An Analysis of the Lever Escapement | Page 6

it is sometimes called, "the slide," should also
be as light as possible; from ¼° to ½° is sufficient. It follows then, the
bankings should be as close together as possible, consistent with
requisite freedom for escaping. Anything more than this increases the
angular connection of the balance with the escapement, which directly
violates the theory under which it is constructed; also, a greater amount
of work will be imposed upon the balance to meet the increased
unlocking resistance, resulting in a poor motion and accurate time will
be out of the question. It will be seen that those workmen who make a
practice of opening the banks, "to give the escapement more freedom"
simply jump from the frying pan into the fire. The bankings should be
as far removed from the pallet center as possible, as the further away
they are pitched the less run we require, according to angular

measurement. Figure 6 illustrates this fact; the tooth S has just dropped
on the engaging pallet, but the fork has not yet reached the bankings.
At a we have 1° of run, while if placed at b we would only have ½° of
run, but still the same freedom for escaping, and less unlocking
resistance.
The bankings should be placed towards the acting end of the fork as
illustrated, as in case the watch "rebanks" there would be more strain
on the lever pivots if they were placed at the other end of the fork.
[Illustration: Fig. 7.]
The Lift.--The lift is composed of the actual lift on the teeth and pallets
and the lock and run. We will suppose that from drop to drop we allow
10°; if the lock is 1½° then the actual lift by means of the inclined
planes on teeth and pallets will be 8½°. We have seen that a small
lifting angle is advisable, so that the vibrations of the balance will be as
free as possible. There are other reasons as well. Fig. 7 shows two
inclined planes; we desire to lift the weight 2 a distance equal to the
angle at which the planes are inclined; it will be seen at a glance that
we will have less friction by employing the smaller incline, whereas
with the larger one the motive power is employed through a greater
distance on the object to be moved. The smaller the angle the more
energetic will the movement be; the grinding of the angles and fit of the
pivots, etc., also increases in importance. An actual lift of 8½° satisfies
the conditions imposed very well. We have before seen that both on
account of the unlocking and the lifting leverage of the pallet arms, it
would be advisable to make them narrow both in the equidistant and
circular escapement. We will now study the question from the
standpoint of the lift, in so far as the wheel is concerned.
[Illustration: Fig. 8.]
It is self-evident that a narrow pallet requires a wide tooth, and a wide
pallet a narrow or thin tooth wheel; in the ratchet wheel we have a
metal point passing over a jeweled plane. The friction is at its minimum,
because there is less adhesion than with the club tooth, but we must
emphasize the fact that we require a greater angle in proportion on the

pallets in this escapement than with the narrow pallets and wider tooth.
This seems to be a point which many do not thoroughly comprehend,
and we would advise a close study of Fig. 8, which will make it
perfectly clear, as we show both a wide and a narrow pallet. GH,
represents the primitive, which in this figure is also the real diameter of
the escape wheel. In measuring the lifting angles for the pallets, our
starting point is always from the tangents AC and AD. The tangents are
straight lines, but the wheel describes the circle GH, therefore they
must deviate from one another, and the closer to the center A the
discharging edge of the engaging pallet reaches, the greater does this
difference become; and in the same manner the further the discharging
edge of the disengaging pallet is from the center A the greater it is. This
shows that the loss is greater in the equidistant than in the circular
escapement. After this we will designate this difference as the "loss." In
order to illustrate it more plainly we show the widest pallet--the
English--in equidistant form. This gives another reason why the
English lever should only be made with circular pallets, as we have
seen that the wider the pallet the greater the loss. The loss is measured
at the intersection of the path of the discharging edge OO, with the
circle G H, and is shown through AC2, which intersects these circles at
that