An Analysis of the Lever Escapement | Page 9

of being narrow. A lifting angle on the tooth which would be exactly
suitable for a given circular, would be too great for a given equidistant
pallet. It follows, therefore, taking 5¼° as a width for the tooth, that
while we could employ it in a fair sized escapement with equidistant
pallets, we could not do so with circular pallets and still have the latter
pitched on the tangents. We see the majority of escapements made with
narrower teeth than pallets, and for a very good reason.
In the example previously given, the 3° lift on the tooth is well adapted

for a width of 4½°, which would require a pallet 6° in width. The tooth,
therefore, would be ¾ the width of pallets, which is very good indeed.
From what we have said it follows that a large number of pallets are not
planted on the tangents at all. We have never noticed this question in
print before. Writers generally seem to, in fact do, assume that no
matter how large or small the escapement may be, or how the pallets
and teeth are divided for width and lifting angle, no difficulty will be
found in locating the pallets on the tangents. Theoretically there is no
difficulty, but in practice we find there is.
Equidistant vs. Circular. At this stage we are able to weigh the circular
against the equidistant pallet. In beginning this essay we had to explain
the difference between them, so the reader could follow our discussion,
and not until now, are we able to sum up our conclusions.
The reader will have noticed that for such an important action as the lift,
which supplies power to the balance, the circular pallet is favored from
every point of view. This is a very strong point in its favor. On the
other hand, the unlocking resistance being less, and as nearly alike as
possible on both pallets in the equidistant, it is a question if the total
vibration of the balance will be greater with the one than the other,
although it will receive the impulse under better conditions from the
circular pallet; but it expends more force in unlocking it. Escapement
friction plays an important role in the position and isochronal
adjustments; the greater the friction encountered the slower the
vibration of the balance. The friction should be constant. In unlocking,
the equidistant comes nearer to fulfilling this condition, while during
the lift it is more nearly so in the circular. The friction in unlocking,
from a timing standpoint, overshadows that of the impulse, and the
tooth can be a little wider in the equidistant than the circular
escapement with the pallet properly planted. Therefore for the finest
watches the equidistant escapement is well adapted, but for anything
less than that the circular should be our choice.
The Fork and Roller Action. While the lifting action of the lever
escapement corresponds to that of the cylinder, the fork and roller
action corresponds to the impulse action in the chronometer and duplex

escapements.
Our experience leads us to believe that the action now under
consideration is but imperfectly understood by many workmen. It is a
complicated action, and when out of order is the cause of many
annoying stoppages, often characterized by the watch starting when
taken from the pocket.
The action is very important and is generally divided into impulse and
safety action, although we think we ought to divide it into three,
namely, by adding that of the unlocking action. We will first of all
consider the impulse and unlocking actions, because we cannot
intelligently consider the one without the other, as the ruby pin and the
slot in the fork are utilized in each. The ruby pin, or strictly speaking,
the "impulse radius," is a lever arm, whose length is measured from the
center of the balance staff to the face of the ruby pin, and is used, firstly,
as a power or transmitting lever on the acting or geometrical length of
the fork (i. e., from the pallet center to the beginning of the horn), and
which at the moment is a resistance lever, to be utilized in unlocking
the pallets. After the pallets are unlocked the conditions are reversed,
and we now find the lever fork, through the pallets, transmitting power
to the balance by means of the impulse radius. In the first part of the
action we have a short lever engaging a longer one, which is an
advantage. See Fig. 14, where we have purposely somewhat
exaggerated the conditions. A'X represents the impulse radius at
present under discussion, and AW the acting length of the fork. It will
be seen that the shorter the impulse radius, or in other words, the closer
the ruby pin is to the balance staff and the