The curved lever is double, and the pinion segment turns loosely between the halves and on the shaft, A; it is held up in its place by a light spring, F; the weight, E, is also held between the two halves of the double lever.
Fig. 88. Maintaining Power.
The action is as follows: The end of the lever, B, covers the end of the winding shaft so that it is necessary to raise it before putting the key on the winding shaft; it is raised till it strikes a stop, and then pushed in till the pinion segment engages with the going wheel of the train, when the weight, E, acting through the levers, furnishes power to drive the clock train while the going weight is being wound up. Of course the weight on the maintaining power must be so proportioned to the leverage that it will be equal to the power of the going barrel and its weight, a simple proposition in mechanics.
The number of teeth on the pinion segment, C, is sufficient to maintain power for fifteen minutes, at the end of which time the lever, B, will come down and again cover the end of the winding shaft; or, it may be pumped out of gear and dropped down. In case it is forgotten, the spring, F, will allow the segment to pass out of gear of itself and will simply allow it to give a click as it slips over each tooth in the going wheel; if this were not provided for, it would stop the clock.
CHAPTER XVI.
MOTION WORK AND STRIKING TRAINS.
Motion work is the name given to the wheels and pinions used to make the hour hand go once around the dial while the minute hand goes twelve times. Here a few preliminary observations will do much toward clearing up the operations of the trains. The reader will recollect that we started at a fixed point in the time train, the center arbor which must revolve once per hour, and increased this motion by making the larger wheels drive the smaller (pinions) until we reached sixty or more revolutions of the escape wheel to one of the center arbor. This gearing to increase speed is called “gearing up” and in it the pinions are always driven by the wheels. In the case of the hour hand we have to obtain a slowing effect and we do so by making the smaller wheels (pinions) drive the larger ones. This is called “gearing back” and it is the only place in the clock where this method of gearing occurs.