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 addendum circle w we must define the position of the inner angle of the entrance pallet. We name the point so established the point r. The outer angle of this pallet is located at the intersection of the radial line A b with the line B i; said intersection we name the point v. Draw a line from the point v to the point r, and we define the impulse face of the entrance pallet; and the angular motion obtained from it as relates to the pallet staff embraces six degrees.
Measured on the arc l, the entire ten degrees of angular motion is as follows: Two and a half degrees from the impulse face of the tooth, and indicated between the lines B h and B f; one and a half degrees lock between the lines B f’ and B i; six degrees impulse from pallet face, entrance between the lines B i and B j.
A DEPARTURE FROM FORMER PRACTICES.
Grossmann and Britten, in all their delineations of the club-tooth escapement, show the exit pallet as disengaged. To vary from this beaten track we will draw our exit pallet as locked. There are other reasons which prompt us to do this, one of which is, pupils are apt to fall into a rut and only learn to do things a certain way, and that way just as they are instructed.