Wheel. In horology → in general, a metal ring with teeth on its circumference. Horologists use various kinds of wheels , but the most frequently used in watches and clocks consist of a ring, c ( see figures and plates ), arms b ( see Barrette), a center or small circle l [1], and finally an arbor or pinion on which the wheel, set on a hub, turns perfectly straight and round; the whole is always called wheel , like contrate wheel , crown wheel , etc., indicating the wheel and the pinion mounted on the arbor with it.

Names of wheels making up various clocks.

Wheels in the movement of a watch [2]. The first is the great wheel , carried on the fusee arbor. See Watch, Fusee, and the illustrations. In this figure, part K is a prominence called a collet; it lengthens the hole for the wheel or its pipe and strengthens this part so that on the other side a sink may be made for a steel collet, whose function will be shown in the article Fusee. The dark portion, o , is a sink extending to the edge, c ; in it are lodged the ratchet and pawl, and the fusee ratchet rests on the bottom.

The second wheel of a plain watch is the great middle wheel , see the plates and figures; in clocks it is called the long-arbor wheel , having a shaft, t , towards the pillar plate that carries cannon e . Since, as the caliber is planned, this wheel is usually at the center of the dial, the number of wheels is always arranged so that it makes a revolution in 60 minutes; for that reason the minute hand is mounted on the cannon. See Cannon, Movement, Caliber, Watch, etc.

The third is the small center wheel , see following plates . It is flat and similar to the preceding one but a bit smaller; it is mounted by means of a hub on its arbor with a pinion of six or seven leaves. See Hub. This wheel meshes with the pinion of the crown wheel .

The crown wheel , see figures, is the first one seen when a watch is opened. Its teeth are parallel to the arbor, not perpendicular, and stand perpendicular to the plane of the ring and the arms. This form is required for this wheel so that it may mesh with the pinion of the contrate wheel , whose arbor is perpendicular to the balance staff and parallel to the plates.

Contrate wheel . The teeth of this wheel , the last one in the plain movement, are always uneven in number. They are like slanting points, placed parallel to the arbor like those of the crown wheel . They engage the pallets, as explained in the article Escapement. See ← Horology → plates and explanations. The pivot of the contrate wheel nearer the wheel turns in a hole drilled in the end of the potence, and the other in the insert of the lower potence. Sometimes the two latter wheels are made by stamping, in order to make their surfaces harder. See [Plate V,] Figure 27.

Motion work wheels . Two flat wheels , namely the hour wheel with 40 teeth and the minute wheel with 36. The first is staked to a pipe that fits freely but without excessive play on the cannon pinion. This wheel is held with suitable clearance between the dial and the pillar plate; it carries the hour hand on the tip of its pipe extending through the dial.

The minute wheel, also called the intermediate wheel , is driven by the cannon pinion, which has twelve leaves; it has a pinion of ten, called the intermediate pinion , which drives the hour wheel. It has a center hole and revolves with its wheel on a stud fixed perpendicular to the pillar plate under the dial, as shown in the figures.

The worm gear wheel, see plates and figures  [3] , meshes with the worm gear and is mounted on the squared end of the barrel arbor; by means of the worm gear, the spring tension is adjusted.

The regulating wheel, following figures , meshes with the rack and is used to make the watch go faster or slower.

Repetition wheels . In a repeater the time train is distinguished from the strike train; the wheels of the former and the motion work are similar to those of a plain watch. As to the strike wheels , they are five in number, if one excepts the first, called the strike great wheel , which has a ratchet and click and is quite similar to the great wheel of the time train. They are flat wheels paired with six-leaf pinions; they diminish in size till the last one, which meshes with the governor. See Strike, which explains the function of these wheels .

Wheels in clock movements. Spring-driven clocks usually have five, distinguished in the following manner (following ← Horology plates) [4]: 1) barrel R, 2) second wheel S, 3) long-arbor wheel T, 4) crown wheel V, and finally the contrate wheel X [sometimes also called crown wheel ]. The last two differ from the same ones in a watch only by their size. We have just seen the long arbor wheel , which corresponds to the middle great wheel ; as for the barrel, it is a conventional barrel with teeth around the circumference. In seconds clocks, where the verge or contrate wheel escapement is almost never used any more, the last or escape wheel is also called the ratchet , and the crown wheel , which thereby becomes an ordinary wheel , is then called the third wheel because these clocks have only four, and the first is called the great wheel . See Ratchet. In general, in all kinds of clocks, etc., the first wheel of the movement is called the great wheel , and the last one the ratchet or contrate wheel according to its shape, flat or crowned. It is nearly the same in watches, although usually the last wheel retains the name of contrate wheel , although it is not made in the same way as those commonly so named.

Strike wheels. Their number is not absolutely fixed but varies according to the striking; in clocks it is usually five [5]: the barrel W, the second wheel P, the pin wheel O, the stop wheel M, and the fan wheel N; there is no more fan E. We have said that in all clocks there is a great wheel and a contrate wheel or its equivalent; likewise in all strike trains there is a great wheel , a pin wheel , and a stop wheel . In tall clocks, the great wheel is also the pin wheel . This wheel is so named because it carries pins that lift the hammer tails or levers. The stop wheel takes its name from the stop pin on its circumference that stops the strike train; when the strike is at rest, this pin rests on the detent. This wheel usually makes one revolution for each stroke of the hammer. See Strike. In several strike trains, it makes only a half-revolution; then it is fitted near its circumference with a ring cut into two halves; after the hour has struck, the detent drops into the notches between the two portions of the ring. This method of stopping the strike is more reliable than a pin stop for poorly-made clocks, as we have said. See Strike, Clock, Pendulum, etc. There is also the count wheel , which is the same as the count plate. See Count plate.

Notes:

1. References to a plate that is lacking (translator's note).

2. The following references do not agree with Plate X ff ., "Watch" (translator's note).

3. No plate shows the wheel; the worm is shown in Plate X key BB, Figure 4 (translator's note).

4. The repeating clock is shown in Plate VI, Figure 28, and the repeating watch in Plate X, key EE. The references in this description do not agree with those illustrations (translator's note).

5. Here again, the references do not agree with the illustration (translator's note).