Components › Movement › Display & motion work

THE CANNON PINION

MENU

1. General description

The pivot of the centre pinion passes through the main plate and emerges, generally at the centre of the movement, on the dialof the latter. The cannon pinion is a cylindrical tube, generally blind when there is no central seconds hand, at the base of which a toothing is cut in a larger diameter. The cannon pinion fits onto the pivot of the centre pinion, previously greased. So that the cannon pinion can be driven by the centre pinion, a groove (nick) is made on the pivot of the centre pinion. The tube of the cannon pinion is then pinched at the same height as the nick of the centre pinion’s pivot. This pinching creates sufficient tightness for the cannon pinion to be driven by the centre pinion. It also offers the advantage of being light enough to let the cannon pinion turn freely on the centre pinion when setting the time on the watch (friction fit). This friction is called indenting. A good indenting is considered sufficiently tight when the movement can be stopped when setting the time counter-clockwise.

Once driven by the centre pinion, the cannon pinion turns at the same speed as it (1 rev/h) and can thus directly carry the minute hand, which is pressed onto a seat located at the top of the cannon pinion. The toothing of the cannon pinion drives the minute wheel whose pinion can drive the Hour wheel (pipe wheel) (reduction train) superimposed on the Cannon pinion.

Figure 1

Diagram of an indented Cannon pinion

Click on the thumbnail to enlarge it

Figure 3

Diagram of the link between the Cannon pinion and the Motion work

Click on the thumbnail to enlarge it

2. Artisanal manufacturing of a Cannon pinion

The Cannon pinion is a relatively simple element to produce, whatever the method. It is a cylindrical pinion made of Steel devoid of pivots. All the operations required for its manufacture can be carried out using a Lathe and a dividing head (turning, gear cutting). To minimize friction (particularly the contact surfaces with the Hour wheel), the Cannon pinion is entirely polished. This is also a step that can be carried out on a conventional Lathe.

Finally, and in most cases, the craftsman will carry out any Heat treatments required by the chosen steel Alloy (hardening, tempering, annealing). He will then re-whiten all the surfaces of the Cannon pinion that were colored by the successive Heat treatments.

3. Industrial production of a Cannon pinion

On an industrial scale, the cannon pinion can be entirely manufactured by an automatic lathe. Its manufacturing is simple, involving only a few turning operations and the cutting of the teeth. To minimize friction (particularly the contact surfaces with the hour wheel), the cannon pinion is fully polished. Depending on the alloy chosen for its manufacture, the cannon pinion will then undergo the heat treatments needed to achieve optimal hardness.