By Emanuel Eeibel
They spend a great deal of time on the escapement and balance and think if they have these as near perfect as is possible, they have done their duty and they are not so careful as to what mainspring they use for that particular watch. Just any spring will do, just so they get a motion though it does not give them as much as might be expected, or it should.
The very act of replacement of a mainspring may be the cause of wrong performance. Unless the spring is replaced by a winder, the spring may become so distorted that you have set up frictions in the barrel.
The improper width and strength may cause serious trouble in an even delivery of power. And an even, steady delivery of power by the mainspring is a prime requisite of good timing and isochronism.
Every different size of mainspring barrel requires a different mainspring.
As we know, watches today are made to run 36 to 40 hours at one winding, the mainspring must be of the proper strength to accomplish this; if we put in too strong a spring it cuts down the running time of your watch; if too weak, it will have a longer running time but not enough motion. WHY?
There is a law established by experience which says that the space, actual area, that the mainspring occupies when run down must be the same as when wound up tight around the barrel arbor. Also, that the difference between the number of coils when down and when up, is the number of turns the barrel will make in running the mainspring down. Therefore, it is self-evident that too strong mainspring cuts down the running time of a watch because the difference of coils up and down is less and just the opposite when the spring is too weak. Then, again, you may have the correct strength but not the correct length.
Sometimes we may be forced to use a spring stronger than originally called for, due to wear of parts, but we can compromise by using a somewhat shorter spring and still keep the running time of the movement what it should be.
Mainsprings were the first thing that made the pocket watch possible, but it did not bring this to pass at once. It brought the portable timepiece, table clock. into existence and then Peter Henlein of Nuremberg, Germany, produced the watch popularly known as the Nuremberg Egg, . which was a large cumbersome affair as watches go today. This happened about 1500 A.D.
The first mainsprings were not enclosed in a barrel, but soon this came about as a safety measure, for in case of breakage the spring was confined and the train received more and better protection.
At first the mainsprings were a crude affair and they went through a lengthy evolution until we come to the present-day product. They were made of a tapered thickness; they had an attachment called the stackfreed attached to the barrel arbor.
To attempt an equalization of the power delivery: We had and still have on some high grade movements a device called a stopworks, whose object was to utilize the central portion of the mainspring. In this manner we get away from the excessive strength of a tightly wound mainspring and the weak pull of the last tag end of the unwound mainspring.
Another device which was used commonly in a great many ordinary watches and is still used in ships chronometers-is the Fusee, which consists of a cone-shaped device with a track cut into its surface to furnish a seat for a chain which winds around it in winding, and unwinds when running down. This device winds the chain from the large diameter up its surface until it is wound on a very small diameter, from around the mainspring barrel. When this is wound up, the chain pulls on the small diameter of the Fusee and as the spring unwinds, it pulls on a continually increasing diameter of the Fusee, thus endeavoring to equalize its power.
Today in all pocket watches this has been discontinued due to the refinement of the present-day mainspring and they depend on the first 2/3rds of the running time of the mainspring, and it seems to answer the purpose very satisfactorily, for we find if we wind our watches regularly on a 24 hour schedule, we keep its rate even, day in and day out.
This we can check for our own satisfaction by taking a high grade watch which has been rated very closely and wind it religiously at exactly the same time for a week or two and it will stick to its rate. Then begin to wind it irregularly, say anywhere from 20 to 28 hours for a week and carefully check your watch from day to day and see what happens. You will get a variable rate, not an excessive rate necessarily, but still a variable rate depending upon whether we wind it too soon or too late.
I forgot to mention another thing and that is 'to check on every mainspring with T end or double brace and· make absolutely sure the ends which extend through openings in barrel are not too long for there is always the possibility of the protruding ends catching and stopping the watch, and unless carefully checked, it may be troublesome to find cause of stoppage.