We again lay off two and a half degrees from the intersection of the line A b with the arc a, but this time to the right of said intersection, and through the point so established, and from B as a center, we sweep the arc e. From the intersection of the radial line A g with the arc a we lay off to the left five and a half degrees on said arc, and through the point so established draw the radial line A f. With the dividers set at five inches we sweep the short arc m from B as a center. From the intersection of the line h B h’ with the arc m we lay off on said arc and above the line h’ four and a half degrees, and through the point so established draw the line B j.
We next set the dividers so they embrace the space on the radial line A b between its intersection with the line B j and the center A, and from A as a center sweep the arc i, said arc defining the addendum of the escape-wheel teeth. We draw a line from the intersection of the radial line A f with the arc i to the intersection of the radial line A g with the arc a, and thus define the impulse face of the escape-wheel tooth D. For defining the locking face of the tooth we draw a line at an angle of twenty-four degrees to the line A g, as previously described. The back of the tooth is defined with a curve swept from some point on the addendum circle i, such as our judgment will dictate.
In the drawing shown at Fig. 20 the radius of this curve was obtained by taking eleven and a half degrees from the degree arc of 5” radius in the dividers, and setting one leg at the intersection of the radial line A f with the arc i, and placing the other on the line i, and allowing the point so established to serve as a center, the arc was swept for the back of the tooth, the small circle at n denoting one of the centers just described. The length for the face of the tooth was obtained by taking eleven degrees from the degree arc just referred to and laying that space off on the line p, which defined the face of the tooth. The line B k is laid off one and a half degrees below B h on the arc m. The extent of this arc on the arc d defines the locking face of the entrance pallet. We set off four degrees on the arc m below the line B k, and through the point so established draw the line B l. We draw a line from the intersection of the line A g with the line c h to the intersection of the arc e with the line c l, and define the impulse face of the entrance pallet.
RELATIONS OF THE SEVERAL PARTS.
Before we proceed to delineate the exit pallet of our escapement, let us reason on the relations of the several parts.