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

33 страница из 100

Fig. 6. Cast iron bracket for heavy pendulums and movements.

If so heavy a pendulum is deemed undesirable, the bob would have to be made of cylindrical form, retaining the height, as necessary to compensation, and varying the diameter of the cylinder to suit the weight desired.

Fig. 7. Wood rod Fig. 8. Bob of metal casing

and lead bob.filled with shot.

Wood Rod and Lead Bob.—The wood should be clear, straight-grained and thoroughly dried, then given several coats of shellac varnish, well baked on. It may be either flat, oval or round in section, but is generally made round because the brass cap at the upper end, the lining for the crutch, and the ferrule for the adjusting screw at the lower end may then be readily made from tubing. For pendulums smaller than one second, the wood is generally hard, as it gives a firmer attachment of the metal parts.

Inches. Length, top of suspension spring to bottom of bob 44.5 Length to bottom of nut 45.25 Diameter of bob 2.0 Length of bob 10.5 Weight of bob, 8 lbs. Acting length of suspension spring 1.0 Width of spring .45 Thickness .008 Diameter of rod .5

The top of the rod should have a brass collar fixed on it by riveting through the rod and it should extend down the rod about three inches, so as to make a firm support for the slit to receive the lower clip of the suspension spring. The lower end should have a slit or a round hole drilled longitudinally three inches up the rod to receive the upper end of the adjusting screw and this should also fit snugly and be well pinned or riveted in place. ssss1. A piece of thin brass tube about one inch in length is fitted over the rod where the crutch works.