THE DETACHED LEVER ESCAPEMENT AS APPLIED TO CLOCKS.
As the clock repairer is almost of necessity a watchmaker, or hopes to
become one, and as he must enter deeply into the study of all questions
pertaining to the detached lever in its various forms before he can
make any progress at all in watchmaking, it would seem unnecessary to
repeat in these pages that which has already been so well said and
so perfectly drawn, described and illustrated by such authorities as
Moritz Grossman, Britten, Playtner and the various teachers in the
horological schools, to say nothing of an equally brilliant and more
numerous coterie of writers among the French, Germans and Swiss, so
that the reader is referred to these writers for the mathematics and
drawings which already so fully cover the technical and theoretical
properties of the detached lever escapement. A few words as to its
adaptation to clocks may, however, not be out of place.
Anyone who sees the clocks of to-day would be inclined to suppose
that the first clocks were constructed with pendulums, because this
is evidently the most simple and reliable system for clocks, and that
the employment of the balance has been suggested by the necessity for
portable time pieces. This is, however, not the case, for the first
clocks had a verge escapement with a crude balance consisting of two
arms, carrying shifting weights for regulation. The pendulum was not
used until about three hundred years after the invention of the first
clock.
After the invention of the dead beat escapement, with its great gain
in accuracy by the reduction of the arc of pendulum oscillation,
attempts were made to combine its many virtues with the necessarily
large vibrations of a balance and thus get all the advantages of
both systems. By placing the lever on the arbor of the anchor, it
was possible to multiply the small angle of impulse on the pallets
very considerably at the balance, and to make all connection between
them cease immediately after the impulse had been given. The dead
beat escapement was thus converted into the detached lever escapement
and the latter made available for both watches and clocks. Another
important feature of this escapement is that when properly proportioned
it will not set on the locking or lifting, but will start to go as soon
as power is applied to the escape wheel through the train. This cannot
be said of the cylinder, duplex, or detent escapements, and it will
be seen at once that this has an important influence upon the cost of
construction, which must always be considered in the manufacture of
cheap clocks in enormous quantities.
[Illustration: Fig. 61. Pin Escapement for Clocks.]
The lever escapement with pins for pallets and the lifting planes
on the teeth of the escape wheel, which is the one usually put into
cheap clocks, is from the theoretical point of view a very perfect
form, because its lifting and locking take place at exactly the same
center distance and at the same angles, which again allows for greater
latitude in cheap construction, while still maintaining a reasonably
accurate rate of performance. These are the main reasons why the pin
anchor has such universal use in cheap clocks.
As this escapement is generally centered between the plates, banking
pins are dispensed with by extending the counterpoise end of the lever
far enough so that its crescent shaped sides will perform that office
by banking against the scape wheel arbor; see Fig. 61. The fork end of
the lever engages with an impulse pin carried in the balance and the
balance arbor is cut away to pass the guard point or dart, thus doing
away with the roller table. In other constructions the roller table is
supplied in the shape of a small brass collet which carries the pin and
has a notch for the guard point, thus making a single roller escapement.
The diameter of the lifting pins is generally made equal to 2½ degrees
of the scape wheel, which gives a lift of 2 degrees on the pallet arms,
and the remainder of the lift, 6½ degrees, must be performed by the
lifting planes of the wheel teeth. The front sides of the wheel teeth
are generally made with 15 degrees of draw and the lever should bank
when the center of the pin is just a little past the locking corner of
the tooth. Other details of the pin anchor escapement coincide with the
ordinary pallet form, as used in watches, and the reader is referred
for them to the works of the various authors mentioned previously.
The trouble with the majority of these clocks is in the escapement and
balance pivots, and to these parts are we going to direct particular
attention, for often, be it ever so clean, the balance gets up a sort
of “caterpillar motion” that is truly distressing, and if no more is
done we may expect a “come back” job in a very short time. In taking
down the movement the face wheels are left in place, but sometimes
it may be necessary to remove the “set wheel” of the alarm in order
to proceed as we do. Remove the screws or pins that hold the plates
together in the vicinity of the escapement, leaving the others, though
if screws they may be loosened slightly; pry up the corner of the
plate over the lever to loosen one pivot of same and let it drop away
from the scape wheel sufficiently to let the wheel revolve until it is
locked by a wire or pegwood previously inserted in the train, after
which the plates can be pried apart more conveniently to permit the
lever being removed entirely, also the scape wheel and the one next
following. As nickel clocks differ in make-up, the operator must, of
course, exercise judgment as to the work in hand to accomplish this.
Have ready a straight-sided tin pail, with cover, that will hold at
least one-half gallon of gasoline and of diameter large enough to
receive the largest brass clock; remove the wire or pegwood and immerse
the clock into the fluid and allow it to run down; this will loosen
all the dirt and gummy oil and clean the clock very effectually. Let
it remain long enough for all the dirt to settle to the bottom of the
pail; then remove and wipe as dry as possible with a soft rag; by
having no binder on the spring it is permitted to uncoil to its full,
and thereby remove all gummy oil between its coils. Now peg out the
holes of the wheels removed and of the lever and that portion of our
work is complete.
Polish or burnish the pivots of wheels either in a split chuck in the
lathe, or by holding in a pin vise, resting the pivot on a filing block
(an ivory one is best), and revolving between the fingers, using a
smooth back file for burnishing, after the manner of pointing up a pin
tongue, only let the file be held flat, so as to maintain a cylindrical
pivot as nearly as possible. The scape wheel is now polished, i.
e., the teeth, with a revolving bristle wheel on a polishing lathe,
charged with kerosene oil and tripoli. This will smooth up the teeth
in fine form, especially those wheels that work into a lever with pin
pallets. Clean the scape wheel by dipping into gasoline to remove all
the oil and tripoli. The other wheel may simply be brushed in the
gasoline or dipped and then brushed dry.
We now turn our attention to the lever and closely examine the pallets
with a glass; if there are the least signs of wear upon them they must
be removed. Of the lever with pin pallets it is better to remove the
steel pins and insert new ones. See if the holes in the anchor where
they are inserted will admit a punch to drive them out from the back;
if not, open these holes with a drill until the ends of the pins are
reached. Put a hollow stump with a sufficiently large hole in the
staking tool, and by placing the pins in the stump they can be driven
out successively, being sure that the driving punch is no larger than
the pins; drive or insert into their places a couple of needles of the
proper size, and then break off at correct lengths; this completes the
job in this particular style of lever.
With the other style the job is not quite so easy; with a pair of
small round-nose pliers grasp the brass fork close up to the staff and
bend it back from the pallets till it lays parallel with the staff;
treat the counter poise of the fork in like manner; place a thin zinc
lap into the lathe, charged with flour of emery, and with the fingers
holding the pallets grind off all wheel teeth marks on both the
impulse and locking faces of the pallets. Then polish with a boxwood
lap charged with diamantine. It is surprising how speedily this can
be done if laps are at hand. The only care necessary is not to round
off the corners of the pallets, and as they are so large they can be
easily held flat against the laps with the thumb and finger as before
stated. Bend back the fork and counterpoise to their original position.
The fork must now be attended to; see that no notches are worn in the
horns of the fork by the steel impulse pin in the balance; if they
appear they must be dressed out and polished, also examine and smooth
if necessary the ends of the horns that bank against the balance staff.
These may seem small matters, but they are often what cause all the
trouble.
We now come to the balance staff and the hardened screws in which the
staff vibrates; their irregularities are often the source of much
vexation, and there is only one way to go at it and that is with a will
and determination to make it right. Examine the points of the staff
and see if they are in their normal shapes and are sharp and bright;
if so they will probably do their work. But we will suppose we have a
bad case in hand and will therefore treat it thoroughly according to
our method. We find the staff is large in diameter and the ends are
very blunt; the notch in the center has a burr on each side as hard as
glass, making an admirable cause for catching the horns of the fork in
some of the vibrations or in a certain position; also the round part of
the staff back of the notch is rough and looks as if it never had been
finished, and, in fact, it has not, for it truly appears as if half, if
not all, the nickel clocks are made to be finished by the watchmaker.
Remove the hairspring and place the staff between the jaws of your
bench vise, with the jaws close up to the staff, but not gripping it,
the balance “hub” resting on the jaws with the impulse pin also down
between the jaws. Have a block of brass about one-fourth inch square;
rest it on top of the staff, or on its pivot end, if it may so be
called, holding it with the thumb and finger of the left hand. Strike
this block with a hammer and drive out the staff; a hollow punch is apt
to be split in doing this, and as the pivot is to be re-pointed no harm
will be done to the pivot or to the end of the staff. Draw the temper
so it will work easily, insert into a split chuck and turn up new
points; have them long and tapering, that is, turn the points to a long
slant from the end of the staff to the body of same, or at least twice
as much taper as they generally have; polish off the back of the notch
or round part of the staff with an oil stone slip. Remove from the
chuck, smear all over with powdered boracic acid by first wetting the
staff in water, and then heat to a bright red and plunge straight into
water; it will now be white and hard; draw the temper from the staff
in the vicinity of the notch, leaving the pivot points hard as before;
re-insert into the chuck and with diamantine polish the points and
also around the staff in the vicinity of the notch. The drawing of the
temper from the center of the staff to a spring temper is to make it
less liable to breakage while driving on the balance. Fasten the staff
tight in the vise and with a rather stout brass tube, large enough
to step over the largest staff, drive on the balance to its former
position.
If the workman has a pivot polisher with a large lap, the job may be
done, without softening the staff or removing the balance, by grinding
the pivots. In turning the staff we often find it almost impossible to
hold true. We straighten the best we can and then turn up our pivots,
and as long as the untruth of the staff will not cause the balance to
wabble to such an extent as to give us a headache or cause us to look
cross-eyed it will do. We do not wish to be misunderstood or to give
the impression that we go on the principle of “good enough”; but as
gold dollars cannot be bought for seventy-five cents, neither can a
workman devote the time to have everything perfect for fifty cents; and
for this very reason do they come in such an unfinished state from the
manufacturers.
Next see if the two screws in which the balance vibrates have properly
cut countersinks; if rough or irregular, better at once draw the
temper, re-drill with a sharp-angled drill and again harden.
Occasionally a bunch of these clocks will come in with both pivots and
cones badly rusted. This has generally been caused by acid pickling,
or some sort of chemical hardening at the factory; the acid or alkali
gets into the pores of the steel and comes out after the clock has
been shipped. They are generally made in such quantities that fifty
or a hundred thousand of them have been distributed before finding out
that they were not right and then it is a matter of two or three years
before the factory hears the last of it. The trouble is attributed
to bad oil, or to anything else but the hardening, which is the real
cause, and the expense of taking back and refitting the balance
arbors and cones, paying freight both ways and standing the abuse of
disgruntled jewelers, goes on until life becomes anything but a bed of
roses. Every jeweler should warn the factory immediately on finding
rust in the cones of a shipment of new clocks and not attempt to fix
them himself, as such a fault cannot be discovered at the factory and
every day it continues means more thousands of clocks distributed that
will give trouble.
Our clock is now ready to be put together. Wind up the spring and
slip on the binder; then put in the wheels and lever; then adjust
the balance and hairspring to their proper places, slightly wind the
mainspring and then see (by bringing either horn against the staff)
whether it sticks and holds the balance; if so, shorten the fork
slightly by bending; try this until the balance and fork act perfectly
free and safe. Slightly oil the balance pivots; an excess will only
gather dust and prove detrimental, as the countersinks form an
admirable place for holding the dust. Now oil the remaining parts and
we are sadly mistaken if our clock does not make a motion that will be
gratifying.
The foregoing process may seem tedious and uncalled for and too close
mention made of the lesser portions of the work, but we must not
“despise the day of small things,” and as we are watchmakers, we are
expected to do this work, even though troublesome and the pay small; we
should also bear in mind that if we only make a nickel clock run and
keep fair time, it will be a large advertisement, and possibly repay
tenfold. It takes only an hour to do this job complete, while in many
cases only the balance staff needs attention.
Sometimes such a clock will be apparently all right mechanically but
will continue to lose time; then it is probable that the balance does
not make the proper number of vibrations, which causes the clock to
lose time. There is one way to tell this, which will soon locate the
trouble: count the train to ascertain the number of vibrations the
balance should make in one minute. You do this by counting the number
of teeth in the center wheel, which we will say is 48; third wheel
48; fourth wheel, 45; escape, 15. Multiply all teeth together, which
give us 48 × 48 × 45 × 15 = 1,555,200. Now count the leaves in the
third wheel pinion, which is 6; fourth, 6; escape, 6. Multiply these
together, 6 × 6 × 6 = 216; now divide the leaves into the teeth,
1,555,200 ÷ 216 = 7,200, which is the number of whole vibrations some
Ansonia alarm clocks make in one hour. Dividing 7,200 by 60 gives us
120, the number of vibrations per minute. Now the balance must make 120
vibrations in one minute, counting the balance going one way. If the
balance only vibrates 118, the clock will lose time and the hairspring
must be taken up or made shorter, until it makes the required number
of vibrations. If it should vibrate 122 the clock would gain and the
hairspring should be let out.
Find out the number of vibrations your balance should make and work
accordingly; and if you find that the balance makes the proper number
of vibrations in one minute, then the trouble must lie in the center
post, which has not enough friction to carry the hands and dial wheels,
or the wheel that gears into the hour wheel and regulates the alarm
hand is too tight and holds back the hands. You should find some
trouble about these wheels or center post, for where a balance makes
the proper number of vibrations in one minute, the minute hand cannot
help going around if everything else is correct.
Fig. 62 illustrates the escapement of the Western Clock Manufacturing
Company for their cheap levers. It has hardened steel pallets placed
in a mould and the fork cast around them, thus insuring exact placing
of the pallets, and the company claim that they thus secure a detached
lever escapement with all the advantages of hardened and polished
pallets at a minimum cost.
[Illustration: Fig. 62.]
Mr. F. Dauphin, of Cassel, Germany, on page 387 of Der Deutsche
Uhrmacher Zeitung, 1905, has described a serious fault of some of the
cheap American alarm clocks in the depthings of the escapements and
how he remedied it by changing the position of the pins. It is to be
regretted that Mr. Dauphin did not state the measurements of the parts
as nearly as possible in this article and also give the manufacturer’s
name, simply to enable others not as skilled as he is to do what I
would do in such a case; namely, to return it to the jobber and get a
new and correct movement in its stead _free of charge_. The American
clock manufacturers are very liberal in this respect and never hesitate
to take back a movement that was not correct when it left the factory,
even when the customer, in the attempt to correct it, has spoiled it;
spoiled or not, it goes to the waste pile anyway, when it reaches the
factory. I seriously doubt the ability of the average watch repairer to
correctly change the position of the pins as suggested; and to change
the center of action of the lever is certainly a desperate job. I
herewith give a correct drawing of an escape wheel and lever, such as
are used in the above cited clocks, made from measurements of the parts
of a clock. The drawing is, of course, enlarged. The measurements are:
Escape wheel, actual diameter, 18.11 mm.; original diameter, 17 mm.;
lever, from pin to pin, outside, 9.3 mm.; distance of centers of wheel
and lever, 10.0 mm. I found that all these measurements almost exactly
agree with Grossmann’s tables, and I do not doubt at all that they were
taken from them. There is only one mistake visible, which is in the
shape of the escape teeth, and I fail to see why this was overlooked by
those in charge at the factory; _the draw is insufficient_. It is only
from seven to eight degrees, when it should be fifteen degrees. I show
this at tooth A, in the drawing, where you can see both dotted lines,
measuring the angle of draw; line C as it is and line B as it should be.
[Illustration: Fig. 63.]
Notwithstanding the deficient draw, this escapement will work safely
as long as the pivot holes are not too large, or worn sideways; but if
you want to make it safe you should file the locking faces of teeth
slightly under; even if you do not make a model job, you have remedied
the fault. Make a disk of 18.11 mm. diameter, put it on the arbor of
the wheel and lay a straight edge from the point of the tooth to the
center of the disk, so as to see how much it needs to be filed away.
Even if this undercutting is not very true it will go.
TO MEASURE WHEELS WITH ODD NUMBERS OF TEETH.—This is a job that so
frequently comes to the watchmaker who has to replace wheels or pinions
that the following simple method should be generally appreciated. It
depends upon the fact that the radius of a circle, R, Fig. 64, equals
the versed sine E (dotted) plus the cosine B. If we stand such a wheel
on the points of the teeth, A C, and measure it we shall get the
length of the line T B only, when what we really need is the length
of the lines T B E, to give us the real diameter for our wheel, and E
we find has been cut away, so that we cannot measure it. Say it is a
15-tooth escape wheel, then by standing the old wheel up on the anvil
of a vertical micrometer, resting it on two of its teeth, as shown in
Fig. 64, the measuring screw can be brought in contact with the tooth
diametrically opposite the space between the two teeth on the anvil,
and a measurement taken, which will be less than the full diameter by
the versed sine of 12 degrees (half the angle included between two
adjoining teeth). By bringing each tooth in succession to the top, such
a wheel could be measured in fifteen different directions, which would
vary slightly, owing to the fact that some of the teeth may be bent a
little, but the mean of these measures should be what the wheel would
measure were the teeth in their original shape. If a tooth was badly
bent the three measures in which it was involved could be rejected,
and the mean of the other twelve measures taken as the correct value
and found to be, we will say, 0.732 inch. Consulting a table of
natural sines the cosine of 12 degrees is found to be 0.97815, which
subtracted from 1 gives 0.02185 as the versed sine. Multiplying this
by 0.36 inch (practically one-half of our measured 0.732) to get the
approximate radius of the wheel, we get 0.008 inch, the amount to be
added to the micrometer measurement in order to get the diameter of the
blank.
At first sight it may appear like a vicious principle that we must
know the radius of the wheel before we can determine the value of
the correction in question, but we only need to know the radius
approximately in order to determine the correction very closely, an
error of ¹/₂₀ inch in the assumed value of the radius producing an
error of only 0.001 inch in the value of the correction.
[Illustration: Fig. 64. Getting the full diameter.]
This method can of course be applied to all wheels and pinions to get
the size of the blank; with other wheels than escape wheels, where the
pitch line and the full diameter do not coincide, the addendum may be
subtracted from the full diameter to get the pitch line.
CUTTERS FOR CLOCK TRAINS.—In cutting escape wheels or others with wide
space between the teeth, it is a matter of some difficulty with many
people to enable them to set the cutter properly.
Mr. E. A. Sweet calls attention to the fact that if a cutter be set so
that its center touches the circumference of the wheel to be cut, said
cutter will be in the proper position for work. For instance, if an
escape wheel is to be cut, it is sufficient to set the cutter in such
a manner that that portion of the cutter forming the bottom of the cut
touch the circumference of the blank at the center of the cutter. It
may then be backed off and fed in with the certainty of being properly
placed.