SPRINGS, WEIGHTS AND POWER.
We see by the preceding calculations that there is one definite point
in the time train of a clock; the center arbor, which carries the
minute hand, must revolve once in one hour; from this point we may
vary the train both ways, toward the escape wheel to suit the length
of pendulum which we desire to use, and toward the barrel to suit the
length of time we want the clock to run. The center arbor is therefore
generally used as the point at which to begin calculations, and it
is also for this reason that the number of teeth in the center wheel
is the starting point in train calculations toward the escape wheel,
while the center pinion is the starting point in calculations of the
length of time the weight or spring is to drive the clock. Most writers
on horology ignore this point, because it seems self-evident, but its
omission has been the cause of much mystification to so many students
that it is better to state it in plain terms, so that even temporary
confusion may be avoided.
Sometimes there is a second fixed point in a time train; this occurs
only when there is a seconds hand to be provided for; when this is
the case the seconds hand must revolve once every minute. If it is a
seconds pendulum the hand is generally carried on the escape wheel and
the relation of revolutions between the hour and seconds wheels must
then be as one is to sixty. This might be accomplished with a single
wheel having sixty times as many teeth as the pinion on the seconds
arbor; but the wheel would take up so much room, on account of its
large circumference, that the movement would become unwieldy because
there would be no room left for the other wheels; so it is cheaper to
make more wheels and pinions and thereby get a smaller clock. Now the
best practical method of dividing this motion is by giving the wheels
and pinions a relative velocity of seven and a half and eight, because
7.5 × 8 = 60.
Thus if the center wheel has 80 teeth, gearing into a pinion of 10, the
pinion will be driven eight times for each revolution of the center
wheel, while the third wheel, with 75 teeth, will drive its pinion of
10 leaves 7.5 times, so that this arbor will go 7.5 times eight, or 60
times as fast as the center wheel.
If the clock has no seconds hand this second fixed point is not present
in the calculations and other considerations may then govern. These
are generally the securing of an even motion, with teeth of wheels
and pinions properly meshing into each other, without incurring undue
expense in manufacture by making too many teeth in the pinions and
consequently in the wheels. For these reasons pinions of less than
seven or more than ten leaves are rarely used in the common clocks,
although regulators and fine clocks, where the depthing is important,
frequently have 12, 14 or 16 leaves in the pinions, as is also the case
with tower clocks, where the increased size of the movement is not
as important as a smoothly running train. Clocks without pendulums,
carriage clocks, locomotive levers and nickel alarms, also have
different trains, many of which have the six leaf pinion, with its
attendant evils, in their trains.
WEIGHTS.--Weights have the great advantage of driving a train with
uniform power, which a spring does not accomplish: They are therefore
always used where exactness of time is of more importance than
compactness or portability of the clock. In making calculations for a
weight movement, the first consideration is that as the coils of the
cord must be side by side upon the barrel and each takes up a definite
amount of space, a thicker movement (with longer arbors) will be
necessary, as the barrel must give a sufficient number of turns of the
cord to run the clock the desired time and the length of the barrel,
with the wheel and maintaining power all mounted upon the one arbor,
will determine the thickness of the movement. If the clock is to have
striking trains their barrels will generally be of more turns and
consequently longer than the time barrel and in that case the distance
between the plates is governed by the length of the longest barrel and
its mechanism.
The center wheel, upon the arbor of which sits the canon pinion with
the minute hand, must, since the hand has to accomplish its revolution
in one hour, also revolve once in an hour. When, therefore, the pinion
of the center arbor has 8 leaves and the barrel wheel 144, then the
8 pinion leaves, which makes one revolution per hour, would require
the advancing of 8 teeth of the barrel wheel, which is equal to the
eighteenth part of its circumference. But when the eighteenth part
in its advancing consumes 1 hour, then the entire barrel wheel will
consume 18 hours to accomplish one revolution. If, now, 10 coils of
the weight cord were laid around the barrel, the clock would then run
10 × 18 = 180 hours, or 7½ days, before it is run down.
Referring to what was said in a previous chapter on wheels being merely
compound levers, it will be seen that as we gain motion we lose power
in the same ratio. We shall also see that by working the rule backwards
we may arrive at the amount of force exerted on the pendulum by the
pallets. If we multiply the circumference of the escape wheel in inches
by the number of its revolutions in one hour we will get the number of
inches of motion the escape wheel has in one hour. Now if we multiply
the weight by the distance the barrel wheel travels in one hour and
divide by the first number we shall have the force exerted on the
escape wheel. It will be simpler to turn the weight into grains before
starting, as the division is less cumbersome.
Another way is to find how many times the escape wheel revolves to one
turn of the barrel and divide the weight by that number, which will
give the proportion of weight at the escape wheel, or rather would do
so if there were no power lost by friction. It is usual to estimate
that three-quarters of the power is used up in frictions of teeth and
pivots, so that the amount actually used for propulsion of the pendulum
is very small, being merely sufficient to overcome the bending moment
of the suspension spring and the resistance of the air.
It is for this reason that clocks with finely cut trains and jeweled
pivots, thus having little train friction, will run with very small
weights. The writer knows of a Howard regulator with jeweled pivots
and pallets running a 14-pound pendulum with a five-ounce driving
weight. Of course this is an extreme instance and was the result of an
experiment by an expert watchmaker who wanted to see what he could do
in this direction.
Usually the method adopted to determine the amount of weight that is
necessary for a movement is to hang a small tin pail on the weight
cord and fill it with shot sufficient to barely make the clock keep
time. When this point has been determined, then weigh the pail of shot
and make your driving weight from eight to sixteen ounces heavier. In
doing this be sure the clock is in beat and that it is the lack of
power which stops the clock; the latter point can be readily determined
by adding or taking out shot from the pail until the amount of weight
is determined. The extra weight is then added as a reserve power, to
counteract the increase of friction produced by the thickening of the
oil.
Many clock barrels have spiral grooves turned in them to assist in
keeping the coils from riding on each other, as where such riding
occurs the riding coils are farther from the center of the barrel
than the others, which gives them a longer leverage and greater power
while they are unwinding, so that the power thus becomes irregular and
affects the rate of the clock, slowing it if the escapement is dead
beat and making it go faster if it is a recoil escapement.
Clock cords should be attached to the barrel at the end which is the
farthest from the pendulum, so that as they unwind the weight is
carried away from the pendulum. This is done to avoid sympathetic
vibrations of the weight as it passes the pendulum, which interfere
with the timekeeping when they occur. If the weight cannot be brought
far enough away to avoid vibrations a sheet of glass may be drilled
at its four corners and fixed with screws to posts placed in the back
of the case at the point where vibration occurs, so that the glass is
between the pendulum rod and the weight, but does not interfere with
either. This looks well and cures the trouble.
We have, heretofore, been speaking of weights which hang directly from
the barrel, as was the case with the older clocks with long cases, so
that the weight had plenty of room to fall. Where the cases are too
short to allow of this method, recourse is had to hanging the weight
on a pulley and fastening one end of the cord to the seat board. This
involves doubling the amount of weight and also taking care that the
end of the cord is fastened far enough from the slot through which it
unwinds so that the cords will not twist, as they are likely to do if
they are near together and the cord has been twisted too much while
putting it on the barrel. Twisting weight cords are a frequent source
of trouble when new cords have been put on a clock. The pulley is
another source of trouble, especially if wire cords (picture cords)
or cables are used. Wire cable should not be bent in a circle smaller
than forty times its diameter if flexibility is to be maintained, hence
pulleys which were all right for gut or silk frequently prove too
small when wire is substituted and kinks, twisted and broken cables
frequently result from this cause. This is especially the case with
the heavy weight of striking trains of hall and chiming clocks, where
double pulleys are used, and also leads to trouble by jamming and
cutting the cables and dropping of the weights in tower clocks where a
new cable of larger size is used to replace an old one which has become
unsafe from rust, or cut by the sheaves.
Weight cords on the striking side of a clock should always be left long
enough so that they will not run down and stop before the time train
has stopped. This is particularly the case with the old English hall
clocks, as many of them will drop or push their gathering racks free
of the gathering pinion under such conditions and then when the clock
is wound it will go on striking continuously until the dial is taken
off and the rack replaced in mesh with the gathering pinion. As clocks
are usually wound at night, the watchmaker can see the disturbance that
would be caused in a house in the “wee sma’ hours” by such a clock
going on a rampage and striking continuously.
OILING CABLES.--Clock cables, if of wire and small in size, should be
oiled by dipping in vaseline thinned with benzine of good quality.
Both benzine and vaseline must be free from acid, as if the latter
is present it will attack the cable. This thinning will permit the
vaseline to permeate the entire cable and when the benzine evaporates
it will leave a thin film of vaseline over every wire, thus preventing
rust. Tower clock cables should be oiled with a good mineral oil, well
soaked into them to prevent rusting. Gut clock cords, when dry and
hard, are best treated with clock oil, but olive oil or sperm oil will
also be found good to soften and preserve them. New cords should always
be oiled until they are soft and flexible. If the weight is under ten
pounds silk cords are preferable to gut or wire as they are very soft
and flexible.
In putting on a new cable or weight cord the course of the weight and
cord should be closely watched at all points, to see that they remain
free and do not chafe or bind anywhere and also that the coils run
evenly and freely, side by side; sometimes, especially with wire, a new
cable gets kinked by riding the first time of winding and is then very
difficult to cure of this serious fault. Another point to watch is to
see that the position of the cord when wound up will not cause an end
thrust upon the barrel, which will interfere with the timekeeping if it
is overwound, so that the weight is jammed against the seatboard; this
frequently happens with careless winding, if there is no stop work.
To determine the lengths of clock cords or weights, we may have to
approach the question from either end. If the clock be brought in
without the cords, we first count the number of turns we can get on
the barrel. This may be done by measuring the length of the barrel and
dividing it by the thickness of the cord, if the barrel is smooth, or
by counting the grooves if it be a grooved barrel. Next we caliper the
diameter and add the thickness of one cord, which gives us the diameter
of the barrel to the center of the cords, which is the real or working
diameter. Multiply the distance so found by 3.14156, which gives the
circumference of the barrel, or the length of cord for one turn of the
barrel. Multiply the length of one turn by the number of turns and we
have the length of cord on the barrel, when it is fully wound. If the
cord is to be attached to the weight, measure the distance from the
center of barrel to the bottom of the seat board and leave enough for
tying. If the weight is on a pulley it will generally require about
twelve inches to reach from the barrel through the slot of the seat
board, through the pulley to the point of fastening.
To get the fall of the weight, stand it on the bottom of the case and
measure the distance from the top of the point of attachment to the
bottom of the seat board. This will generally allow the weight to fall
within two inches of the bottom and thus keep the cable tight when
the clock runs down; thus avoiding kinks and over-riding when we wind
again after allowing the clock to run down. If the weight has a pulley
and double cord, measure from the top of the pulley to the seatboard,
with the weight on the bottom, and then double this measurement for
the length of the cord. This measure is multiplied by as many times as
there are pulleys in the case of additional sheaves. Striking trains
are frequently run with two coils or layers of cord, on the barrel,
time trains never have but one.
Now, having the greatest available length of cord determined according
either of the above conditions, we can determine the number of turns
for which we have room on our barrel and divide the length of cord
by the number of turns. This will give us the length of one turn of
the cord on our barrel and thus having found the circumference it is
easy to find the diameter which we must give our barrel in suiting a
movement to given dimensions of the case. This is frequently done where
the factory may want a movement to fit a particular style and size of
case which has proved popular, or when a watchmaker desires to make a
movement for which he has, or will buy, a case already made.
As to tower clock cables, getting the length of cable on the barrel is,
of course, the same as given above, but the rest of it is an individual
problem in every case, as cables are led so differently and the length
of fall varies so that only the professional tower clock men are fitted
to make the measurements for new work and they require no instruction
from me. It might be well to add, however, that in the tower clocks
by far the greater part of the cable is always outside the clock and
only the inner end coils and uncoils about the barrel. It is for this
reason that the outer ends of the cables are so generally neglected by
watchmakers in charge of tower clocks and allowed to cut and rust until
they drop their weights. Caretakers of tower clocks should remember
that the inner ends of cables are always the best ends; the parts that
need watching are those in the sheaves or leading to the sheaves.
Tower clocks should have the cables marked where to stop to prevent
overwinding.
In chain drives for the weights of cuckoo and other clocks with exposed
weights, we have generally a steel sprocket wheel with convex guiding
surfaces each side of the sprocket and projecting flanges each side of
the guides; one of these flanges is generally the ratchet wheel. The
ratchet wheel, guide, sprocket, guide and flange, form a built-up wheel
which is loose on the arbor and is pinned close to the great wheel,
which is driven by a click on the wheel working into the ratchet of
the drive. It must be loose on the arbor, because the clock is wound
by pulling the sprocket and ratchet backward by means of the chain
until the weight is raised clear up to the seat board. There are no
squares on the arbors, which have ordinary pivots at both ends, and the
great wheel is fast on the arbor. The diameter of the convex portion
of the wheel each side of the sprocket is the diameter of the barrel,
and the chain should fit so that alternate links will fit nicely in
the teeth of the sprocket; where this is not the case they will miss a
link occasionally and the weight will then fall until the chain catches
again, when it will stop with a jerk; bent or jammed links in the chain
will do the same thing. Sometimes a light chain on a heavy weight
will stretch or spread the links enough to make their action faulty.
If examination shows a tendency to open the links, they should be
soldered; if they are stretching, a heavier chain of correct lengths of
links should be substituted. Twisted chains are another characteristic
fault and are usually the result of bent or jammed links. A close
examination of such a chain will generally reveal several links in
succession which are not quite flat and careful straightening of these
links will generally cure the tendency to twist.
MAINSPRINGS FOR CLOCKS.--There are many points of difference between
mainsprings for clocks and those for watches. They differ in size,
strength, number of coils and in their effect on the rates of the clock.
Watch springs are practically all for 30-hour lever escapements, with
a few cylinder, duplex and chronometer escapements. If a fusee watch
happens into a shop nowadays it is so rare as to be a curiosity worth
stopping work to look at.
The clocks range all the way from 30 hours to 400 days in length of
time between windings and include lever, cylinder, duplex, dead beat,
half dead beat, recoil and other escapements. Furthermore some of
these, even of the same form of escapements, will vary so in weight
and the consequent influence of the spring that what will pass in one
case will give a wildly erratic rate in another instance. Many of the
small French clocks have such small and light pendulums that very nice
management of the stop works is necessary to prevent the clock from
gaining wildly when wound or stopping altogether when half run down.
Nothing will cause a clock with a cylinder escapement to vary in time
more than a set or gummy mainspring, for it will gain time when first
wound and lose when half run down, or when there is but little power
on the train. In such a case examine the mainspring and see that it is
neither gummy nor set. If it is set, put in a new spring and you can
probably bring it to time.
With a clock it depends entirely on the kind of escapement that it
contains, whether it runs faster or slower, with a stronger spring;
if you put a stronger mainspring in a clock that contains a recoil
escapement the clock will gain time, because the extra power,
transmitted to the pallets will cause the pendulum to take a shorter
arc, therefore gain time, where the reverse occurs in the dead-beat
escapement. A stronger spring will cause the dead-beat pendulum to take
a longer arc and therefore lose time.
If a pendulum is short and light these effects will be much greater
than with a long and heavy pendulum.
At all clock factories they test the mainsprings for power and to see
that they unwind evenly; those that do are marked No. 1, and those that
do not are called “seconds.” The seconds are used only for the striking
side of the clocks, while the perfect ones are used for the running,
or time side. Sometimes, however, a seconds’ spring will be put on the
time side and will cause the clock to vary in a most erratic way. This
changing of springs is very often done by careless or ignorant workmen
in cleaning and then they cannot locate the trouble.
All mainsprings for both clocks and watches should be smooth and well
polished. Proper attention to this one item will save many dollars’
worth of time in examining movements to try to detect the cause of
variations.
A rough mainspring (that is, an emery finished mainspring) will lose
one-third of its power from coil friction, and in certain instances
even one-half. The deceptive feature about this to the watchmaker
is that the clock will take a good motion with a rough spring fully
found, but will fall off when partly unwound, and the consequence is
that he finds a good motion when the spring is put in and wound, and
he afterward neglects to examine the spring when he examines the rate
as faulty. The best springs are cheap enough, so that only the best
quality should be used, as it is easy for a watchmaker to lose three or
four dollars’ worth of time looking for faults in the escapement, train
and everywhere else, except the barrel, when he has inserted a rough,
thick, poorly made spring. The most that he can save on the cheaper
qualities of springs is about five cents per spring and we will ask any
watchmaker how long it would take to lose five cents in examination of
a movement to see what is defective.
Here is something which you can try yourself at the bench. Take a
rough watch mainspring; coil it small enough to be grasped in the hand
and then press on the spring evenly and steadily. You will find it
difficult to make the coils slide on one another as the inner coils get
smaller; they will stick together and give way by jerks. Now open your
hand slowly and you will feel the spring uncoiling in an abrupt, jerky
way, sometimes exerting very little pressure on the hand, at other
times a great deal. A dirty, gummy spring will do the same thing. Now
take a clean, well polished spring and try it the same way; notice how
much more even and steady is the pressure required to move the coils
upon each other, either in compressing or expanding. Now oil the well
polished spring and try it again. You will find you now have something
that is instantly responding, evenly and smoothly, to every variation
of pressure. You can also compress the spring two or three turns
farther with the same force. This is what goes on in the barrel of
every clock or watch; you have merely been using your hand as a barrel
and _feeling_ the action of the springs.
Now a well finished mainspring that is gummy is as irregular in its
action as the worst of the springs described above, yet very few
watchmakers will take out the springs of a clock if they are in a
barrel. One of them once said to me, “Why, who ever takes out springs?
I’ll bet I clean a hundred clocks before I take out the springs of one
of them!” Yet this same man had then a clock which had come back to him
and which was the cause of the conversation.
There must be in this country over 25,000 fine French clocks in
expensive marble or onyx cases, which were given as wedding presents to
their owners, and which have never run properly and in many instances
cannot be made to run by the watchmakers to whom they were taken
when they stopped. Let me give the history of one of them. It was an
eight-day French marble clock which cost $25 (wholesale) in St. Louis
and was given as a wedding present. Three months later it stopped and
was taken to a watchmaker well known to be skillful and who had a fine
run of expensive watches constantly coming to him. He cleaned the
clock, took it home and it ran three hours! It came back to him three
times; during these periods he went over the movement repeatedly; every
wheel was tested in a depthing tool and found to be round: all the
teeth were examined separately under a glass and found to be perfect;
the pinions were subjected to the same careful scrutiny; the depthings
were tried with each wheel and pinion separately; the pivots were
tested and found to be right; the movement was put in its case and
examined there; it would run all right on the watchmaker’s bench, but
not in the home of its owner. It would stop every time it was moved in
dusting the mantel. He became disgusted and took the clock to another
watchmaker, a railroad time inspector; same results. In this way the
clock moved about for three years; whenever the owner heard of a man
who was accounted more than ordinarily skillful he took him the clock
and watched him “fall down” on it. Finally it came into the hands of an
ex-president of the American Horological Society. He made it run three
weeks. When he found the clock had stopped again he refused pay for
it. Three months later he called and got the clock, kept it for three
weeks, brought it back without explanation and lo, the clock ran! It
would even run considerably out of beat! When asked what he had done to
the clock, he merely laughed and said “Wait.”
A year later the clock was still going satisfactorily and he explained.
“That was the first time I ever got anything I couldn’t fix and it made
me ashamed. I kept thinking it over. Finally one night in bed I got to
considering why a clock wouldn’t run when there was nothing the matter
with it. The only reason I could see was lack of power. Next morning I
got the clock and put in new mainsprings, the best I could find. The
clock was cured! None of these other men who had the clock took out the
springs. They came to me all gummed up, while the rest of the clock was
clean, bright and in perfect order. I cleaned the springs and returned
the clock; it ran three weeks. When I took it back I put in stronger
springs, because I found them a little soft on testing them. If any of
your friends have French clocks that won’t go, send them to me.”
Three-quarters of the trouble with French clocks is in the spring box;
mainspring too weak, gummy or set; stop works not properly adjusted,
or left off by some numskull who thought he could make the clock keep
time without it when the maker couldn’t; mainspring rough, so that
it uncoils by jerks; spring too strong, so that the small and light
pendulum cannot control it. These will account for far more cases than
the “flat wheel” story that so often comes to the front to account for
a failure on the part of the workman. Of course he must say something
to his boss to account for his failure and the “wheels out of round”
and “the faulty depthing” have been standard excuses for French clocks
for a century. Of course they do occur, but not nearly as often as they
are credited with, and even then such a clock may be made to perform
creditably if the springs are right.
Another source of trouble is buckled springs, caused by some workman
taking them out or putting them in the barrel without a mainspring
winder. There are many men who will tell you that they never use a
winder; they can put any spring in without it. Perhaps they can, but
there comes a day when they get a soft spring that is too wide for this
treatment and they stretch one side of it, or bend, or kink it, and
then comes coil friction with its attendant evils. These may not show
with a heavy pendulum, but they are certain to do so if it happens to
be an eight-day movement with light pendulum or balance, and this is
particularly true of a cylinder.
All springs should be cleaned by soaking in benzine or gasoline and
rubbing with a rag until all the gum is off them before they are
oiled. Heavy springs may be wiped by wrapping one or two turns of a
rag around them and pushing it around the coils. The spring should be
well cleaned and dried before oiling. A quick way of cleaning is to
wind the springs clear up; stick a peg in the escape wheel; remove the
pallet fork; plunge the whole movement into a pail of gasoline large
enough to cover it; let it stand until the gasoline has soaked into the
barrels; remove the peg and let the trains run down. The coils of the
spring will scrub each other in unwinding; the pivots will clean the
pivot holes and the teeth of wheels and pinions will clean each other.
Then take the clock apart for repairs. Springs which are not in barrels
should be wound up and spring clamps put on them before taking down the
clock. About six sizes of these clamps (from 2½ inches to ¾ inch) are
sufficient for ordinary work.
Rancid oil is also the cause of many “come-backs.” Workmen will buy
a large bottle of good oil and leave it standing uncorked, or in the
sun, or too near a stove in winter time, until it spoils. Used in this
condition it will dry or gum in a month or two and the clock comes
back, if the owner is particular; if not, he simply tells his friends
that you can’t fix a clock and they had better go elsewhere with their
watches.
For clock mainsprings, clock oil, such as you buy from material
dealers, is recommended provided it is intended for French mainsprings.
If the lubricant is needed for coarse American springs, mix some
vaseline with refined benzine and put it on liberally. The benzine will
dissolve the vaseline and will help to convey the lubricant all over
the spring, leaving no part untouched. The liquid will then evaporate,
leaving a thin coating of vaseline on the spring.
It is best to let springs down, with a key made for the purpose. It
is a key with a large, round, wooden handle, which fills the hand of
the watchmaker when he grasps it. Placing the key on the arbor square,
with the movement held securely in a vise, wind the spring until you
can release the click of the ratchet with a screwdriver, wire or other
tool; hold the click free of the ratchet and let the handle of the key
turn slowly round in the hand until the spring is down. Be careful not
to release the pressure on the key too much, or it will get away from
you if the spring is strong, and will damage the movement. This is why
the handle is made so large, so that you can hold a strong spring.
It is of great importance, if we wish to avoid variable coil friction,
that the spring should wind, from the very starting, concentrically;
i. e., that the coils should commence to wind in regular spirals,
equidistant from each other, around the arbor. In very many cases we
find, when we commence to wind a spring, that the innermost coil bulges
out on one side, causing, from the very beginning, a greater friction
of the coils on that side, the outer ones pressing hard against it as
you continue to wind, while on the outer side of the arbor they are
separated from each other by quite a little space between them, and
that this bulge in the first coil is overcome and becomes concentric to
the arbor only after the spring is more than half way wound up. This
necessarily produces greater and more variable coil friction. When a
spring is put into the barrel the innermost coil should come to the
center around the arbor by a gradual sweep, starting from at least one
turn around away from the other coils. Instead of that, we more often
find it laying close to the outer coils to the very end, and ending
abruptly in the curl in the soft end that is to be next the arbor. When
this is the case in a spring of uniform thickness throughout, it is
mainly due to the manner of first winding it from its straight into a
spiral form. To obviate it, I generally wind the first coils, say two
or three, on a center in the winder, a trifle smaller than the regular
one, which is to be of the same diameter of the arbor center in the
barrel. You will find that the substitution of the regular center,
afterwards, will not undo the extra bending thus produced on the inner
coils, and that the spring will abut by a more gradual sweep at the
center, and wind more concentrically.
The form of spring formerly used with a fusee in English carriage
clocks and marine chronometers is a spring tapering slightly in
thickness from the inner end for a distance of two full coils, the
thickness increasing as we move away from the end, then continuing
of uniform thickness until within about a coil and a half from the
other end, when it again increases in thickness by a gradual taper.
The increase in the thickness towards the outer end will cause it to
cling more firmly to the wall of the barrel. The best substitute for
this taper on the outside is a brace added to some of the springs
immediately back of the hole. With this brace, and the core of the
winding arbor cut spirally, excellent results are obtained with a
spring of uniform thickness throughout its entire length. Something,
too, can be done to improve the action of a spring that has no brace,
by hooking it properly to the barrel. The hole in the spring on the
outside should never be made close to the end; on the contrary, there
should be from a half to three-quarters of an inch left beyond the
hole. This end portion will act as a brace.
When the spring is down, the innermost coil of it should form a gradual
spiral curve towards the center, so as to meet the arbor without
forcing it to one side or the other. This curve can be improved upon,
if not correct, with suitably shaped pliers; or it can be approximated
by winding the innermost coils first on an arbor a little smaller in
diameter than the barrel arbor itself.
Another and very important factor in the development of the force of
the spring is the proper length and thickness of it. For any diameter
of barrel there is but one length and one thickness of spring that will
give the maximum number of turns to wind. This is conditioned by the
fact that the volume which the spring occupies when it is down must
not be greater nor less than the volume of the empty space around the
arbor into which it is to be wound, so that the outermost coil of the
spring when fully wound will occupy the same place which the innermost
occupies when it is down. In a barrel, the diameter of whose arbor
is one-third that of the barrel, the condition is fulfilled when the
measure across the coils of the spring as it lays against the wall of
the barrel, is 0.39 of the empty space, or, taking the diameter of the
barrel as a comparison, 0.123 of the latter; in other words, nearly
one-eighth of the diameter of the barrel. This is the width that will
give the greatest number of turns to wind, whatever may be the length
or thickness of any spring. If now we desire a spring to wind a given
number of turns, there is but one thickness and one length of it that
will permit it to do so. The thickness remaining the same, if we make
the spring longer or shorter, we reduce the number of turns it will
wind; more rapidly by making it shorter, less so by making it longer.
It is therefore not only useless, but detrimental, to put into a barrel
a greater number of coils, or turns, than are necessary, not only
because it will reduce the number of turns the barrel will wind, but it
will produce greater coil friction by filling up the space with more
coils than are necessary.
A mainspring in the act of uncoiling in its barrel always gives a
number of turns equal to the difference between the number of coils in
the up and the down positions. Thus, if 17 be the number of coils when
the spring is run down, and 25 the number when against the arbor, the
number of turns in uncoiling will be 8, or the difference between 17
and 25.
The cause of breakage is usually, that the inner coils are put to the
greatest strain, and then the slightest flaw in the steel, a speck of
rust, grooves cut in the edges of the spring by allowing a screwdriver
to slip over them, or an unequal effect of change of temperature,
causes the fracture, and leaves the spring free to uncoil itself with
very great rapidity.
Now this sudden uncoiling means that the whole energy of the spring is
expended on the barrel in a very small fraction of a second. In reality
the spring strikes the inner side of the rim of the barrel, a violent
blow in the direction the spring is turning, that is, backwards; this
is due to the mainspring’s inertia and its very high mean velocity.
The velocity is nothing at the outer end, where the spring is fixed,
but rises to the maximum at the point of fracture, and the kinetic
energy at various points of the spring could no doubt be calculated
mathematically or otherwise.
For instance, take a going barrel spring of eight and a half turns,
breaking close up to the center while fully wound. A point in the
spring at the fracture makes eight turns in the opposite direction
to which it was wound, a point at the middle four turns, and a point
at the outer end nothing, an effect similar to the whole mass of the
spring making four turns backwards. At its greatest velocity it is
suddenly stopped by the barrel, wheel teeth engaging its pinion; this
stoppage or collision is what breaks center pinions, third pivots,
wheel teeth, etc., unless their elasticity, or some interposed
contrivance, can safely absorb the stored-up energy of the mainspring,
the spring being, as every one knows, the heaviest moving part in an
ordinary clock, except where the barrel is exceptionally massive.
STOP WORKS.--Stop works are devices that are but little understood by
the majority of workmen in the trade. They are added to a movement for
either one or both of two distinct purposes: First, as a safety device,
to prevent injury to the escape wheel from over winding, or to prevent
undue force coming on the pendulum by jamming the weight against the
top of the seat board and causing a variation in time in a fine clock;
or, second, to use as a compromise by utilizing only the middle portion
of a long and powerful spring, which varies too much in the amount of
its power in the up and down positions to get a good rate on the clock
if all the force of the spring were utilized in driving the movement.
With weight clocks, the stop work is a safety device and should always
be set so that it will stop the winding when the barrel is filled
by the cord; consequently the way to set them is to wind until the
barrel is barely full and set the stops with the fingers locked so as
to prevent any further action of the arbor in the direction of the
winding and the cord should then be long enough to permit the weight
to be free. Then unwind until within half a coil of the knot in the
cord where it is attached to the barrel and see that the weight is also
free at the bottom of the case, when the stops again come into action.
This will allow the full capacity of the barrel to be used.
When stop work is found on a spring barrel, it may be taken for granted
that the barrel contains more spring than is being wound and unwound
in the operation of the clock and it then becomes important to know
how many coils are thus held under tension, so that we may put it back
correctly after cleaning. Wind up the spring and then let it slowly
down with the key until the stop work is locked, counting the number
of turns, and writing it down. Then hold the spring with the letting
down key and take a screw driver and remove the stop from the plate;
then count the number of turns until the spring is down and also write
that down. Then take out the spring and clean it. You may find such a
spring will give seventeen turns in the barrel without the stop work
on, while it will give but ten with the stop work; also that the arbor
turned four revolutions after you removed the stop. Then the spring ran
the clock from the fourth to the fourteenth turns and there were four
coils unused around the arbor, ten to run the clock and three unused at
the outer end around the barrel. This would indicate a short and light
pendulum or balance, which is very apt to be erratic under variations
of power, and if the rate was complained of by the customer you can
look for trouble unless the best adjustment of the spring is secured.
Put the spring back by winding the four turns and putting on the stop
work in the locked position; then wind. If the clock gains when up and
loses when down, shift the stop works half a turn backwards or forwards
and note the result, making changes of the stop until you have found
the point at which there is the least variation of power in the up and
down positions. If the variation is still too great a thinner spring
must be substituted.
There are several kinds of stop work, the most common being what is
known as the Geneva stop, a Maltese cross and a finger such as is
commonly seen on watches. For watches they have five notches, but for
clocks they are made with a greater number of notches, according to the
number of turns desired for the arbor. The finger piece is mounted on a
square on the barrel arbor and the star wheel on the stud on the plate.
In setting them see that the finger is in line with the center of the
star wheel when the stop is locked, or they will not work smoothly.
There is another kind of stopwork which is used in some American
clocks, and as there is no friction with it, and no fear of sticking,
nor any doubt of the certainty of its action, it is perhaps the most
suitable for regulators and other fine clocks which have many turns of
the barrel in winding. This stop is simple and sure. It consists of a
pair of wheels of any numbers with the ratio of odd numbers as 7 and
6, 9 and 10, 15 and 16, 30 and 32, 45 and 48, etc.; the smaller wheel
is squared on the barrel arbor and the larger mounted on a stud on the
plate. These wheels are better if made with a larger number of teeth.
On each wheel a finger is planted, projecting a little beyond the
outsides of the wheel teeth, so that when the fingers meet they will
butt securely. The meeting of these fingers cannot take place at every
revolution because of the difference in the numbers of the teeth of
the wheels; they will pass without touching every time till the cycle
of turns is completed, as one wheel goes round say sixteen times while
the other goes fifteen, and when this occurs the fingers will engage
and so stop further winding. When the clock has run down sixteen turns
of the barrel the fingers will again meet on the opposite side, and so
the barrel will be allowed to turn backwards and forwards for sixteen
revolutions, being stopped by the fingers at each extreme. When in
action the fingers may butt either at a right or an obtuse angle, only
not too obtuse, as this would put a strain on, tending to force the
wheels apart. If preferred the fingers may be made of steel, but this
is not necessary.
[Illustration: Fig. 83.]
MAINTAINING POWERS.--Astronomical clocks, watchmaker’s regulators
and tower clocks are, or at least should be, fitted with maintaining
power. A good tower clock should not vary in its rate more than five
to ten seconds a week. Many of them, when favorably situated and
carefully tended, do not vary over five to ten seconds per month. It
requires from five to thirty minutes to wind the time trains of these
clocks and the reader can easily see where the rate would go if the
power were removed from the pendulum for that length of time; hence a
maintaining power that will keep nearly the same pressure on the escape
wheel as the weight does, is a necessity. Astronomical clocks and fine
regulators have so little train friction, especially if jeweled, that
when the barrel is turned backwards in winding the friction between
the barrel head and the great wheel is sufficient to stop the train,
or even run it backwards, injuring the escape wheel and, of course,
destroying the rate of the clock; therefore they are provided with a
device that will prevent such an occurrence. Ordinary clocks do not
have the maintaining power because only the barrel arbor is reversed
in winding, and that reversal is never for more than half a turn at a
time, as the power is thrown back on the train every time the winder
lets go of the key to turn his hand over for another grip.
[Illustration: Fig. 84.]
[Illustration: Fig. 85.]
Figs. 83, 84 and 85 show the various forms of maintaining powers, which
differ only in their mechanical details. In all of them the maintaining
power consists of two ratchet wheels, two clicks and either one or
two springs; the springs vary in shape according to whether the great
wheel is provided with spokes or left with a web. If the great wheel
has spokes the springs are attached on the outside of the large ratchet
wheel so that they will press on opposite spokes of the great wheel
and are either straight, curved or coiled, according to the taste of
the maker of the clock and the amount of room. If made with a web a
circular recess is cut in the great wheel, see Fig. 83, wide and deep
enough for a single coil of spring wire which has its ends bent at
right angles to the plane of the spring and one end slipped in a hole
of the ratchet and the other in a similar hole in the recess of the
great wheel. A circular slot is cut at some portion of the recess in
the great wheel where it will not interfere with the spring and a screw
in the ratchet works back and forth in this slot, limiting the action
of the spring. Stops are also provided for the spokes of the great
wheel in the case of straight, curved or coiled springs, Figs. 84 and
85. These stops are set so as to give an angular movement of two or
three teeth of the great wheel in the case of tower clocks and from
six to eight teeth in a regulator. The springs should exert a pressure
on the great wheel of just a little less than the pull of the weight
on the barrel; they will then be compressed all the time the weight is
in action, and the stops will then transmit the power from the large
ratchet to the great wheel, which drives the train. Both the great
wheel and the large ratchet wheel are loose on the arbor, being pinned
close to the barrel, but free to revolve. A smaller ratchet, having
its teeth cut in the reverse direction from those of the larger one,
is fast to the end of the barrel. A click, called the winding click,
on the larger ratchet acts in the teeth of the smaller one during
the winding, holding the two ratchets together at all other times. A
longer click, called the detent click, is pivoted to the clock plate,
and drags idly over the teeth of the larger ratchet while the clock is
being driven by the weight and the maintaining springs are compressed.
When the power is taken off by the reversal of the barrel in winding,
the friction between the sides of the two ratchets and great wheel
would cause them to also turn backward, if it were not for this detent
click, with its end fast to the plate, which drops into the teeth of
the large ratchet and prevents it from turning backward. We now have
the large ratchet held motionless by the detent click on the clock
plate and the compressed springs which are carried between the large
ratchet and the great wheel will then begin to expand, driving the
loose great wheel until their force has been expended, or until winding
is completed, when they will again be compressed by the pull of the
weight. In some tower clocks curved pins are fixed to opposite spokes
of the great wheel and coiled springs are wound around the pins, Fig.
85; eyes in the large ratchet engage the outer ends of the pins and
compress the springs.
[Illustration: Fig. 86.]
The clicks for maintaining powers should not be short, and the
planting should be done so that lines drawn from the barrel center to
the click points and from the click centers to the points, will form
an obtuse angle, like B, Fig. 86, giving a tendency for the ratchet
tooth to draw the click towards the barrel center. The clicks should
be nicely formed, hardened and tempered and polished all over with
emery. Long, thin springs will be needed to keep the winding clicks up
to the ratchet teeth. The ratchet wheel must run freely on the barrel
arbor, being carried round by the clicks while the clock is going, and
standing still while the weight is being wound up. It is retained at
this time by a long detent click mounted on an arbor having its pivots
fitted to holes in the clock frame. The same remark as to planting
applies to this click as well as the others, and to all clicks having
similar objects; but as this click has its own weight to cause it to
fall no spring is required. To prevent it lying heavily on the wheel,
causing wear, friction and a diminution of driving power, it is as
well to have it made light. There is no absolute utility in fixing the
click to its collet with screws, but if done, it can be taken off to
be polished, and the appearance will be more workmanlike. This click
should have its point hardened and tempered, as there is considerable
wear on it.
[Illustration: Fig. 87.]
If the great wheel has spokes the best form for the two springs for
keeping the train going whilst being wound is that of the letter U, as
shown to the left of Fig. 84, one end enlarged for the screw and steady
pin and the blade tapering all along towards the end which is free.
The springs may be made straight and bent to the form while soft, then
hardened and tempered to a full blue. They are best when as large as
the space between two arms of the main wheel will allow. When screwed
on the large ratchet the backs of both should bear exactly against the
respective arms of the mainwheel, and a pair of pins is put in the
ratchet, so that any opposite pair of the mainwheel arms may rest upon
them when the springs are set up by the clock weight. The strength of
the springs can be adjusted by trial, reducing them till the weight of
the clock sets them up easily to the banking pins.
There are two methods of keeping the loose wheels against the end of
the barrel, while allowing them to turn freely during winding; one is a
sliding plate with a keyhole slot, Fig. 87, to slip in a groove on the
arbor, as is generally adopted in such house clocks as have fuzees, as
well as on the barrels of old-fashioned weight clocks; the other is a
collet exactly the same as on watch fuzees. They are both sufficiently
effective, but perhaps the latter is the best of the two, because the
collet may be fitted on the arbor with a pipe, and being turned true
on the broad inside face, gives a larger and steadier surface for the
mainwheel to work against, whereas the former only has a small bearing
on the shoulder of the small groove in the arbor, which fitting is
liable to wear and allow the main and the other loose wheel to wobble
sideways, displacing the contact with the detent click and causing
the mainwheel to touch the collet of the center wheel if very near
together; so, on the whole, a collet, as on a watch fuzee, seems the
better arrangement, where there is plenty of room for it on the arbor.
There is an older form of maintaining power which is sometimes met with
in tower clocks and which is sometimes imitated on a small scale by
jewelers who are using a cheap regulator and wish to add a maintaining
power where there is no room between the barrel and plates for the
ratchets and great wheel.
The maintaining power, Fig. 88, consists of a shaft, A, a straight
lever, B, a segment of a pinion, C, a curved, double lever, D, a
weight, E. The shaft, A, slides endwise to engage the teeth of the
pinion segment with the teeth of the great wheel. No. 2, the straight
lever has a handle at both ends to assist in throwing the pinion out or
in and a shield at the outer end to cover the end of the winding shaft,
No. 3, when the key is not on it.
The curved lever is double, and the pinion segment turns loosely
between the halves and on the shaft, A; it is held up in its place by a
light spring, F; the weight, E, is also held between the two halves of
the double lever.
[Illustration: Fig. 88. Maintaining Power.]
The action is as follows: The end of the lever, B, covers the end of
the winding shaft so that it is necessary to raise it before putting
the key on the winding shaft; it is raised till it strikes a stop, and
then pushed in till the pinion segment engages with the going wheel of
the train, when the weight, E, acting through the levers, furnishes
power to drive the clock train while the going weight is being
wound up. Of course the weight on the maintaining power must be so
proportioned to the leverage that it will be equal to the power of the
going barrel and its weight, a simple proposition in mechanics.
The number of teeth on the pinion segment, C, is sufficient to maintain
power for fifteen minutes, at the end of which time the lever, B, will
come down and again cover the end of the winding shaft; or, it may
be pumped out of gear and dropped down. In case it is forgotten, the
spring, F, will allow the segment to pass out of gear of itself and
will simply allow it to give a click as it slips over each tooth in the
going wheel; if this were not provided for, it would stop the clock.