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Watch and Clock Escapements eBook

This eBook from the Gutenberg Project consists of approximately 202 pages of information about Watch and Clock Escapements.
able to resist, without buckling or cockling, the thrust of the escape wheel, represented by the arrows p o.  Now we can readily understand that the lighter we make the parts i j k m, the weaker the spring h can be.  You say, perhaps, if we make it too weak it will be liable to buckle under the pressure of the escape wheel; this, in turn, will depend in a great measure on the condition of the spring h.  Suppose we have it straight when we put it in position, it will then have no stress to keep it pressed to the holding, stop or banking screw, which regulates the lock of the tooth.  To obtain this stress we set the foot F of the detent around to the position indicated by the dotted lines r and n, and we get the proper tension on the detent spring to effect the lock, or rather of the detent in time to lock the escape wheel; but the spring h, instead of being perfectly straight, is bent and consequently not in a condition to stand the thrust of the escape wheel, indicated by the arrows o p.

OBTAINING THE BEST CONDITIONS.

Now the true way to obtain the best conditions is to give the spring h a set curvature before we put it in place, and then when the detent is in the proper position the spring h will have tension enough on it to bring the jewel s against the stop screw, which regulates the lock, and still be perfectly straight.  This matter is of so much importance that we will give further explanation.  Suppose we bend the detent spring h so it is curved to the dotted line t, Fig. 136, and then the foot F would assume the position indicated at the dotted line r.  We next imagine the foot F to be put in the position shown by the full lines, the spring h will become straight again and in perfect shape to resist the thrust of the escape wheel.

Little “ways and methods” like the above have long been known to the trade, but for some reason are never mentioned in our text books.  A detent spring 2/1000” thick and 80/1000” wide will stand the thrust for any well-constructed marine chronometer in existence, and yet it will not require half a pennyweight to deflect it one-fourth of an inch.  It is a good rule to make the length of the detent from the foot F to the center of the locking jewel pipe j equal to the diameter of the escape wheel, and the length of the detent spring h two-sevenths of this distance.  The length of the horn k is determined by the graphic plan and can be taken from the plotted plan.  The end, however, should approach as near to the discharging jewel as possible and not absolutely touch.  The discharging (gold) spring m is attached to the blade i of the detent with a small screw l cut in a No. 18 hole of a Swiss plate.  While there should be a slight increase in thickness in the detent blade at w, where the gold spring is attached, still it should be no more than to separate the gold spring m from the detent blade i.

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