MOTION WORK AND STRIKING TRAINS.
Motion work is the name given to the wheels and pinions used to make
the hour hand go once around the dial while the minute hand goes twelve
times. Here a few preliminary observations will do much toward clearing
up the operations of the trains. The reader will recollect that we
started at a fixed point in the time train, the center arbor which
must revolve once per hour, and increased this motion by making the
larger wheels drive the smaller (pinions) until we reached sixty or
more revolutions of the escape wheel to one of the center arbor. This
gearing to increase speed is called “gearing up” and in it the pinions
are always driven by the wheels. In the case of the hour hand we have
to obtain a slowing effect and we do so by making the smaller wheels
(pinions) drive the larger ones. This is called “gearing back” and it
is the only place in the clock where this method of gearing occurs.
We drew attention to a common usage in the gearing up of the time
trains—that of making the relations of the wheels and pinions 8 to one
and 7.5 to one; 7.5 × 8 = 60. So we find a like usage in our motion
work, viz., 3 to one and 4 to one; 3 × 4 = 12. Say the cannon pinion
has twelve teeth; then the minute wheel generally has 36, or three to
one, and if the minute wheel pinion has 10, the hour wheel will have
40, or four to one. Of course, any numbers of wheels and pinions may
be used to obtain the same result, so long as the teeth of the wheels
multiplied together give a product which is twelve times that of the
pinions multiplied together; but three and four to one have been
settled upon, just as the usage in the train became fixed, and for the
same reasons; that is, these proportions take up the least room and may
be made with the least material. Also, the pinion with the greatest
number of teeth, being the larger, is usually selected as the cannon
pinion, as it gives more room to be bored out to receive the cannon,
or pipe. If placed outside the clock plate, the minute wheel and
pinion revolve on a stud in the clock plate; but if placed between the
frames, they are mounted on arbors like the other wheels. The method of
mounting is merely a matter of convenience in the arrangement of the
train and is varied according to the amount of room in the movement, or
convenience in assembling the movement at the factory, little attention
being paid to other considerations.
[Illustration: Fig. 89. Fig. 90.]
The cannon pinion is loose on the center arbor and behind it is a
spring, called the center spring, or “friction,” Figs. 89 and 90, which
is a disc that is squared on the arbor at its center and presses at
three points on its outer edge against the side of the cannon pinion;
or it may be two or three coils of brass wire. This center spring thus
produces friction enough on the cannon to drive it and the hour hand,
while permitting the hands to be turned backward or forward without
interfering with the train. In French mantel clocks the center spring
is dispensed with and a portion of the pipe is thinned and pressed in
so as to produce a friction between the pipe and the center arbor which
is sufficient to drive the hands; this is similar to the friction of
the cannon pinion in a watch.
[Illustration: Fig. 91.]
In some old English house clocks with snail strike, the cannon pinion
and minute wheel have the same number of teeth for convenience in
letting off the striking work by means of the minute wheel, which thus
turns once in an hour. Where this is the case the hour wheel and its
pinion bear a proportion to each other of twelve to one; usually there
is a pinion of six leaves engaging a wheel of 72 teeth, or seven and
eighty-four are sometimes found.
In tower clocks, where the striking is not discharged by the motion
work, the cannon pinion is tight on its arbor and the motion work is
similar to that of watches. See Fig. 91.
The cannon pinion drives the minute wheel, which, together with its
pinion, revolves loosely on a stud in the clock plate, or on an arbor
between the frames. The meshing of the minute wheel and cannon pinion
should be as deep as is consistent with perfect freedom, as should also
that of the hour wheel and minute pinion in order to prevent the hour
hand from having too much shake, as the minute wheel and pinion are
loose on the stud and the hour wheel is loose on the cannon, so that
a shallow depthing here will give considerable back lash, which is
especially noticeable when winding.
The hour wheel has a short pipe and runs loosely on the cannon pinion
in ordinary clocks. In quarter-strike cuckoos a different train is
employed and the wheels for the hands are both on a long stud in the
plate and both have pipes; the minute wheel has 32 teeth and carries
four pins on its under side to let off the quarters. The hour wheel
has 64 teeth and works close to the minute wheel, its pipe surrounding
the minute wheel pipe, and held in position by a screw and nut on the
minute pipe. A wheel of 48 and a pinion of 8 teeth are mounted on the
sprocket arbor with a center spring for a friction, the wheel of 48
meshing with the minute wheel of 32 and the 8-leaf pinion with the hour
wheel of 64. It will be recollected that the sprocket wheel takes the
place of the barrel in this clock and there is no center arbor as it is
commonly understood. The sprocket arbor in this case turns once in an
hour and a half, hence it requires 48 teeth to drive the minute wheel
of 32 once in an hour, as it turns one-third of a revolution (or 16
teeth) every half hour. The sprocket arbor, turning once in an hour and
a half, makes eight revolutions in twelve hours and its pinion of eight
leaves working in the hour wheel of 64 teeth turns the hour hand once
in twelve hours.
In ordinary rack and snail striking work the snail is generally mounted
on the pipe of the hour wheel, so that it will always agree with the
position of the hour hand and the striking will thus be in harmony with
the position of the hands.
STRIKING TRAINS.--It is only natural, after finding certain fixed
relations in the calculations of time trains and motion work, that we
should look for a similar point in striking trains, well assured that
we shall find it here also. It is evident that the clock must strike
the sum of the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 78
blows of the hammer, in striking from noon to midnight; this will be
repeated from midnight to noon, making 156 blows in 24 hours, and if it
is a 30-hour clock, six hours more must be added; blows for these will
be 21 more, making a total of 177 blows of the hammer for a 30-hour
strike train. The hammer is raised by pins set in the edge of a wheel,
called the pin wheel, and as one pin must pass the hammer tail for
every blow, it is evident that the number of pins in this wheel will
govern the number of revolutions it must make for 177 blows, so that
here is the base or starting point in our striking train. If there are
13 pins in the pin wheel, it must revolve 13.5 times for 177 blows; if
there are 8 pins, then the wheel must revolve 22.125 times in giving
177 blows; consequently the pinions and wheels back to the spring or
barrel must be arranged to give the proper number of revolutions of the
pin wheel with a reasonable number of turns of the spring or weight
cord, and it is generally desirable to give the same, or nearly the
same, number of turns to both time and striking barrels.
If it is an eight-day clock the calculation is a little different.
There are 156 blows every 24 hours; then as the majority of “eight-day”
clocks are really calculated to keep time for seven and a half days,
although they will run eight, we have: 156 × 7.5 = 1,070 blows in 7.5
days. With 13 pins we have 1,070 ÷ 13 = 80 and ⁴/₁₃ths revolutions in
the 7.5 days. If now we put an 8-leaf pinion on the pin wheel arbor and
84 teeth in the great wheel or barrel, we will get 10.5 turns of the
pin wheel for every turn of the spring or barrel; consequently eight
turns of the spring will be enough to run the clock for the required
time, as such clocks are wound every seventh day.
Figuring forward from the pin wheel, we find that we shall have to lock
our striking train after a stated number of blows of the hammer each
hour; these periods increase by regular steps of one blow every hour,
so that we must have our locking mechanism in position to act after
the passage of each pin, whether it is then used or not; so the pinion
that meshes with the pin wheel, and carries the locking plate or pin
on its arbor must make one revolution every time it passes a pin. If
this is a 6-leaf pinion, the pins on the pin wheel must therefore be 6
teeth apart; or an 8-leaf pinion must have the pins 8 teeth apart; and
vice versa. For greater convenience in registering, the pins are set in
a radial line with the spaces of the teeth in the pin wheel, as this
allows us to measure from the center of the pinion leaf.
It will thus be seen that the calculation of an hour striking train
is a simple matter; but if half hours are also to be struck from the
train, it will change these calculations. For a 30-hour train 24 must
be added to the 156 blows for 24 hours, 180 blows being required to
strike hours and half hours for 24 hours. These blows may be provided
for by more turns of the spring, or different numbers of the wheels and
pinions, which would then also vary the spacing of the pins.
Half hours may also be struck directly from the center arbor, by
putting an extra hammer tail on the hammer arbor, further back,
where it will not interfere with the hammer tail for the pin wheel,
and putting a cam on the center arbor to operate this second hammer
tail. This simplifies the train, as it enables the use of a shorter
spring or smaller wheels while providing a cheap and certain means of
striking the half hours. Half-hour trains are frequently provided with
a separate bell of different tone for the half hours, as with only one
bell the clock strikes one blow at 12:30, 1 and 1:30, making the time
a matter of doubt to one who listens without looking, as frequently
happens in the night.
[Illustration: Fig. 92. Eight Day Hour and Half Hour Strike.]
Fig. 92 shows an eight-day, Seth Thomas movement, which strikes the
hours on a count wheel train and the half hours from the center arbor.
All the wheels, pinions, arbors, pins, levers and hooks are correctly
shown in proper position, but the front plate has been left off for
greater clearness. The reader will therefore be required to remember
that the escape wheel, pallets, crutch, pendulum and the stud for the
pendulum suspension are really fixed to the front plate, while in the
drawing they have no visible means of support, because the plate is
left off.
The time train occupies the right-hand side of the movement and the
striking train the left hand. Running up the right-hand from the
spring to the escape wheel, we find an extra wheel and pinion which is
provided to secure the eight days’ run. We also see that what would
ordinarily be the center arbor is up in the right corner and does not
carry the hands; further, the train is bent over at a right angle,
in order to save space and get the escape wheel in the center at the
top of the movement. The striking train is also crowded down out of
a straight line, the locking cam being to the right of the pin wheel
and the warning wheel and fly as close to the center as possible. This
leaves some space between the pin wheel and the intermediate wheel
of the time train and here we find our center arbor, driven from the
intermediate wheel by an extra pinion on the minute wheel arbor, the
minute wheel meshing with the cannon pinion on the center arbor. This
rearranging of trains to save space is frequently done and often shows
considerable ingenuity and skill; it also will many times serve to
identify the maker of a movement when its origin is a matter of doubt
and we need some material, so that the planting of trains is not only
a matter of interest, but should be studied, as familiarity with the
methods of various factories is frequently of service to the watchmaker.
Fig. 93 is the upper portion of the same striking train, drawn to a
larger scale for the sake of clearness. It also shows the center arbor,
both hammer tails and the stop on the hammer arbor, which strikes
against the bottom of the front plate to prevent the hammer-spring from
throwing the hammer out of reach of the pins. The pin wheel, R, and
count wheel, E, are mounted close together and are about the same size,
so that they are shown broken away for a part of their circumferences
for greater clearness in explaining the action of the locking hook, C,
and the locking cam, D.
Fig. 94 shows the same parts in the striking position, being shown as
just about to strike the last blow of 12. Similar parts have similar
letters in both figures.
The count wheel, E, is loose on a stud in the plate, concentric with
the arbor of the pin wheel, R. The pivot of R runs through this stud.
The sole office of the count wheel is to regulate the distance to which
the locking hook C, is allowed to fall. The count hook, A, and the
locking hook, C, are mounted on the same arbor, B, so that they move in
unison. If A is allowed to fall into a deep slot of the count wheel, C
will fall far enough to engage the locking face of the cam D and stop
the train, as in Fig. 93. If, on the contrary, A drops on the rim of
the wheel, C will be held out of the locking position as D comes around
(see Fig. 94), and the train will keep on running. It will be seen that
after passing the locking notch, D, Fig. 94, will in its turn raise the
hook C, which will ride on the edge of D, and hold A clear of the count
wheel until the locking notch of D is again reached, when a deep notch
in the wheel will allow C to catch, as in Fig. 93, unless C is stopped
by A falling on the rim of the wheel, as in Fig. 94.
[Illustration: Fig. 93. Upper Portion of Striking Train Locked.]
[Illustration: Fig. 94. Striking Train Unlocked and Running.]
One leaf, F, of the pinion of the locking arbor sticks out far enough
to engage with the count wheel teeth and rotate the wheel one tooth for
each revolution of D, so that F forms a one-leaf pinion similar to that
of a rack striking train. Here we have our counting mechanism; F and D
go around together; F moves E one tooth every revolution. A holds C out
of action (Fig. 94) until A reaches a deep slot, when C stops the train
by engaging D (Fig. 93).
The count wheel, E, must have friction enough on its stud so that it
will stay where the pin F leaves it, when F goes out of action and
thus it will be in the right position to suitably engage F on the next
revolution. Too much friction of the count wheel on its stud will use
too much power for F to move it and thus slow the train; if there is
too little friction here the count wheel may get in such a position
that F will get stalled on the top of a tooth and stop the train.
The count hook, A, must strike exactly in the middle of the deep slots,
without touching the sides of the slots in entering or leaving, as to
do this would shift the position of the count wheel if the rubbing were
sufficient, or it might prevent A from falling (as A and C are both
very light) and the clock would go on striking. If the hook A does not
strike the middle of the spaces between the teeth of the count wheel,
it will gradually encroach on a tooth and push the wheel forward or
back, thus disarranging the count. Many a clock has struck 13 for 12
in this way because the hook was a little out. This did not occur in
the smaller numbers because the action was not continued long enough to
allow the hook to reach a tooth. The pin, F, should also mesh fairly
and freely in the teeth of the count wheel, or a similar defect is
likely to occur.
When repairing or making new count hooks, A, Figs. 93 and 94, they must
be of such a length that they will enter the slots on a line radial
with the center of the wheel. The proper length and direction are shown
at A, Fig. 95, while B and C are wrong. With hooks like either B or C
you can set or bend the hook to strike right at one and as you turn
the clock ahead the hook does not fall in far enough and at twelve it
only strikes eleven. Then if you bend the same hook to strike right
at twelve it will strike two at one and as you turn the clock ahead
it will strike right at about five or seven. A, Fig. 95, being of the
proper length and shape will give no trouble. Many of the count wheels
of the older clocks were divided by hand and are not as accurate as
they should be; when a wheel of this kind is found and a new wheel
cannot be substituted (because the clock is an antique and must have
the original parts preserved) it will sometimes require nice management
of the hook A to obtain correct striking. A little manipulation of the
pinion, F, Fig. 93 is sometimes desirable also, if the count wheel is
very bad.
[Illustration: Fig. 95. The proper length of the count hook.]
The locking face of the cam, D, must also be on a line radial to its
center, or it will either unlock too easily and go off on the slightest
jar or movement of the clock, or the face will have too much draw and
the hook C will not be unlocked when the clock is fully wound, and the
spring pressure is greatest. In this case the clock will not strike
when fully wound, but will do so when partly run down, and as the count
wheel train strikes in rotation, without regard to the position of
the hands, you will have irregular striking of a most puzzling sort.
Repairs to this notch are sometimes required, when the corner has
become rounded, and the best way to make them is to cut a new face on
the cam with a sharp graver, being careful to keep the face radial with
its center.
Because the count wheel strikes the hours in rotation, regardless of
the position of the hands, if the hands are turned backwards past the
figure 12 on the dial the striking will be thrown out of harmony with
the hands. To remedy this the count hook, A, has an eye on its rear end
and a wire, shown in Fig. 92, hangs down to where it can be reached
with the hand when the dial is on. Pulling this wire will lift A and C
and cause the clock to strike; by this means the clock may be struck
around until the position of the striking train agrees with that of
the hands. Where this wire is not present the striking is corrected by
turning the hands back and forth between IX and XII until the proper
hour is struck.
Now we come to the releasing mechanism, which causes the clock to
strike at stated times. I, Figs. 93 and 94, is an arbor pivoted
between the plates and carrying three levers, H, K and J, in different
positions on the arbor. H is directly under the count hook, A, and
lifts A and C whenever J is pushed far enough to one side by L on the
center arbor, which revolves once an hour. Thus L, through J, H and A,
C, unlocks the train once every hour. When C is thus lifted the train
runs until the warning pin, O, Figs. 93 and 94, strikes against the
lever K, which is on the same arbor with H and J. This preliminary run
of the train makes a little noise and is called “warning,” as the noise
notifies us that the train is in position to commence striking. The
lever K and the warning pin, O, then hold the train until L has been
carried out of action with J and released it, when O will push K out of
its path at every revolution and the clock will strike.
The half hours are struck by L¹ pressing the short hammer tail, G¹,
and thus raising and releasing the hammer once an hour.
In setting up the striking train after cleaning, place the pin wheel
so that the hammer tail, G, may be about one-fourth of the distance
from the next pin, as shown in Fig. 93; this allows the train to get
well under way before meeting with any resistance and will insure its
striking when nearly run down. If the hammer tail is too close to the
pin, it might stop the train when there is but little power on.
Then place D in the locked position, with A in a deep slot of the count
wheel and C in the notch of D. Next place the warning wheel with its
pin, O, on the opposite side of its arbor from the lever K, see Fig.
93. This is done to make sure that when it is unlocked for “warning”
the train will run far enough to get the corner of the lock, D, safely,
past C, so that it will not allow C to fall into the notch again and
lock the train when J, K and H are released by L. This is the rule
followed in assembling these clocks at the factories and is simple,
correct and easily understood. A study of these points in Fig. 93 will
enable any one to set up a train correctly before putting the front
plate on.
If the workman gets a clock that has been butchered by some one who
did not understand it (and there are many such), he may find that when
correctly set up the clock does not strike on the 60th minute of the
hour; in such a case a little bending of J, in or out as the case may
be, will usually remedy the trouble. The same thing may have to be done
to the hammer tails, G and G¹, or the stop on the hammer arbor. If
both hammer tails are out of position, bend the stop; if one is right,
let the stop alone and bend the other tail.
A rough, set or gummy spring will cause irregular striking. In such
a case the clock will strike part of the blows and then stop and
finally go on again and complete the number. Much time has been lost
in examining the teeth of wheels and pinions in such cases when the
trouble lay in the spring. Too strong a spring will make the movement
strike too fast; too weak a spring will make it strike slow, especially
in the latter part of the day or week, when it has nearly run down.
Too small a fan, or a fan that is loose on its arbor, will allow the
clock to strike too fast. If this fan is badly out of balance it will
prevent the train from starting when there is but little power on.
There is a class of clocks which have the count wheel tight on the
arbor, outside the clock plate. Many of them are on much tighter than
they should be. In such a case take an alcohol lamp and heat the wheel
evenly, especially around the hub; the brass will expand twice as much
as the steel and the wheel may then be driven off without injury.
Fig. 96 shows another typical American eight-day train, made by the
Gilbert Clock Company, and striking the half hours from the train.
Here we notice, on comparing with Fig. 92, that there are many points
of difference. First the notches on the count wheel are twice as wide
as they are in Fig. 92. This means that half hours are struck on the
train; this will be explained later. Next there are two complete sets
of notches on the wheel, which shows that the wheel turns only once
in twenty-four hours, whereas the other makes two revolutions in that
time. There are no teeth on the count wheel, so that it must be fast
to its arbor, which is that of the great wheel and spring, while Fig.
92 has a separate stud and it is loose. The wheel being on the spring
arbor and going once in 24 hours, there must be one turn of spring for
each 24 hours which the train runs. There is no pin wheel in Fig. 96,
but instead of this two pins are cut out of the locking cam to raise
the hammer tail as they pass. There are also two locking notches in
the locking cam. The cams on the center arbor are stamped out of brass
sheet, while those of Fig. 92 were of wire.
[Illustration: Fig. 96. Half hours struck on the train.]
Turning to the enlarged view in Fig. 97 and comparing it with Fig. 93,
we find further differences. The levers K and J are here made of one
piece of brass, while the others were separate and of wire. The lifting
lever, H, is flattened at its outer end in Fig. 93, while in Fig. 97
it is bent at right angles and passed under the count hook, A. The
hook, C, Fig. 97, is added to the arbor, B, as a safety device, in case
the locking hook should fail to enter its slot in the cam, D. It is
shown as having just stopped the warning pin in Fig. 96. There is but
one hammer tail, G, and the hammer stop acts against the stud for the
hammer-spring, instead of against the bottom of the front plate, as in
Fig. 92.
The first important difference here is in the position of the count
hook, A. In Figs. 92 and 93 the hook must be exactly in the middle of
the slot, or there will be trouble. In trains striking half hours from
the train, we must never allow the hook to occupy the middle of the
slot, or we will have more trouble than we ever dreamed of. In this
instance the count hook must enter the slot close to (but not touching)
the side of the slot when the clock stops striking; then when the half
hour is struck the count wheel will move a little and the hook must
drop back into the same slot without touching; this brings it close to
the opposite side of the same slot and the next movement will land the
hook safely on top of the wheel for the strokes of the hour. Fig. 96
shows its position after striking the half hour and ready to strike the
hour of two. Fig. 97 shows it dropping back after striking two.
[Illustration: Fig. 97. Half hour strike on the count wheel.]
In setting up this train, see that the count hook. A, goes into the
slot of the count wheel close to, but not touching, one side of the
slot in the count wheel, and, after placing the intermediate, insert
the locking cam, D, so that it engages the locking hook; then put in
the warning wheel with the warning pin, O, safely to the left of the
hook C, Fig. 97, so that it cannot get past that hook after striking.
Placing the wheel with its warning pin six or eight teeth to the left
of the edge of the bottom plate is generally about right. The action of
the levers, H, J, K, the hammer tail, G, and the cam, L, in striking
the hours is the same as that already described in detail for Figs. 93
and 94, hence need not be repeated here. L¹ strikes the half hours by
being enough shorter than L to raise the hooks for one revolution, but
not quite so high as for the hours. The cams L, L¹ are friction-tight
on the center arbor and may be shifted on the arbor to register the
striking on the 60th minute, if desired. When the hands and strike do
not agree, turn the minute hand back and forward between IX and XII,
thus striking the clock around until it agrees with the hands.
Sometimes, if the warning pin is not far enough away, an eight-day
clock will strike all right for a number of days and then commence
to gain or lose on the striking side. It either does not strike at
some hours, or half hours, or it may strike sometimes both hour and
half hour before stopping. Take the movement out of the case and put
the hands on; then move the minute hand around slowly until the clock
warns. Look carefully and be sure there is no danger of the clock
striking when it warns. If this looks secure, then move the hand to
the hour, making it strike; say it is going to strike 9 o’clock; when
it has struck eight times, stop the train with your finger and let the
wheels run very slow while striking the last one, and when the rod
drops into the last notch stop the train again and hold it there.
For the striking part to be correct, the warning pin on the wheel wants
to be about one-fourth of a revolution away from the rod when the clock
has struck the last time, or as soon as this rod falls down far enough
to catch the pin. The object of this is so there is no chance of the
warning pin getting past the rod at the last stroke; this it is liable
to do if the pin is too close to the rod when the rod drops. If you
will examine the clock as above, not only when it strikes IX, but all
the hours from I to XII, you will generally find the fault. Of course,
if the pin is too close to the rod when the rod drops, you must lift
the plates apart and change the wheel so that the warning pin and the
rod will be as explained.
SHIP’S BELL STRIKING WORK.--Of all the count wheel striking work which
comes to the watchmaker, the ship’s bell is most apt to give him
trouble. This generally arises from ignorance as to what the system of
bells on shipboard consists of and how they should be struck. If he
goes to some nautical friend, he hears of long and short “watches” or
“full watches” and “dog watches.” If he insists on details, he gets the
information that a “watch” is not a horological mechanism, but a period
of duty for a part of the crew. Then he is told of the “morning watch,”
“first dog watch,” “afternoon watch,” “second dog watch,” “off watch,”
“on watch,” etc. Now the ship’s bell clock does not agree with these
“watches” and was never intended to do so. As a matter of fact, it is
simply a clock striking half hours from one to eight and then repeating
through the twenty-four hours.
The striking is peculiarly timed and is an imitation of the method in
which the hours are struck on the bell of the ship. As this bell is
also used for other purposes, such as tolling in fogs, fire alarms,
church services, etc., it will readily be seen that a different method
of striking for each purpose is desirable to avoid misunderstanding of
signals.
[Illustration: Fig. 98. Ships bell clock.]
The method of striking for time is to give the blows in couples, with a
short interval between the strokes of the couples and three times that
interval between the couples. Odd strokes are treated as a portion of
the next couple and separated accordingly, thus:
12:30 p. m. One Bell, O
1:00 p. m. Two Bells, O O
1:30 p. m. Three Bells, O O O
2:00 p. m. Four Bells, O O O O
2:30 p. m. Five Bells, O O O O O
3:00 p. m. Six Bells, O O O O O O
3:30 p. m. Seven Bells, O O O O O O O
4:00 p. m. Eight Bells, O O O O O O O O
After striking eight bells the clock repeats, although the ship’s bell
is generally struck in accordance with the two dog watches (which are
of two hours’ duration each) before commencing the evening watch (8 to
12 p. m.). It will thus be seen that the clock should strike eight at
12 m., 4 p. m., 8 p. m., 12 p. m., 4 a. m., and 8 a. m.
[Illustration: Fig. 100. The pins on the count wheel of the ships bell
clock.]
In order to strike the blows in pairs two hammers are necessary, see
Fig. 98; these hammers are placed close together, but not in the same
plane. The pin wheel has twenty pins, see Figs. 98, 99, 100; some of
these pins are shorter than the others, so that they do not operate one
of the hammer tails. These are shown graphically in Fig. 100; where
the two oblong marks at figure 1 represent the tops of the hammer
tails shown in Fig. 99. It will be seen by studying Fig. 100 that with
the wheel moving from left to right, the inside hammer tail will be
operated for one blow, while the outer hammer tail will not be operated
at all, thus giving but one blow, or “bell.” At the next movement of
the pin wheel, the outside hammer will be operated by the long pin
and the inside hammer by the short pin, thus giving one blow of each
hammer, or “two bells.”
[Illustration: Fig. 99. Enlarged view of striking work, ships bell
clock.]
We now have these hammer tails advanced along the wheel so that the
outside one is opposite the figure 3 in the drawing, while the other is
opposite the figure 2, with one pin between them. The next movement of
the pin wheel advances them so that the outside hammer will pass the
next short pin and consequently that hammer will miss one blow and the
pair will therefore strike three—one by the outside hammer and two by
the inside. It thus goes on until the cycle is completed, eight blows
being struck with the last four pins. The striking in pairs is effected
by having the two hammer tails close together, so that the pins will
operate both hammer tails quickly and there will then be an interval of
time while the wheel brings forward the next pins. This is so spaced
that the interval between pairs is three times that between the blows
of a pair and the hammer tails should not be bent out of this position,
or if found so they should immediately be restored to it. Tolling the
bells, instead of striking them properly, is very bad form at sea and
generally leads to punishment if persisted in, so that the jeweler will
readily perceive that his marine customers are very particular on this
point, and he should go any length to obtain the proper intervals in
striking.
The pin wheel moves forward one pin for each couple of blows or parts
of a couple, the odd blows being secured by the failure of the blow
when the hammer tail passes the short pin. Thus it moves as far for one
bell as for two bells; as far for three bells as for four, etc. The
result is that the count wheel has no odd numbers on it, but instead
two 2’s, two 4’s, two 6’s and two 8’s; the first two are counted on
the count wheel, but only one is struck on the pin wheel, owing to
the short pin; this is repeated at three, five and seven, when four,
six and eight are counted on the wheel, but the last blow fails of
delivery, owing to the short pin in the pin wheel at these positions.
The center arbor carries two pins, L and L¹, to unlock the train
through the lever J, as it is really a half hour striking clock. The
count hook, A; locking hook, C; count wheel, E; pins, P, and other
parts have similar letters for similar parts as in the preceding
figures and need not be further explained, as the mechanism is
otherwise similar to the Seth Thomas movement shown in Fig. 92.