By Rev. Francis Bimanski
A century ago the famous philosopher, Balmes, mentioned a rather simple way of improving our knowledge and wisdom. "Before reading a book or even a chapter," he says, "just sit down, gather your thoughts and test your knowledge on the subject, reviewing your past studies and experiences. Then only begin your lecture, correcting and enlarging your views and storing new treasures in your memory." This method is surely full of common sense. The philosopher possessed a deep insight of human nature. He knew how little we profit from all the long years of study. It would be well, just for relaxation, to try the method and test, for instance, our present knowledge of a subject of some importance, I mean the mainspring.
A spring, in general, requires a material that yields to a force and at the same time resists. This resistance is used as a new power. In due proportions, the resisting force is equal to the force applied. In great mechanics an axiom says, "The width of the spring increases the resistance power proportionately the thickness cubes it." The reason for the last is obvious. The thicker the band, the greater is the exterior expansion and the interior compression. But, the axioms of great mechanics do not seem always to fit fully in the smaller mechanics of horology, according to the observations of some learned professors. The reason is that tests from which general laws were deduced and formulated were limited in their character and numbers.
Elasticity implies a resistance to force and the faculty of returning to the original form. It has it limits, a spring may be overtaxed and deform or break. The study of 15 used mainsprings shows a difference of .01 and .02mm between the center and two ends.
Mainsprings in watches:
A mainspring is a band of steel embedded in a barrel. Its duty is to furnish power to the watch. The process of making a first class spring is not so simple as we might expect. There are numerous operations, the choosing of the right material, the hot and cold rolling into bars and strips, the frequent annealing, the cutting into strips, the testing for hardness and flexibility and the equalizing of the tension while reversing the coils. Yet, each factory seems to keep its own secret, they say.
In late years much experimenting has been done. Different alloys have been and are at present proposed. Beryllium bronze is gaining in favor. The experiments with steel inaugurated by the auto factories will sooner or later produce an alloy that will satisfy the demands of the profession. Meanwhile, which ones are the best only time will tell.
The spring must have the right dimensions in width, length, and thickness. Width is determined by the barrel, about .lmm is granted for freedom of action. The latest experiences seem to favor wide springs.
Length is limited by the size of the barrel. The spring must be long enough to furnish steady power for 36 hours. It cannot be too short, nor too long, although an excess of one centimeter in a 16 size watch would not exercise a great influence, according to a Swiss professor.
The rule is, the empty area must be equal to the area taken by the spring, or the area for winding and unwinding must be equal. The object is to obtain the maximum capacity of the spring. It is clear that the unwound coils are less numerous than the wound ones, and that the difference gives the number of active coils. Some find it difficult to divide the area reserved for the spring into equal areas. The theoretical problem belongs to geometry, the practice is easy. In the area reserved for the spring draw a circle and a line perpendicular to a radius passing through the center of the barrel. The two points at the periphery will give two points for the circle dividing the area into two parts.