6. The back taper T is made for the same reason. Some watchmakers (?) seem to think this is added only for ornament, but it is a very important factor in producing longevity of the oil.
7. The slight chamfer C, in the bearing, serves two purposes; it becomes a reservoir for oil and removes any burr that might otherwise exist in a metal bearing, without in any way altering its effectiveness.
8. It will thus be seen that the oil reservoirs O, O´ and C are made to contain, and retain, the maximum amount of oil, and the supply of the lubricant is thus increased to a maximum length of time.
The application of these principles to each part to which they relate will be considered.
48. The Barrel Arbor, with its bearing, should be so constructed that the oil will not spread to the contiguous parts. The oil sink, with circular groove cut around the outside (46-47), both in the barrel and its cover, should not be neglected.
It is well to apply oil to the bottom and on the cover of the barrel, as well as on the coils of the spring; and before putting on the cover, a small amount applied on the arbor nut at the shoulders will assist greatly in causing the oil to be at once drawn to its proper place.
Care must be exercised while and after cleaning the mainspring, in order that it may come in contact with the fingers as little as possible, as the acids contained in perspiration are liable to be transferred to the spring and so work serious injury by contaminating the oil.
A part frequently neglected is the point of contact of the click spring with the click. If this part be not oiled rust is likely to form, and many instances have occurred where rust has found its way all through the movement from this cause. In fact, this may be said of the point of contact of all springs, with few exceptions, both in plain and complicated work.
If the watch has a chain and fusee, these both should be looked after; the former can be well oiled, and the surplus wiped off so as to leave a minute quantity in the interstices of the links; while the latter should have oil on its clicks, as well as on the arbor where it passes through the wheel. If the ratchet of the maintaining power be of brass it should not be oiled; while if it is of steel oil should be applied. Its click should have the pivots of its arbor oiled, while what was said of clicks in general will apply here.
49. The Center Pinion Pivots, with their bearings, should be very carefully constructed, as this is the vulnerable point of most watches. With proper precautions (46-47) these parts can be made so as to wear as long as the rest of the watch.