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Cylinder Escapement

This escapement is one of what is known as frictional escapements, and the credit of the invention is given to George Graham. In the earliest watches to which it was applied the escape wheel was made of brass, but in this form it was unsatisfactory on account of the wearing caused by using a brass escape wheel. In later years a hardened steel wheel has replaced the brass one, and if well made answers very well for the cheap grade of watches, but for accurate timekeeping it cannot be compared to the lever and chronometer escapements. Fig. 103 shows the escape wheel and cylinder in both the plan and elevation, while in Fig. 104 is shown the cylinder considerably enlarged for the sake of clearness. The plugs are shown removed to the better illustrate the method of inserting them. At the height where the escape teeth strike, half the cylinder is cut away, while just below it is cut away considerably more, so as to allow the balance to vibrate almost a whole turn. In the plan of Fig. 103 the cylinder and tooth is shown in the various stages of lifting. Immediately that the tooth has imparted the impulse it drops unto a portion of the cylinder, which is concentric to its axis. In Fig. 103 at the upper side of the escape wheel is shown a sectional view of the cylinder at the beginning of the impulse which will drive the balance around towards the right. In the second section the tooth has completed the impulse and dropped upon the interior locking surface, while in the following position it has continued around to the right until the completion of the vibration. The next action will be the returning of the cylinder to the position ready to receive the impulse which will cause the vibration in the opposite direction. This action of return is accomplished by the balance spring, which also at the same time unlocks the tooth, when the same action takes place in the opposite direction. The length of a tooth from the point which begins the impulse to that which ends it, measured in a straight line should be equal to the inside diameter of the cylinder, less the necessary amount for freedom, while the outside diameter of the cylinder should be equal to the space between the points of two teeth less the necessary amount for free action. From the above we see that there is a certain relation between the length of teeth and space between them, the inner and outer diameter of the cylinder and the thickness of the sides of the cylinder as well.