in this clock\. Its big ring of teeth pushes the whole train\.

Shown 240 times faster than real time\.

### 3. The minute hand's wheel

The barrel's 96 teeth push a tiny pinion, a small gear with just 8 teeth called leaves\. That makes the centre wheel turn 12 times faster: exactly once an hour\. Its axle, the arbor, carries the minute hand\.

Shown 60 times faster than real time\.

### 4. Big wheel, little pinion: faster

Each big wheel turns the small pinion of the next one, so every wheel spins faster than the last\. 80 teeth on 10 leaves gives 8 times faster, then 75 on 10 gives 7\.5 times\. 8 times 7\.5 is 60, so the fourth wheel turns once a minute and carries the second hand\.

Shown 10 times faster\. Neighbouring wheels turn opposite ways\.

### 5. The escapement keeps the beat

Left alone, the spring would whizz the gears round in a blur\. The escape wheel and pallet fork let the train move one tooth at a time, timed by the swinging balance wheel\. Every release is a tick: five each second here\.

That is 18,000 ticks an hour, a common beat for mechanical watches\.

### 6. From minutes to hours

The hour hand gets its own little gear set, the motion work\. The cannon pinion's 12 leaves turn the 36\-tooth minute wheel 3 times slower, and its 10\-leaf pinion turns the 40\-tooth hour wheel 4 times slower\. 3 times 4 is 12, so the hour hand goes round once in 12 hours\.

Shown 120 times faster\. The hour wheel's tube fits over the minute hand's tube, so both hands share one centre\.

### 7. Race through one hour

Press the button to run one hour of clock time in 12 seconds\. Watch the counters: the second hand goes round 60 times, the minute hand once, and the hour hand only one twelfth of the way\.

### 8. One train, locked together

In 12 hours the second hand turns 720 times, the minute hand 12 times and the hour hand once\. Teeth lock all three together, so they can never drift apart\. Try the speeds to watch the whole train at work\.

Setting the time? The cannon pinion slips on its arbor, so the hands turn without forcing the train\.