Watch and Clock Escapements / A Complete Study in Theory and Practice of the Lever, Cylinder and Chronometer Escapements, Together with a Brief Account of the Origin and Evolution of the Escapement in Horology

by Anonymous

DELINEATING AN ESCAPE-WHEEL TOOTH WHILE IN ACTION.

We will now go through the operation of delineating an escape-wheel tooth while in action. The position we shall assume is the one in which the cylinder and escape-wheel tooth are in the relation of the passage of half the impulse face of the tooth into the cylinder. To do this is simple enough: We first produce the arcs a b c, Fig. 133, as directed, and then proceed to delineate a tooth as in previous instances. To delineate our cylinder in the position we have assumed above, we take the space between the points e d in our dividers and setting one leg at d establish the point g, to represent the center of our cylinder. If we then sweep the circle h from the center of g we define the inner surface of the shell of our cylinder.

Strictly speaking, we have not assumed the position we stated, that is, the impulse face of the tooth as passing half way into the cylinder. To comply strictly with our statement, we divide the chord of the impulse face of the tooth A into eight equal spaces, as shown. Now as each of these spaces represent the thickness of the cylinder, if we take in our dividers four of these spaces and half of another, we have the radius of a circle passing the center of the cylinder shell. Consequently, if with this space in our dividers we set the leg at d, we establish on the arc b the point i. We locate the center of our cylinder when one-half of an entering tooth has passed into the cylinder. If now from the new center with our dividers set at four of the spaces into which we have divided the line e f we can sweep a circle representing the inner surface of the cylinder shell, and by setting our dividers to five of these spaces we can, from i as a center, sweep an arc representing the outside of the cylinder shell. For all purposes of practical study the delineation we show at Fig. 133 is to be preferred, because, if we carry out all the details we have described, the lines would become confused. We set our dividers at five of the spaces on the line e f and from g as a center sweep the circle j, which delineates the outer surface of our cylinder shell.

Let us now, as we directed in our former instructions, draw a flattened curve to represent the acting surface of the entrance lip of our cylinder as if it were in direct contact with the impulse face of the tooth. To delineate the exit lip we draw from the center g, Fig. 134, to the radial line g k, said line passing through the point of contact between the tooth and entrance lip of the cylinder. Let us next continue this line on the opposite side of the point g, as shown at g k', and we thus bisect the cylinder shell into two equal parts of 180 degrees each. As we previously explained, the entire extent of the cylinder half shell is 196 degrees. We now set our dividers to the radius of any convenient arc which we have divided into degrees, and from g as a center sweep the short arc l l, and from the intersection of this arc with the line g k' we lay off sixteen degrees on the said arc l and establish the point n, from g as a center draw the radial line g n'. Take ten degrees from the same parent arc and establish the point m, then draw the line g m'. Now the arc on the circles h j between the lines g n' and g m limits the extent of the exit lip of the cylinder and the arc between the lines g k' and g m' represents the locking surface of the cylinder shell.

To delineate the U arms we refer to Fig. 135. Here, again, we draw the arc a b c and delineate a tooth as before. From the point e located at the heel of the tooth we draw the radial line e e'. From the point e we lay off on the arc a five degrees and establish the point p; we halve this space and draw the short radial line p' s' and p s. From the point e on the arc A we lay off twenty-four degrees and establish the point t, which locates the heel of the next tooth in advance of A. At two and a half degrees to the right of the point t we locate the point r and draw the short radial line r s. On the arc b and half way between the lines p s and r s, we establish the point u, and from it as a center we sweep the arc v defining the curve of the U arms.

We have now given minute instructions for drawing a cylinder escapement in all its details except the extent of the banking slot of the cylinder, which is usually made to embrace an angular extent of 270 degrees; consequently, the pillar of the cylinder will not measure more than ninety degrees of angular extent.

There is no escapement constructed where carefully-made drawings tend more to perfect knowledge of the action than the cylinder. But it is necessary with the pupil to institute a careful analysis of the actions involved. In writing on a subject of this kind it is extremely perplexing to know when to stop; not that there is so much danger of saying too much as there is not having the words read with attention.

As an illustration, let us consider the subject of depth between the cylinder and the escape wheel. As previously stated, 196 degrees of cylinder shell should be employed; but suppose we find a watch in which the half shell has had too much cut away, so the tooth on entering the half shell after parting with the entrance lip does not strike dead on the inside of the shell, but encounters the edge of the exit lip. In this case the impulse of the balance would cause the tooth to slightly retrograde and the watch would go but would lack a good motion. In such an instance a very slight advance of the chariot would remedy the fault—not perfectly remedy it, but patch up, so to speak—and the watch would run.