Fig. 92. Eight Day Hour and Half Hour Strike.
[Fig. 92] shows an eight-day, Seth Thomas movement, which strikes the hours on a count wheel train and the half hours from the center arbor. All the wheels, pinions, arbors, pins, levers and hooks are correctly shown in proper position, but the front plate has been left off for greater clearness. The reader will therefore be required to remember that the escape wheel, pallets, crutch, pendulum and the stud for the pendulum suspension are really fixed to the front plate, while in the drawing they have no visible means of support, because the plate is left off.
The time train occupies the right-hand side of the movement and the striking train the left hand. Running up the right-hand from the spring to the escape wheel, we find an extra wheel and pinion which is provided to secure the eight days’ run. We also see that what would ordinarily be the center arbor is up in the right corner and does not carry the hands; further, the train is bent over at a right angle, in order to save space and get the escape wheel in the center at the top of the movement. The striking train is also crowded down out of a straight line, the locking cam being to the right of the pin wheel and the warning wheel and fly as close to the center as possible. This leaves some space between the pin wheel and the intermediate wheel of the time train and here we find our center arbor, driven from the intermediate wheel by an extra pinion on the minute wheel arbor, the minute wheel meshing with the cannon pinion on the center arbor. This rearranging of trains to save space is frequently done and often shows considerable ingenuity and skill; it also will many times serve to identify the maker of a movement when its origin is a matter of doubt and we need some material, so that the planting of trains is not only a matter of interest, but should be studied, as familiarity with the methods of various factories is frequently of service to the watchmaker.
[Fig. 93] is the upper portion of the same striking train, drawn to a larger scale for the sake of clearness. It also shows the center arbor, both hammer tails and the stop on the hammer arbor, which strikes against the bottom of the front plate to prevent the hammer-spring from throwing the hammer out of reach of the pins. The pin wheel, R, and count wheel, E, are mounted close together and are about the same size, so that they are shown broken away for a part of their circumferences for greater clearness in explaining the action of the locking hook, C, and the locking cam, D.
[Fig. 94] shows the same parts in the striking position, being shown as just about to strike the last blow of 12. Similar parts have similar letters in both figures.
The count wheel, E, is loose on a stud in the plate, concentric with the arbor of the pin wheel, R. The pivot of R runs through this stud. The sole office of the count wheel is to regulate the distance to which the locking hook C, is allowed to fall. The count hook, A, and the locking hook, C, are mounted on the same arbor, B, so that they move in unison. If A is allowed to fall into a deep slot of the count wheel, C will fall far enough to engage the locking face of the cam D and stop the train, as in [Fig. 93]. If, on the contrary, A drops on the rim of the wheel, C will be held out of the locking position as D comes around ([see Fig. 94]), and the train will keep on running. It will be seen that after passing the locking notch, D, [Fig. 94], will in its turn raise the hook C, which will ride on the edge of D, and hold A clear of the count wheel until the locking notch of D is again reached, when a deep notch in the wheel will allow C to catch, as in [Fig. 93], unless C is stopped by A falling on the rim of the wheel, as in [Fig. 94].
Fig. 93. Upper Portion of Striking Train Locked.