Watch and Clock Escapements. Anonymous

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      Again, it follows as a self-evident fact, if the pallet we are dealing with was locked, that is, engaged with the tooth D'', the inner angle n of the exit pallet would be one and a half degrees inside the pitch circle a. With the dividers set at 5", we sweep the short arc b b, and from the intersection of this arc with the line B c we lay off ten degrees, and through the point so established, from B, we draw the line B d. Below the point of intersection of the line B d with the short arc b b we lay off one and a half degrees, and through the point thus established we draw the line B e.

      LOCATING THE INNER ANGLE OF THE EXIT PALLET.

      The intersection of the line B e with the arc h, which we will term the point n, represents the location of the inner angle of the exit pallet. We have already explained how we located the position of the outer angle at o. We draw the line n o and define the impulse face of the exit pallet. If we mentally analyze the problem in hand, we will see that as the exit pallet vibrates through its ten degrees of arc the line B d and B c change places, and the tooth D'' locks one and a half degrees. To delineate the locking face of the exit pallet, we erect a perpendicular to the line B e from the point n, as shown by the line n p.

      From n as a center we sweep the short arc t t, and from its intersection with the line n p we lay off twelve degrees, and through the point so established we draw the line n u, which defines the locking face of the exit pallet. We draw the line o o' parallel with n u and define the outer face of said pallet. In Fig. 21 we have not made any attempt to show the full outline of the pallets, as they are delineated in precisely the same manner as those previously shown.

      We shall next describe the delineation of a club-tooth escapement with pallets having equidistant locking faces; and in Fig. 22 we shall show pallets with much wider arms, because, in this instance, we shall derive more of the impulse from the pallets than from the teeth. We do this to show the horological student the facility with which the club-tooth lever escapement can be manipulated. We wish also to impress on his mind the facts that the employment of thick pallet arms and thin pallet arms depends on the teeth of the escape wheel for its efficiency, and that he must have knowledge enough of the principles of action to tell at a glance on what lines the escapement was constructed.

      Suppose, for illustration, we get hold of a watch which has thin pallet arms, or stones, if they are exposed pallets, and the escape was designed for pallets with thick arms. There is no sort of tinkering we can do to give such a watch a good motion, except to change either the escape wheel or the pallets. If we know enough of the lever escapement to set about it with skill and judgment, the matter is soon put to rights; but otherwise we can look and squint, open and close the bankings, and tinker about till doomsday, and the watch be none the better.

      CLUB-TOOTH LEVER WITH EQUIDISTANT LOCKING FACES.

      In drawing a club-tooth lever escapement with equidistant locking, we commence, as on former occasions, by producing the vertical line A k, Fig. 22, and establishing the center of the escape wheel at A, and with the dividers set at 5" sweep the pitch circle a. On each side of the intersection of the vertical line A k with the arc a we set off thirty degrees on said arc, and through the points so established draw the radial lines A b and A c.

      From the intersection of the radial line A b with the arc a lay off three and a half degrees to the left of said intersection on the arc a, and through the point so established draw the radial line A e. From the intersection of the radial line A b with the arc a erect the perpendicular line f, and at the crossing or intersection of said line with the vertical line A k establish the center of the pallet staff, as indicated by the small circle B. From B as a center sweep the short arc l with a 5" radius; and from the intersection of the radial line A b with the arc a continue the line f until it crosses the short arc l, as shown at f'. Lay off one and a half degrees on the arc l below its intersection with the line f', and from B as a center draw the line B i through said intersection. From B as a center, through the intersection of the radial line A b and the arc a, sweep the arc g.

      The space between the lines B f' and B i on the arc g defines the extent of the locking face of the entrance pallet C. The intersection of the line B f' with the arc g we denominate the point o, and from this point as a center sweep the short arc p with a 5" radius; and on this arc, from its intersection with the radial line A b, lay off twelve degrees, and through the point so established, from o as a center, draw the radial line o m, said line defining the locking face of the entrance pallet C.

      It will be seen that this gives a positive "draw" of twelve degrees to the entrance pallet; that is, counting to the line B f'. In this escapement as delineated there is perfect tangential locking. If the locking face of the entrance-pallet stone at C was made to conform to the radial line A b, the lock of the tooth D at o would be "dead"; that is, absolutely neutral. The tooth D would press the pallet C in the direction of the arrow x, toward the center of the pallet staff B, with no tendency on the part of the pallet to turn on its axis B. Theoretically, the pallet with the locking face cut to coincide with the line A b would resist movement on the center B in either direction indicated by the double-headed arrow y.

      A pallet at C with a circular locking face made to conform to the arc g, would permit movement in the direction of the double-headed arrow y with only mechanical effort enough to overcome friction. But it is evident on inspection that a locking face on the line A b would cause a retrograde motion of the escape wheel, and consequent resistance, if said pallet was moved in either direction indicated by the double-headed arrow y. Precisely the same conditions obtain at the point u, which holds the same relations to the exit pallet as the point o does to the entrance pallet C.

      ANGULAR MOTION OF ESCAPE WHEEL DETERMINED.

      The arc (three and a half degrees) of the circle a embraced between the radial lines A b and A e determines the angular motion of the escape wheel utilized by the escape-wheel tooth. To establish and define the extent of angular motion of the escape wheel utilized by the pallet, we lay off seven degrees on the arc a from the point o and establish the point n, and through the point n, from B as a center, we sweep the short arc n'. Now somewhere on this arc n' will be located the inner angle of the entrance pallet. With a carefully-made drawing, having the escape wheel 10" in diameter, it will be seen that the arc a separates considerably from the line, B f' where it crosses the arc n'.

      It will be remembered that when drawing the ratchet-tooth lever escapement a measurement of eight and a half degrees was made on the arc n' down from its intersection with the pitch circle, and thus the inner angle of the pallet was located. In the present instance the addendum line w becomes the controlling arc, and it will be further noticed on the large drawing that the line B h at its intersection with the arc n' approaches nearer to the arc w than does the line B f' to the pitch circle a; consequently, the inner angle of the pallet should not in this instance be carried down on the arc n' so far to correct the error as in the ratchet tooth.

      Reason tells us that if we measure ten degrees down on the arc n' from its intersection with the СКАЧАТЬ