c4.4.4 The Pillar Wheel

The chronograph needs to be operated by the user of the timepiece. 

There are several functions common to most chronograph mechanisms…

1. A chronograph will need to be engaged.

2. It will need to be disengaged.

3. It will need to be reset.

In order to engage the chronograph there will typically be a pusher installed into the watch case. When the pusher is depressed it will act upon a lever called an Operating Lever.

For this lesson we shall discuss the pillar wheel based chronograph, and later we shall discuss the differences with cam based chronograph movements.

The operating lever is manipulated by an extended portion of the case pusher when it is depressed. The operating lever will usually be secured with a shouldered screw allowing for free movement so that it can pivot. With a cam based chronograph, the lever will have a pawl fitted which is held under tension with a spring. 

When the lever pivots, the pawl will pull on one of the pillar wheel teeth and cause the pillar wheel to turn by the distance of one of those teeth. The pillar wheel will also have a spring which bears down between one tooth and it’s neighbour in order to stabilise it’s position.

Lets simulate a press of the pusher – I will press one end of the operating lever where the pusher would normally engage it. Due to the levers pivot point, it will cause it’s pawl to pull on one of the pillar wheel teeth. Please observe the spring here gaining tension as the pawl is pulled back.

When I release the lever this spring causes the pawl to slide back to the next tooth on the pillar wheel.

The movement of the pillar wheel will cause several further chronograph components to shift their positions, such as…

– The Coupling Clutch

– The Sliding Gear

– The Return Hammer

– Blocking Lever