REGULATIONS, SUSPENSIONS, CRUTCHES AND MINOR POINTS.
REGULATION.—The reader will have noticed that in describing the various
forms of seconds pendulums we have specified either eighteen or
thirty-six threads to the inch; this is because a revolution of the nut
with such a thread gives us a definite proportion of the length of the
rod, so that it means an even number of seconds in twenty-four hours.
Moving the bob up or down ¹/₁₈ inch makes the clock having a
seconds pendulum gain or lose in twenty-four hours one minute,
hence the selecting definite numbers of threads has for its reason
a philosophical standpoint, and is not a matter of convenience and
chance, as seems to be the practice with many clockmakers. With a screw
of eighteen threads, we shall get one minute change of the clock’s
rate in twenty-four hours for every turn of the nut, and if the nut is
divided into sixty parts at its edge, each of these divisions will make
a change of the clock’s rate of one second in twenty-four hours. Thus
by using a thread having a definite relation to the length of the rod
regulating is made comparatively easy, and a clock can be brought to
time without delay. Suppose, after comparing your clock for three or
four days with some standard, you find it gains twelve seconds per day,
then, turning the nut down twelve divisions will bring the rate down
to within one second a day in one operation, if the screw is eighteen
threads. With the screw thirty-six threads the nut will require moving
just the same number of divisions, only the divisions are twice as long
as those with the screw of eighteen threads.
The next thing is the size and weight of the nut. If it is to be
placed in the middle of the bob as in Figs. 10, 12 and 15, it should
project slightly beyond the surface and its diameter will be governed
by the thickness of the bob. If it is an internal nut, worked by means
of a sleeve and disc, as in Fig. 9, the disc should be of sufficient
diameter to make the divisions long enough to be easily read. If the
nut is of the class shown in Fig. 5, 6, 7, a nut is most convenient, 1
inch in diameter, and cut on its edge into thirty equal divisions, each
of which is equal to one second in change of rate in twenty-four hours,
if the screw has thirty-six threads to the inch. This gives 3.1416
inches of circumference for the thirty divisions, which makes them long
enough to be subdivided if we choose, each division being a little over
one-tenth of an inch in length, so that quarter-seconds may be measured
or estimated.
With some pendulums, Fig. 13, the bob rotates on the rod, and is in
the form of a cylinder, say 8½ inches long by 2½ inches in diameter,
and the bob then acts on its rod as the nut does, and moves up and
down when turned, and in this form of bob the divisions are cut on the
outside edge of the cover of the bob, and are so long that each one is
subdivided into five or ten smaller divisions, each altering the clock
.2 or .1 second per day.
On the top of the bob turn two deep lines, close to the edge, about
⅛-inch apart, and divide the whole diameter into thirty equal
divisions, and subdivide each of the thirty into five, and this will
give seconds and fifths of seconds for twenty-four hours. Each even
seconds division should be marked heavier than the fraction, and should
be marked from one to thirty with figures. Just above the cover on the
rod should slide a short tube, friction-tight, and to this a light
index or hand should be fastened, the point of which just reaches the
seconds circle on the bob cover, and thus indicates the division, its
number and fraction. The tube slides on the rod because the exact
place of the hand cannot be settled until it has been settled by
experiment. After this it can be fastened permanently, if thought best,
though as described it will be all sufficient. While the bob is being
raised or lowered to bring the clock to its rate, the bob might get too
far away or too near to the index and necessitate its being shifted,
and if friction-tight this can be readily accomplished, and the hand
be brought to just coincide with the divisions and look well and be a
means of accomplishing very accurate minute adjustments.
SUSPENSIONS.—Suspensions are of four kinds, cord, wire loop, knife
edges and springs. Cords are generally of loosely twisted silk and
are seldom found except in the older clocks of French or Swiss
construction. They have been entirely displaced in the later makes of
European manufactures by a double wire loop, in which the pendulum
swings from a central eye in the loop, while the loop rocks upon a
round stud by means of an eye at each end of the loop. The eyes should
all be in planes parallel to the plane of oscillation of the pendulum,
otherwise the bob will take an elliptical path instead of oscillating
in a plane. They should also be large enough to roll without friction
upon the stud and center of the loop, as any slipping or sliding of
either will cause them to soon wear out, besides affecting the rate
of the pendulum. Properly constructed loops will give practically no
friction and make a very free suspension that will last as long as the
clock is capable of keeping time, although it seems to be a very weak
and flimsy method of construction at first sight. Care should be taken
in such cases to keep the bob from turning when regulating the clock,
or the effect upon the pendulum will be the same as if the eyes were
not parallel.
Knife edge suspensions are also rare now, having been displaced by
the spring, as it was found the vibrations were too free and any
change in power introduced a circular error (See Fig. 4) by making the
long swings in longer time. They are still to be found, however, and
in repairing clocks containing them the following points should be
observed: The upper surface of the stud on which the pendulum swings
should carry the knife edge at its highest point, exactly central
with the line of centers of the stud, so that when the pendulum hangs
at rest the stud shall taper equally on both sides of the center,
thus giving equal freedom to both sides of the swing. Care should be
taken that the stud is firmly fixed, with the knife edge exactly at
right angles to the movement, and also to the back of the case. The
suspension stud and the block on the rod should be long enough to hold
the pendulum firmly in line, as the angle in the top of the rod must be
the sole means of keeping the pendulum swinging in plane. The student
will also perceive the necessity of making the angle occupy the proper
position on the rod, especially if the latter be flat. In repairing
this suspension it is usual to make the plate, fasten it in place and
then drill and file out the hole, as it is easier to get the angles
exactly in this way than to complete the plate and then attempt to
fasten it in the exact position in which it should be. After fastening
the plates in position on the rod, two holes should be drilled, a small
one at the apex of the angle (which must be exactly square and true
with the rod), and a larger one below it large enough to pass the files
easily. The larger hole can then be enlarged to the proper size, filing
the angle at the top in such a way that the small hole first drilled
forms the groove at the apex of the angle in which the knife edge of
the stud shall work when it is completed. Knife edge suspensions are
unfitted for heavy pendulums, as the weight causes the knife edge to
work into the groove and cut it, even if the latter be jeweled. Both
the edge and groove should be hardened and polished.
PENDULUM SUSPENSION SPRINGS.—Next in importance to the pendulum is
its suspension spring. This spring should be just stiff enough to make
the pendulum swing in all its vibrations in the same time; that is,
if the pendulum at one time swung at the bottom of the jar 1¼ inch
each side of the center, and at another time it swung only 1 inch each
side, that the two should be made in exactly one second. The suspension
springs are a point in the construction of a fine pendulum, that there
has been very much theorizing on, but the experiments have never thus
far exactly corroborated the theories and there are no definite rules
to go by, but every maker holds to that plan and construction that
gives his particular works the best results. A spring of sufficient
strength to materially influence the swing of the pendulum is of
course bad, as it necessitates more power to give the pendulum its
proper motion and hence there is unnecessary wear on the pallets and
escape wheel teeth, and too weak a spring is also bad, as it would not
correct any inequalities in the time of swing and would in time break
from overloading, as its granular structure would finally change,
and rupture of the spring would follow. The office of a spring is to
sustain the weight without detriment to strength and elasticity, and
if so proportioned to the weight as to be just right, it will make
the long and short swings of the pendulum of equal duration. When a
pendulum hung by a cord or knife edge instead of a spring is regulated
to mean time and swings just two inches at the bottom, any change
in the power that swings the pendulum will increase its movement or
decrease it, and in either case the rate will change, but with a proper
spring the rate will be constant under like conditions. The action of
the spring is this: In the long swings the spring, as it bends, lifts
the pendulum bob up a little more than the arc of the normal circle in
which it swings, and consequently when the bob descends, in going to
the center of its swing, it falls a little quicker than it does when
held by a cord, and this extra quick drop can be made to neutralize the
extra time taken by the bob in making extra long swings. See Fig. 4.
This action is the isochronal action of the spring, the same that is
attained in isochronal hair springs in watches.
As with the hairspring, it is quite necessary that the pendulum spring
be accurately adjusted to isochronism and my advice to every jeweler
is to thoroughly test his regulator, which can easily be done by
changing the weight or motive power. If the test should prove the lack
of isochronism he can adjust it by following these simple rules. Fig.
16 is the pendulum spring or leaf. If the short arcs should prove the
slowest, make the spring a trifle thinner at B; if fastest, reduce the
thickness of the spring at A. Continue the test until the long and
short arcs are equal. In doing this care must be taken to thin each
spring equally, if it is a double spring, and each edge equally, if
a single spring, as if one side be left thicker than the other the
pendulum will wabble.
[Illustration: Fig. 16.]
The cause of a pendulum wobbling is that there must be something wrong
with the suspension spring, or the bridge that holds the spring. If
the suspension spring is bent or kinked, the pendulum will wabble; or
if the spring should be of an unequal thickness it will have the same
effect on the pendulum; but the main cause of the pendulum wobbling in
American clocks is that the slot in the bridge that holds the spring,
or the slot in the slide that works up and down on the spring (which
is used to regulate the clock) is not parallel. When this slot is not
parallel it pinches the spring, front or back, and allows it to vibrate
more where it is the freest, causing the pendulum to wabble. We have
found that by making these slots parallel the wobbling of the pendulum
has ceased in most all cases. If the pallet staff is not at right
angles to the crutch, wobbling may be caused by the oblique action of
the crutch. This often happens when the movement is not set square in
the case.
It occasionally happens in mantel clocks that the pendulum when brought
to time is just too long for the case when too thick a spring is used.
In such a case thinning the spring will require the bob to be raised a
little and also give a better motion. If compelled to make a spring use
a piece of mainspring about .007 thick and ⅜ wide for small pendulums
and the same spring doubled for heavier pendulums, making the acting
part of the spring about 1.5 inches long.
The suspension spring for a rather heavy pendulum is better divided,
that is, two springs, held by two sets of clamps, and jointly acting as
one spring. The length will be the same as to the acting part, and that
part held at each end by the clamps may be ¾ inch long; total length,
1.5 inches with ⅜ inch at each end held in the clamps. These clamps are
best soldered on to the spring with very low flowing solder so as not
to draw the temper of the spring, and then two rivets put through the
whole, near the lower edge of the clamps. The object of securing the
clamps so firmly is so that the spring may not bend beyond the edge of
the clamps, as if this should take place the clock will be thrown off
of its rate. After a time the rate would settle and become steady, but
it only causes an extra period of regulating that does not occur when
the clamps hold the spring immovable at this point. About in the center
of each of the clamps, when soldered and riveted, is to be a hole bored
for a pin, which pins the clamp into the bracket and holds the weight
of the pendulum.
The width of this compound spring for a seconds’ pendulum of average
weight may be .60 inch, from outside to outside, each spring .15 inch
wide. This will separate the springs .30 inch in the center. With this
form of spring, the lower end of each spring being held in a pair of
clamps, the clamps will have to be let into the top of the rod, and
held in by a stout pin, or the pendulum finished with a hook which will
fit the clamp. In letting the clamp into the rod, the clamp should just
go into the mortise and be without side shake, but tilt each way from
the center a little on the pin, so that when the pendulum is hung it
may hang perpendicular, directly in the center of both springs. Also,
the top pair of clamps should fit into a bracket without shake, and
tilt a little on a pin, the same as the lower clamps. These two points,
each moving a little, helps to take any side twist away, and allows
the whole mechanism to swing in line with the center of gravity of the
mass from end to end. With the parts well made, as described, the bob
will swing in a straight line from side to side, and its path will be
without any other motion except the one of slight curvature, due to
being suspended by a fixed point at the upper clamp.
PENDULUM SUPPORTS.—Stability in the movement and in the suspension of
the pendulum is very necessary in all forms of clocks for accurate
timekeeping. The pendulum should be hung on a bracket attached to
the back of the case (see Fig. 6), and not be subject to disturbance
when the movement is cleaned. Also the movement should rest on two
brackets attached to the bracket holding the pendulum and the whole be
very firmly secured to the back board of the case. Screws should go
through the foot pieces of the brackets and into a stone or brick wall
and be very firmly held against the wall just back of the brackets.
Any instability in this part of a clock is very productive of poor
rates. The bracket, to be in its best form, is made of cast iron, with
a large foot carrying all three separate brackets, well screwed to a
strong back board and the whole secured to the masonry by bolts. Too
much firmness cannot be attained, as a lack of it is a very great
fault, and many a good clock is a very poor timekeeper, due to a lack
of firmness in its supports and fastenings. The late Edward Howard
used to make his astronomical clocks with a heavy cast iron back, to
which the rest of the case was screwed, so that the pendulum should
not swing the case. Any external influence that vibrates a wall or
foundation on which a clock is placed, is a disturbing influence, but
an instability in a clock’s attachment to such supports is a greater
one. Many pendulums swing the case in which they hang (from unstable
setting up) and never get down to or maintain a satisfactory rate from
that cause. This is also aggravated by the habit of placing grandfather
clocks on stair landings or other places subject to jarring. The writer
knows of several clocks which, after being cleaned, kept stopping
until raised off the floor and bolted to the wall, when they at once
took an excellent rate. The appearance of resting on the floor may be
preserved, if desirable, by raising the clock only half an inch or so,
just enough to free it from the floor.
CRUTCHES.—The impulse is transmitted to the pendulum from the pallet
staff by means of a wire, or slender rod, fastened at its upper end
to the pallet staff and having its lower end terminating in a fork
(crutch), loop, or bent at right angles so as to work freely in a slot
in the rod. It is also called the verge wire, owing to the fact that
older writers and many of the older workmen called the pallet fork the
verge, thus continuing the older nomenclature, although of necessity
the verge disappeared when the crown wheel was discarded.
In order to avoid friction at this very important point, the centers
of both axes of oscillation, that of the pallet arbor and that of the
pendulum spring, where it bends, should be in a straight horizontal
line. If, for instance, the center of suspension of the pendulum be
higher, then the fork and the pendulum describe two different arcs of
circles; that of the pendulum will be greater than that of the fork
at their meeting point. If, however, the center of suspension of the
pendulum be lower than that of the fork, they will also describe two
different arcs, and that of the pendulum will be smaller than that of
the fork at their point of meeting. This, as can be readily understood,
will cause friction in the fork, the pendulum going up and down in it.
This is prevented when, as stated before, the center of suspension
of the pendulum is in the prolonged straight imaginary line going
through the center of the pivots of the fork, which will cause the
arcs described by the fork and the pendulum to be the same. It will be
well understood from the foregoing that the pendulum should neither be
suspended higher nor lower, nor to the left, nor to the right of the
fork.
If the centers of motion do not coincide, as is often the case with
cheap clocks with recoil escapements, any roughness of the pendulum
rod where it slides on the crutch will stop the clock, and repairers
should always see to it that this point is made as smooth as possible
and be very slightly oiled when setting up. If putting in a new verge
wire, the workman can always tell where to bend it to form the loop by
noticing where the rod is worn and forming the loop so that it will
reach the center of that old crutch or loop mark on the pendulum rod.
If the verge wire is too long, it will give too great an arc to the
pendulum if the latter is hung below the pallet arbor, as is generally
the case with recoil escapements of the cheap clocks, and if it is too
short there will not be sufficient power applied to the pendulum when
the clock gets dirty and the oil dries, in which case the clock will
stop before the spring runs down.
An important thing to look after when repairing is in the verge wire
and loop (the slot the pendulum rod goes through). After the clock is
set up and oiled, put it on a level shelf; have a special adjusted
shelf for this level adjusting, one that is absolutely correct. Have
the dial off. If the beat is off on one side, so that it bangs up
heavily on one side of the escape wheel, bend the verge wire the
same way. That will reverse the action and put it in beat. So far so
good—but don’t stop now. Just notice whether if that shelf were tipped
forward or back, as perhaps your customer’s may, that the pendulum
should still hang plumb and free. Now if the top of your clock tips
forward, the pendulum ball inclines to hang out toward the front. We
will suppose you put two small wedges under the back of the case. Now
notice in its hanging out whether the pendulum rod pinches or bears in
the throat of the verge; or if it tips back, see if the rod hits the
other end of the slot. This verge slot should be long enough, with the
rod hanging in the middle when adjusted to beat on a level, to admit of
the clock pitching forward or back a little without creating a friction
on the ends of the slot. This little loop should be open just enough
to be nice and free; if open too much, you will notice the pallet fork
will make a little jump when carrying the ball over by hand. This is
lost motion. If this little bend of wire is not parallel it may be
opened enough inside, but if pitched forward a little it will bind in
the narrowest part of the V and then the clock will stop. The clock
beat and the tipping out or in of the clock case, causing a binding or
bearing of the pendulum rod in this verge throat, does more towards
stopping clocks just repaired than all other causes.
PUTTING IN BEAT.—To put a clock in beat, hang the clock in such a
position that when the pendulum is at rest one tooth of the escape
wheel will rest on the center of a pallet stone. Screwed on the case
of the clock at the bottom of the pendulum there is, or should be, an
index marked with degrees. Now, while the escape wheel tooth is resting
on the pallet, as explained above, the index of the pendulum should
point to zero on the index. Move the pendulum until the tooth just
escapes and note how many degrees beyond zero the pendulum point is.
Say it escapes 2° to the left; now move the pendulum until the next
tooth escapes—it should escape 2° to the right. But let us suppose it
does not escape until the index of the pendulum registers 5° to the
right of zero. In this case the rod attached to the pallets must be
bent until the escape wheel teeth escape when the pendulum is moved an
even number of degrees to the right and left of zero, when the clock
will be in beat.
CLOSE RATING WITH SHOT.—Very close rating of a seconds’ pendulum,
accompanied by records in the book, may be got with the nut alone, but
there is the inconvenience of stopping the clock to make an alteration.
This may be avoided by having a small cup the size of a thimble or
small pill box on the pendulum top. This can be lifted off and put back
without disturbing the motion of the pendulum. In using it a number of
small shot, selected of equal size, are put in, say 60, and the clock
brought as nearly as possible to time by the nut. After a few days
the cup may be emptied and put back, when on further trial the value
of the 60 shot in seconds a day will be found. This value divided by
60 will give the value of a single shot, by knowing which very small
alterations of rate may be made with a definite approach towards
accuracy, and in much less time than by putting in or taking out one or
more shot at random.