Читать книгу The Modern Clock. A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair онлайн

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Now that the pendulum is all ready to balance on the knife edge, proceed as in the case of the simple pendulum, and ascertain at what point up the rod the spring must be placed. In this pendulum the rod will be heavier in proportion than the wood rod was to its bob, and the center of gravity of the whole will be found higher up in the bob. However, wherever in the bob the center of gravity is found, that is the starting point to measure from to find the total length of the rod, and the point for the spring. The heavier the rod is in relation to the bob, the higher will the center of gravity of the whole rise in the bob, and the greater will be the total length of the entire pendulum.

In getting up a rod of the kind just described, the main item is to get the parts all so arranged that there will be very little settling of the joints in contact, particularly those which sustain the weight of the bob and the whole dead weight of the pendulum. The nut in the center of the pendulum holds the weight of the bob only, but it should fit against the shoulder formed for the purpose by the juncture of the two holes, and the face of the nut should be turned true and flat, so that there may not be any uneven motion, and only the one imparted by the progressive one of the threads. When this nut is put to its place for the last time, and after all is finished, there should be a little tallow put on to the face of the nut just where it comes to a seat against the shoulder of the bob, as this shoulder being not very well finished, the two surfaces coming in contact, if left dry, might cut and tear each other, and help to make the nut’s action slightly unsteady and unreliable. A finished washer can be driven into this lower hole up to the center, friction-tight, and serve as a reliable and finished seat for the nut.