The American watchmaker and jeweler; an encyclopedia for the horologist, jeweler, gold and silversmith .. . he diameter of the one in which theimpulse pin is fixed, is mounted on the balance-staff for the purposeand a small gold finger, projecting far enough to reach the edge of thesmaller roller, is screwed to the lever. The safety roller should not beless than half the diameter of the impulse roller, for the smaller thesafety roller, the farther the safety finger enters the crescent before theruby pin enters the notch of the lever; and, as directly the safety fingerenters the crescent, the i
The American watchmaker and jeweler; an encyclopedia for the horologist, jeweler, gold and silversmith .. . he diameter of the one in which theimpulse pin is fixed, is mounted on the balance-staff for the purposeand a small gold finger, projecting far enough to reach the edge of thesmaller roller, is screwed to the lever. The safety roller should not beless than half the diameter of the impulse roller, for the smaller thesafety roller, the farther the safety finger enters the crescent before theruby pin enters the notch of the lever; and, as directly the safety fingerenters the crescent, the impulse pin must be within the horn of the leverthe smaller the safety roller, the longer must be the horn. Then, if thehorns are excessively long, the extent of the free vibration of the balanceis curtailed, because the ruby pin touches the outside of the lever will be seen that in the single roller escapement (Fig. 201) the safetypin does not enter the crescent before the ruby pin enters the notch,and, therefore, in the single roller escapement the lever really requires 225 Lever but the smallest possible amount of horn. Fig. 201 shows the doubleroller arrangement. Here it will be seen that the safety finger entersthe crescent some time before the ruby pin gets to the notch. Duringthis interval, should the hands of the watch be set back, the pallets couldnot trip, for the horn of the lever would be caught on the ruby pin. I have tried to explain thisfully, because doubleroller escapements occa-sionally fail to give satis-faction owing to the ,lever having insufficienthorn. On the otherhand, the levers of singleroller escapements,where scarcely any hornis required, are oftenFig. 201. made with long ones. Besides getting a sound safety action with small balance arc, the dou-ble roller has three other advantages, (i) The impulse is given morenearly on the line of centers, and consequently with less engaging fric-tion. (2) The safety roller being of a lesser
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Keywords: ., bookcentury1800, bookdecade1890, bookidamericanwatc, bookyear1892
