An Analysis of the Lever Escapement | Page 8

treating the subject from a purely
horological standpoint, and neither patriotism or prejudice has anything
to do with it. We wish to sift the matter thoroughly and arrive at a just
conception of the merits and defects of each form of escapement, and
show reasons for our conclusions.
[Illustration: Fig. 11.]
[Illustration: Fig. 12.]
[Illustration: Fig. 13.]
Anyone who has closely followed our deductions must see that in so far
as the wheel is concerned the ratchet or English wheel has several
points in its favor. Such a wheel is inseparable from a wide pallet; but
we have seen that a narrower pallet is advisable; also as little drop and
lock as possible; clearly, we must effect a compromise. In other words,
so far the balance of our reasoning is in favor of the club tooth
escapement and to effect an intelligent division of angles for tooth,

pallet and lift is one of the great questions which confronts the
intelligent horologist.
Anyone who has ever taken the pains to draw pallet and tooth with
different angles, through every stage of the lift, with both wide and
narrow pallets and teeth, in circular and equidistant escapements, will
have received an eye-opener. We strongly advise all our readers who
are practical workmen to try it after studying what we have said. We
are certain it will repay them.
[Illustration: Fig. 2.]
The Center Distance of Wheel and Pallets. The direction of pressure of
the wheel teeth should be through the pallet center by drawing the
tangents AC and AD, Fig. 2 to the primitive circle GH, at the
intersection of the angle FBE. This condition is realized in the
equidistant pallet. In the circular pallet, Fig. 3, this condition cannot
exist, as in order to lock on a tangent the center distance should be
greater for the engaging and less for the disengaging pallet, therefore
watchmakers aim to go between the two and plant them as before
specified at A.
When planted on the tangents the unlocking resistance will be less and
the impulse transmitted under favorable conditions, especially so in the
circular, as the direction of pressure coincides (close to the center of the
lift), with the law of the parallelogram of forces.
It is impossible to plant pallets on the tangents in very small
escapements, as there would not be enough room for a pallet arbor of
proper strength, nor will they be found planted on the tangents in the
medium size escapement with a long pallet arbor, nor in such a one
with a very wide tooth (see Fig. 4) as the heel would come so close to
the center A, that the solidity of pallets and arbor would suffer. We will
give an actual example. For a medium sized escape wheel with a
primitive diameter of 7.5 mm., the center distance AB is 4.33 mm. By
using 3° of a lifting angle on the teeth, the distance from the heel of the
tooth to the pallet center will be .4691 mm.; by allowing .1 mm.
between wheel and pallet and .15 mm. for stock on the pallets we find

we will have a pallet arbor as
follows: .4691 - (.1 + .15) × 2 = .4382 mm. It would not be practicable
to make anything smaller.
[Illustration: Fig. 3.]
It behooves us now to see that while a narrow pallet is advisable a very
wide tooth is not; yet these two are inseparable. Here is another case for
a compromise, as, unquestionably the pallets ought to be planted on the
tangents. There is no difficulty about it in the English lever, and we
have shown in our example that a judiciously planned club tooth
escapement of medium size can be made with the center distance
properly planted.
[Illustration: Fig. 4.]
When considering the center distance we must of necessity consider the
widths of teeth and pallets and their lifting angles. We are now at a
point in which no watchmaker of intelligence would indicate one
certain division for these parts and claim it to be "the best." It is always
those who do not thoroughly understand a subject who are the first to
make such claims. We will, however, give our opinion within certain
limits. The angle to be divided for tooth and pallet is 10½°. Let us
divide it by 2, which would be the most natural thing to do, and
examine the problem. We will have 5¼° each for width of tooth and
pallet. We must have a smaller lifting angle on the tooth than on the
pallet, but the wider the tooth the greater should its lifting angle be. It
would not be mechanical to make the tooth wide and the lifting angle
small, as the lifting plane on the pallets would be too steep on account