Friction, Lubrication and the Lubricants in Horology

by W. T. Lewis

The conical pivot shown is the usual form in the finer grades of American watches; and as this form of pivot combines strength with a minimum tendency to attract the oil from the jewel hole, it is to be highly recommended. The back-taper T should never be neglected for reasons previously (47, 6) given. The proportions that should exist between the diameter of the pivot and the length of its bearing surface, as well as the shape of the end of the pivot, cannot be discussed here, as the scope of this work will not permit; but it should be borne in mind that the smaller the pivots, consistent with strength, the less the fluid friction will be. The sides of the pivots should be straight and parallel for a minute distance from their bearing surfaces; while the form of the rest of the pivot should be a gradually increasing curve, terminating at the point where the back-taper begins.

The proper proportion of the diameter of the pivot to the diameter of the jewel hole varies according to conditions; but it has been previously (37) shown in a general way what this should be.

55. The Escapements should be constructed in such a way that a maximum durability of oil may be secured. The acting surfaces of the teeth of the scape wheels should be made as small as possible consistent with durability (43, 8); while enough metal should be left near the acting surfaces to be sufficient to retain the oil and prevent its attraction to the web of the wheel. The teeth of chronometer scape wheels should not be oiled, as it is liable to seriously alter the rate. When the oil becomes viscous by oxidation or by cold it would produce too much variation of fluid friction and so diminish the effort (25) of the mechanism. Some watchmakers oil the fork of the lever in anchor escapements very slightly, by applying oil and then using pith to remove any surplus, while others never oil the fork. The writer has frequently observed ferric oxide or "rust" on the roller, fork, and on the plate or potance; but whether this was the result of not oiling or of oil having been applied which afterward become gummed, or evaporated, it would be interesting to know.

56. The Curb Pins sometimes produce the ferric oxide mentioned by their action on the hairspring. This has been remedied by the same method as used in the fork just referred to, and if a very minute quantity of oil can be applied—such a minute quantity that if the whole spring were equally covered by a coating of oil equally thin, such film being so thin that it would have no tendency to cause the coils to adhere, or to cause small particles of matter to adhere—then it may be that this method deserves notice.

By making a solution of benzine and oil (100 drops of the former with 1 to 10 drops of the latter) and by immersing the hairspring in this solution and on withdrawing it dry it quickly between soft, fine linen, it will be found that the coils of the hairspring do not adhere to each other. The effect that this would produce on the whole spring by way of preventing rust in damp, warm climates, will be stated (78) later.

57. The Application Of Oil must be attended with great care. The shoulders of the barrel and center arbors may be profitably oiled before putting them in their places, applying an additional small amount afterward. The rest of the pivots should be oiled after the movement is set up—except in the case of capped jewels—as if oil is applied to each pivot as the wheel is put in position it would be difficult to keep the oil in good condition and at its proper place if it should be necessary to take the movement apart again for any purpose.

The oil is more evenly distributed on the teeth of scape wheels, where such require lubrication, if a small quantity of oil be applied to each tooth, or every second or third tooth. A small amount added to the surfaces on which the teeth act will in most cases be beneficial. If it be necessary to take the movement partially apart for any purpose, after it has been oiled, care should be taken not to give the train a too rapid motion, as the centrifugal force (23) resulting from the rapid circular motion of the wheels will be liable to cause the oil to leave the jewel holes and spread upon the surfaces of the jewels, and also cause the oil to fly off the teeth of the scape wheel to its determent and that of other parts which are better without oil.

58. The Method of Oiling Capped Jewels has been given by Saunier, as follows:[11] "When a drop of oil is introduced into the oil cup of the balance pivot-hole, insert a very fine pegwood point, so as to cause the descent of the oil. When this precaution is not taken, it frequently happens that in inserting the balance pivot its conical shoulder draws away some of the oil, and there is a deficiency both in the hole and on the endstone." In both the English and American editions, this erroneous method is repeated.

By this means, only an insufficient quantity of oil can be caused to flow into the reservoir, as the pressure of the air inside will prevent the oil flowing in; as, in the case of a glass tube with the upper end sealed up, it has been shown (22, 2) that the water refused to be drawn up the tube, even with the added pressure caused by the lower end of the tube being below the water line. Again, the point of pegwood is liable to have minute fibres of wood adhering to it, which will be incorporated with the oil; and its liability to break off, and remain in the jewel hole, is another reason why pegwood should never be used. The author advances a method, which is not open to these objections, as follows: When about to place the cap jewel in position—after the hole jewel is in place if it be in a setting—a small quantity of oil is placed ON THE CAP JEWEL, as shown at O, Fig. 14, being very careful to allow no oil to spread upon the cap jewel setting. This setting is then carefully placed in position; when the oil, if the operation has been skillfully performed, is seen to be collected in the reservoir R and in the jewel hole. The appearance which it will assume is shown in Fig. 14. The advantages which this method possesses are: the reservoir can by this means be made to contain the maximum quantity of oil; and the oil cup or sink S is left with its surface dry, thereby exposing less oil to the influences of the air; and, at the same time the tendency of the oil to flow towards the shoulder of the pivot is decreased.

Skill is necessary in order to judge of and place the requisite amount of oil on the cap jewel before putting it in position; as, if too much is used it is worse than if too little is employed, because the oil would then flow on to the setting, and from there between the settings at b, when it will rapidly be all drawn from the bearing, leaving it dry, while the settings are copiously supplied. The approximate relative position which the oil should occupy is shown at d, Fig. 14, in section; and this can be seen by looking through the jewels with a double eye-glass, when a true circle, concentric with the jewel hole, will be seen to have formed. This circle represents the limit of the distance which the oil has flowed from the jewel hole. When too much oil has been applied, this limit is not a circle, but represents a U.