An Analysis of the Lever Escapement | Page 4

is struck from the pallet center A; the
interangles being equal, consequently the pallets must be equidistant.
The weak point of this pallet is that the lifting is not performed so
favorably; by examining the lifting planes MO and NP, we see that the
discharging edge, O, is closer to the center, A, than the discharging
edge, P; consequently the lifting on the engaging pallet is performed on
a shorter lever arm than on the disengaging pallet, also any inequality
in workmanship would prove more detrimental on the engaging than on
the disengaging pallet. The equidistant pallet requires fine
workmanship throughout. We have purposely shown it of a width of
10°, which is the widest we can employ in a 15 tooth wheel, and shows

the defects of this escapement more readily than if we had used a
narrow pallet. A narrower pallet is advisable, as the difference in the
discharging edges will be less, and the lifting arms would, therefore,
not show so much difference in leverage.
[Illustration: Fig. 3.]
The circular pallet is sometimes appropriately called "the pallet with
equal lifts," as the lever arms AMO and ANP, Fig. 3, are equal lengths.
It will be noticed by examining the diagram, that the pallets are
bisected by the 30° lines EB and FB, one-half their width being placed
on each side of these lines. In this pallet we have two locking circles,
MP for the engaging pallet, and NO for the disengaging pallet. The
weak points in this escapement are that the unlocking resistance is
greater on the engaging than on the disengaging pallet, and that neither
of them lock on the tangents AC and AD, at the points of intersection
with EB and FB. The narrower the circular pallet is made, the nearer to
the tangent will the unlocking be performed. In neither the equidistant
or circular pallets can the unlocking resistance be exactly the same on
each pallet, as in the engaging pallet the friction takes place before AB,
the line of centers, which is more severe than when this line has been
passed, as is the case with the disengaging pallet; this fact
proportionately increases the existing defects of the circular over the
equidistant pallet, and vice versa, but for the same reason, the lifting in
the equidistant is proportionately accompanied by more friction than in
the circular.
Both equidistant and circular pallets have their adherents; the finest
Swiss, French and German watches are made with equidistant
escapements, while the majority of English and American watches
contain the circular. In our opinion the English are wise in adhering to
the circular form. We think a ratchet wheel should not be employed
with equidistant pallets. By examining Fig. 2, we see an English pallet
of this form. We have shown its defects in such a wide pallet as the
English (as we have before stated), because they are more readily
perceived; also, on account of the shape of the teeth, there is danger of
the discharging edge, P, dipping so deep into the wheel, as to make

considerable drop necessary, or the pallets would touch on the backs of
the teeth. In the case of the club tooth, the latter is hollowed out,
therefore, less drop is required. We have noticed that theoretically, it is
advantageous to make the pallets narrower than the English, both for
the equidistant and circular escapements. There is an escapement,
Fig. 4, which is just the opposite to the English. The entire lift is
performed by the wheel, while in the case of the ratchet wheel, the
entire lifting angle is on the pallets; also, the pallets being as narrow as
they can be made, consistent with strength, it has the good points of
both the equidistant and circular pallets, as the unlocking can be
performed on the tangent and the lifting arms are of equal length. The
wheel, however, is so much heavier as to considerably increase the
inertia; also, we have a metal surface of quite an extent sliding over a
thin jewel. For practical reasons, therefore, it has been slightly altered
in form and is only used in cheap work, being easily made.
[Illustration: Fig. 4.]
We will now consider the drop, which is a clear loss of power, and, if
excessive, is the cause of much irregularity. It should be as small as
possible consistent with perfect freedom of action.
In so far as angular measurements are concerned, no hard and fast rule
can be applied to it, the larger the escape wheel the smaller should be
the angle allowed for drop. Authorities on the subject allow 1½° drop
for the club and 2° for the ratchet tooth. It is a fact that escape wheels
are not cut perfectly true; the teeth are apt to bend slightly from the