Friction, Lubrication and the Lubricants in Horology

by W. T. Lewis

In a high-priced watch the bearings should be jewels; but in a cheap watch, where the price will not warrant correct work and careful fitting, the bearings are preferably of brass or some other metal.

Where the bearings of the center pinions are of brass or nickel, there is little difficulty experienced in making them perfectly "upright"—a condition necessary to produce a minimum amount of friction—while, if the bearings are jewels which are not upright, the friction, and consequent wear, will be increased. Properly jeweled bearings produce a maximum durability, as they cause the least friction; while the coefficient of friction is subject to much less fluctuation on account of the harder, smoother surface of the jewel, (43, 46, 47 and 61).

Where there is a brass bearing for the lower pivot, in watches having a solid center arbor on which the cannon pinion revolves in setting, the length of the bearing may be profitably increased by making a boss on the outer side of the lower plate, provision for which is then made in the cannon pinion by a suitable recess. In either case the laws previously given should be complied with.

A source of mischief in many watches is the manner in which the minute wheel is made; the construction being such that its teeth touch the plate so near the bearing of the center arbor that capillary attraction (19, 22) is produced, which causes all the oil to leave the lower bearing of the center arbor. This can be avoided by cutting off the lower parts of the teeth of the minute wheel; or, by turning a groove in the plate which will be concentric with the minute wheel post, and which will pass under the teeth of the wheel, but not near enough to the bearing of the center arbor to injure the latter.

The oil from the stem wind mechanism, also, sometimes flows under the minute wheel, and from there into the center arbor bearing; and, when the oil is used up in the former place, it is drawn up again out of the latter place leaving it dry. A means of preventing this will be discussed (59) later.

Another and very frequent cause of the lower center pivot cutting, particularly in new watches, is the neglect to remove the polishing material from the cannon pinion where the center arbor is solid.

A small portion of oil should be applied to the bearings of the minute wheel, (where its pinion, or the pivot on which it revolves, is steel), hour wheel, and cannon pinion where the center arbor is solid, and to the set hands arbor where the center arbor is hollow. The safety pinion should always be oiled, as it may not otherwise be of much service.

50. The Third Pinion Pivots are sometimes the source of mischief. When the center wheel is placed above or below the barrel, the upper or lower pivot of the third pinion receives such great stress that the oil is forced out in many cases. By increasing the length of the pivot this could be obviated. The minute wheel is sometimes so close to the lower bearing of this pinion as to absorb the oil. This can be remedied by cutting a recess in the lower side of the minute wheel. Where it is possible to do so the wheels should be so placed on their pinions and arbors, and at such a distance from the bearing surfaces of the latter, that the stress on each pivot—the combined result of the weight of the wheel and the forces acting on it—will be equal.

51. The Fourth Pinion Pivots should follow the same general laws as that given for the rest of the train; but it should be borne in mind that fluid friction acts as a retarding force much more perceptibly in the lighter parts of the train; consequently if no second-hand is to be carried, very small bearing surfaces should be the rule in this case.

52. The 'Scape Pinion Pivots as well as the shoulders should not be too large, while there should be sufficient back taper to insure the oil remaining at the pivots. A very small quantity of oil should be applied, as, when too much is used, it is liable to work up into the pinion where the latter is short, as in very thin watches, thus producing, when very fine dust is added, a mixture that acts much like oil stone power and oil, which cuts away the leaves of the pinion.