SNAIL STRIKING WORK, ENGLISH, FRENCH AND AMERICAN.
While the majority of snail striking movements made in America are on
the French system, because they are cheaper when made in that way,
still this system is so condensed and so difficult to illustrate, with
all its mechanism packed in a small space between the plates, that
the student will gain a much better idea of the rack and snail and
its principles by first making a study of an English snail striking
clock, which has the whole of the counting and releasing levers placed
outside the front plate, where they can occupy all the room that may be
necessary. The calculation and planting of the striking train do not
differ from those using the count wheel, up to and including the single
toothed pinion or gathering pallet. The stopping of the train after
striking is different and the counting is divided, being dependent upon
four pieces acting in conjunction in an hour strike of the simplest
order, which number may run to a dozen in a repeating clock.
As the count wheel system had the defect of getting out of harmony with
the hands when the latter are turned backward, so the snail system has
its defects, which are the displacement of the rack and failure to stop
the striking in some clocks if the striking train runs down before
the time side and is then rewound, and a most puzzling inaccuracy of
counting, resulting from slight wear and inaccuracy of adjustment.
We mention these things here because they have an influence on the
construction of the clock and an advance knowledge of them will serve
to make clearer some of the statements which follow.
HOUR AND HALF-HOUR SNAIL STRIKING WORK.—Fig. 104 is a view of the front
plate of an English fusee striking clock, on the rack principle. The
going train occupies the right and center and the striking train the
left hand. The position of the trains is indicated in dotted lines,
the trains having barrels and fusees as shown by the squared arbors,
all the dotted work being between the clock plates, and that in full
lines being placed on the outside of the front plate, under the dial.
The connection between the going train and the striking work is by
means of the motion wheel on the center arbor, and connection is made
between the striking train and the counting work by the gathering
pallet, F, which is fixed to the arbor of the last wheel but one of the
striking train, and also by the warning piece, which is shown in black
on the boss of the lifting piece, A. This warning piece goes through a
slotted hole in the plate, and during the interval between warning and
striking stands in the path of a warning pin in the last wheel of the
striking train. The motion wheel on the center arbor, turning once in
an hour, gears with the minute wheel, E, which has an equal number of
teeth. There are two pins opposite each other and equidistant from the
center of the minute wheel, which in passing raise the lifting piece,
A, every half hour. Except for a few minutes before the clock strikes,
the striking train is kept from running by the tail of the gathering
pallet; F, resting on a pin in the rack, C. Just before the hour, as
the boss of the lifting piece, A, lifts the rack hook B, the rack C,
impelled by a spring in its tail, falls back until the pin in the lower
arm of the rack is stopped by the snail, D. This occurs before the
lifting piece, A, is released by the pin in the minute wheel, E, and in
this position the warning piece stops the train. Exactly at the hour
the pin in the minute wheel, E, gets past the lifting piece, A, which
then falls, and the train is free. For every blow struck by the hammer
the gathering pallet, F, which is really a one-toothed pinion, gathers
up one tooth of the rack, C, which is then held, tooth by tooth, by
the point of the hook, B. After the pinion, F, has gathered up the last
tooth, its tail is caught by the pin in the rack, which stops and locks
the train, and the striking ceases.
The snail, O, is mounted on a twelve-toothed star wheel, placed on a
stud in the plate, so that a pin in the motion wheel on the center
arbor moves it one tooth for each revolution of the motion wheel, and
it is then held in position by the click and spring as shown. The pin,
in moving the star wheel, presses back the click, which not only keeps
the star wheel steady, but also completes its forward motion after the
pin has pushed the tooth past the projecting center of the click. The
steps of the snail are arranged so that at one o’clock it permits only
sufficient fall of the rack for one tooth to be gathered up, and at
every succeeding hour gives the rack an additional motion equal to one
extra tooth. It will be seen that where a star wheel is used a cord or
wire attached to A and run outside the case, so that A may be lifted,
will cause the clock to repeat the hour whenever desired.
The lower arm of the rack, C, and the lower arm of the lifting piece,
A, are made of brass, and thin, so as to yield when the hands of the
clock are turned back; the lower extremity of the lifting piece, A, is
a little wider, and bent to a slight angle with the plane of the arm,
so as not to butt as it comes into contact with the pin when this is
being done. If the clock is not required to repeat, the snail may be
placed upon the center arbor, instead of on a stud with a star wheel
as shown, and this is generally done with the cheaper class of hour
striking clocks; but the position of the snail is not then so definite,
owing to the backlash of the motion wheels, so that it will not repeat
correctly, as the pin of the rack may fall on a slope of the snail and,
besides, a smaller snail must be used, unless it is brought out to
clear the nose of the minute wheel cock, or bridge if one be used.
[Illustration: Fig. 104. Hour and half hour snail striking work with
fusee train.]
HALF-HOUR STRIKING.—The usual way of getting the clock to strike one
at the half-hour, is by making the first tooth of the rack, C, lower
than the rest, and placing the second pin in the minute wheel, E, a
little nearer the center than the hour pin, so that the rack hook,
B, is lifted free of the first tooth only at the half hour. But this
adjustment is too delicate after some wear has occurred and the action
is then liable to fail altogether or to strike the full hour, from the
pin getting bent or from uneven wear of the parts. The arrangement
shown in Fig. 104 is generally used in English work, as it is much
safer. One arm of a bell-crank lever rests on a cam fixed to the minute
wheel, E. This arm is shaped so that just before the half-hour the
other extremity of the bell-crank lever catches a pin placed in the
rack, C, and permits it to release the train and fall the distance
of but one tooth. This is the position shown in Fig. 104. After the
half-hour has struck, the cam carries the hook free from the pin in C.
[Illustration: Fig. 105. Rack, showing method of getting sizes of snail
steps according to distance from the rack center to the pin in the rack
tail.]
DIVISION OF THE HOUR SNAIL.—The length of the rack tail, from the
center of the stud hole in the rack to the center of the pin, should
be equal to the distance between the center of the stud hole and the
center of the snail. The difference between the radius of the top and
the radius of the bottom step of the snail may be obtained by getting
the angular distance of twelve teeth of the rack from center to pin.
See A B, C D, E F, Fig. 105, which show the total distances for twelve
steps of the snail for rack tails of different lengths. Divide the
circumference of a piece of brass into twelve parts and draw radial
lines as shown in Fig. 106. Each of these spaces is devoted to a step
of the snail. Draw circles representing the top and bottom step. Divide
the distance, A B or E F, Fig. 105, between these two circles, into
eleven equal parts, and at each division draw a circle which will
represent a step of the snail. The rise from one step to another should
be sloped as shown, so as to raise the pin in the rack arm if the
striking train has been allowed to run down, and it should be resting
on the snail when it is desired to turn the hands back. The rise from
the bottom to the top step is bevelled off, so as to push the pin in
the rack arm on one side, by springing the thin brass of the arm and
allow it to ride over the snail if it is in the way when the clock is
going. It should also be curved to avoid interference with the pin.
Clockmakers making new snails when repairing generally mark off the
snail on the clock itself after the rest of the striking work is in
position. A steel pointer is fixed in the hole of the lower rack arm,
and the star wheel jumped forward twelve teeth (one at a time) by means
of the pin in the motion wheel. After each jump a line is marked on the
blank snail with the pointer in the rack arm by moving the rack arm.
These twelve lines correspond to the twelve radial lines in Fig. 106.
The motion wheel is then turned sufficiently to carry the pin in it
free of the star wheel and leave the star wheel and blank snail quite
free on their stud. The rack hook is placed in the first tooth of the
rack, and while the pointer in the rack arm is pressed on the blank
snail, the latter is rotated a little, so that a curve is traced on
it. The rack hook is then placed in the second, and afterwards in the
succeeding teeth consecutively, and the operation repeated till the
twelve curves are marked. There is one advantage in marking off the
snail in this way. Should there be any inaccuracy in the division of
the teeth of the rack, the steps of the snail are thus varied to suit
it. This frequently occurs in old clocks which have had new racks filed
up by hand by some watchmaker.
Reference to the drawing, Fig. 105, will show that the rack is laid out
as a segment of a wheel with teeth occupying two degrees each, with a
few teeth added for safety. Fourteen to sixteen teeth are generally
provided, for the following reasons: If the first tooth is used to
strike the half hours, it may in time become worn so that it can no
longer be stretched to its proper length. In such cases moving the pin
two degrees nearer the rack teeth will allow us to use the teeth from
the second to the thirteenth in striking twelve, which makes a cheap
and easy repair, as compared to inserting a new tooth or making a new
rack.
Weight driven snail clocks should have the weight cords of the striking
side long enough so that the striking train will not run down before
the time train, as in such a case the rack tail is pushed to one side
by the progress of the snail (which is carried on the time train and
is still running); then the rack will drop clear out of reach of the
gathering pallet and when the striking train is wound that train will
continue striking until it runs down, or the dial is removed and the
rack replaced in mesh with the gathering pallet. This happens with
short racks and with large, old-fashioned snails. By leaving a few more
teeth in the rack the rack tail will strike the stud, or hour wheel
sleeve, before the rack teeth get out of reach of the gathering pallet.
Many watchmakers put a stud or pin in the plate to stop the rack from
falling beyond the twelfth step, to prevent troubles of this kind.
The rack tail is friction-tight on its arbor and should be adjusted so
that the proper tooth shall come in mesh with the gathering pallet for
each step of the snail, or irregular striking will result. Such a clock
may strike one, two, three and four correctly and then strike six for
five, or seven or nine for eight, or thirteen for twelve, or it may
strike one or two hours wrong and the rest correctly. This is because
the gathering pallet, F, Fig. 104, does not carry the rack teeth safely
past the edge of the rack hook, B, owing to the tail of the rack not
being properly adjusted. The teeth should all be carried safely past
the edge of the hook and then be dropped back a little as the hook
engages; this is the more necessary to watch with hand-made racks and
snails, or after putting in a new, and therefore larger, pin in the
rack tail to replace one which is badly worn.
[Illustration: Fig. 106. Laying out steps of snail.]
The snail should be put on so that the pin in the rack tail will strike
the center of each step, or there is danger of irregular striking, or
of failure to strike twelve, owing to the pin striking the surface of
the cam midway between one and twelve and thus preventing the rack
from falling the requisite number of teeth. When this occurs the clock
will jam and stop.
The rack hook, B, Fig. 104, should be lifted far enough so that the
rack will fall clear of the hook without the teeth catching and making
a rattling noise as they pass the hook. In many old hour strikes the
first tooth of the rack is left longer than the rest to ensure this
freedom of passage when the rack is released.
The gathering pallet, F, is the weakest member of the system and will
be very likely to be split or worn out in clocks brought in for repair.
It should be squared on its arbor, or pinned, but many are not. If
split, and the arbor is round, where the pallet is put on, it may cause
irregular striking by opening on the arbor and permitting the train
to run when the tail strikes the pin in the rack. A new one should be
made so as to lift one tooth and a very little of the next one at each
revolution. It is necessary to cause the gathering pallet to lift a
little more than one tooth of the rack, and let it fall back again, to
insure that one will always be lifted; because if such was not the case
the clock would strike irregularly, and would also be liable sometimes
to strike on continually till it ran down. If the striking part is
locked by the tail of the gathering pallet catching on a pin in the
rack, the tail should be of a shape that will best prevent the rack
from falling back when the clock warns for striking the next hour; and
of course the acting faces of the pallet must be perfectly smooth and
polished.
The teeth of the rack may require dressing up in some cases and to
allow this to be done the rack may be stretched a little at the stem,
with a smooth-faced hammer, on a smooth anvil; or, if it wants much
stretching, take the pene of the hammer and strike on the back, with
the front lying on the smooth anvil. The point of the rack hook, B,
will probably be much worn, and when dressing it up it will be safe
to keep to the original shape or angle. The point of the rack hook is
always broader than the rack, and the mark worn in it will be about
the middle of the thickness; so enough will be left to show what the
original shape or angle was.
After cleaning, particularly if it be French, look for dots on the
rims of the wheels, and for pinions with one end of one leaf filed off
slantingly. When putting it together, place the pin wheel (that is the
one with the pins) and the pinion it engages with so that the leaf of
the pinion (which you will find filed slanting at one extremity) enters
between the two teeth of the wheel, opposite which you will find a
countersunk mark, on the side of the wheel. See also that the gathering
pallet, F, which lifts the rack, does so at the same time that the gong
hammer falls. Then place the hour and minute wheels and cannon pinion
so that the countersunk marks on each line with each other. Neglect
of the marks on a marked train generally means that you will have to
take the clock down again and set it up properly before it will run;
therefore pay attention to these marks the first time.
QUARTER CHIMING SNAIL STRIKES.—Fig. 107 shows the counting mechanism
and trains of an English, fusee, quarter-strike work. The time train
occupies the center, the hour striking train the left and the chiming
train the right. All the train wheels are between the plates and are
dotted in as in Fig. 104, while the counting mechanism is on the front
plate, behind the dial and is drawn in full lines, to show that it is
outside.
GOING TRAIN.
Fusee Wheel 96
Pinion 8
Center Wheel 84
Pinion 7
Third Wheel 78
Pinion 7
STRIKING TRAIN.
Fusee Wheel 84
Pinion 8
Pin Wheel, 8 pins in Pin Wheel 64
Pinion 8
Pallet Wheel 70
Pinion 7
Warning Wheel 60
Fly Pinion 7
CHIMING TRAIN.
Fusee Wheel 100
Pinion 8
Second Wheel 80
Pinion 8
Pallet Wheel 64
Pinion 8
Chiming Wheel 40
Warning Wheel 50
Fly Pinion 8
The reader will see a marked resemblance between the hour and time
trains of Fig. 104 and the same trains of Fig. 107. The hour rack hook
in 107, however, is hung from the center and the hour warning lever is
raised by a spring instead of a lifting piece.
The minute wheel of Fig. 107 carries a snail of four steps,
corresponding to the four teeth of the quarter rack, and the tail of
the quarter rack is bent upwards towards the rack, to engage with the
quarter snail. The quarter rack carries a pin which projects on both
sides of the rack; one side of this pin stops the tail of the quarter
gathering pallet and therefore locks the train as fully described in
Fig. 104. The other side of the same pin acts on the tail of the hour
warning lever, so that whenever the quarter rack falls the hour warning
lever is released and its spring moves it into the path of the hour
warning pin. This goes on whether the hour rack hook is released or
not. Behind the quarter snail, there are four pins in the minute wheel;
these pins raise the quarter lifting piece, which raises the quarter
rack hook and the quarter warning lever at the same time, thus warning
and dropping the quarter rack; as soon as the lifting piece drops, the
warning lever and rack hook are released and the quarter train starts.
[Illustration: Fig. 107. Quarter chiming snail strike, English fusee
movement.]
[Illustration: Fig. 108. Eight day snail half hour strike, French
system, striking train locked.]
One, two, three, or four quarters are chimed according to the position
of the quarter snail, which turns with the minute wheel. At the time
for striking the hour (when the quarter rack is allowed to fall its
greatest distance), the pin in it falls against the bent arm of the
hour rack hook, and releases the hour rack and hour warning lever. As
the last tooth of the quarter rack is gathered up, the pin in the
quarter rack pulls over the hour warning lever, and lets off the hour
striking train. The position of the pieces in the drawing is as they
would be directly after the hour was struck.
Figs. 108, 109 and 110 are three views of the New Haven eight-day snail
strike, which is on the French system. As nearly all American strikes
utilize this system and the work is between the plates, this may be
considered a typical American snail strike.
As will be seen in Fig. 108, by the two pins at the center arbor,
immediately behind the snail, this is a half-hour strike; and as the
rack hook has for its lower step a little more than twice the depth of
the other steps in the snail, it will readily be perceived that this
rack hook may be pushed almost out and thus release the train without
dropping the rack. This is the method pursued in striking half hours.
Figs. 109 and 110 show the parts more clearly than in 108. They are
drawn a little larger than actual size and we will discover that the
rack is the only portion of this system that works by gravity, all the
others being spring operated. We see here the pins J K, which are used
to push out the lever M sufficiently far so that the upper portion,
which is bent at right angles to form a stop, will free the warning pin
O and allow the train to run. The rack hook and the locking lever L are
mounted on the same arbor and are kept in position by a coiled spring
on the arbor until they are pushed out by the lower projection at the
upper end of M for either the half-hour or hour strike.
As shown in Fig. 109, the lever M and the rack hook are pushed out by
J far enough to pass the warning pin O and to unlock the train, which
is normally locked by the pin N and the lever L. G is the gathering
pallet, which is a long pin in a lantern pinion as in the ordinary
count wheel strike. H is the hammer tail and P the pin wheel; R is the
rack and T the rack tail. The rack arm is curved to pass the center
arbor when dropping for twelve and the rack tail is bent toward the
teeth in order that it may admit of a longer rack in a small movement,
thus permitting of a large snail and consequently less liability of
disarrangement. The same necessity of the proper adjustment of the rack
tail T with the snail exists as has already been spoken of in regard to
the English form of the snail strike.
In Fig. 110 will be seen the rack dropped clear with the tail resting
clear of the snail at one stroke from the snail. In other words, the
train is now in position to give eleven more strokes, having struck the
first stroke of twelve. By comparison with Fig. 109, it will be seen
that the spring actuated arm M has been thrown forward so that its dog
is resting on the center arbor, after having been released from the
hour pin K. This holds M out of the way of the warning pin O and the
rack hook and allows the parts to operate as fully described with the
English rack.
The gathering pallet G must have as many teeth as there are teeth
between the pins in the pin wheel P. The train is locked by L coming in
contact with N, the locking pin on the wheel on the same arbor as the
gathering pallet. In setting this train up, it should stop so that the
warning pin O should be near the fly.
As all the parts are operated by springs on the arbor, as shown by the
hammer-spring H, it will be seen that this strike mechanism will work
in any position, while that which is operated by gravity must be kept
upright. A loose fly will cause the clock to strike too fast and may
cause it to strike wrong. Careless adjustment of the rack tail T with
the snail will also induce wrong counting, although this is somewhat
easier to adjust than the English form of strike. The hook should
safely clear the rack teeth just as the gathering pallet G lets go of
a tooth. If attention is paid to this point in adjusting the rack tail
there will generally be little trouble.
[Illustration: Fig. 109. Train about to strike the half hour; the hook
L free of the train, which is held by the warning pin O; one stroke
will be given when M drops.]
The cam bearing the pins J K on the center arbor may be shifted with
a pair of pliers to secure accurate register of hands and strike, as
is the case with most American strikes. In putting in the pin wheel it
should be set so that the pins may have a little run before striking
the hammer tail, as this hammer tail is very short, and if the spring
is strong the pins may not be able to lift the hammer tail without
sufficient run to get the train thoroughly under motion. The half-hour
strike should also be tested so that the pin J will release the warning
pin O from the lever M without releasing the rack hook from the rack,
as shown in Fig. 109. The parts of the train when at rest will be
readily discerned in Fig. 108, where the hook L has locked the train by
the pin N and the freedom between the pins and the hammer tail is about
what it should be.
[Illustration: Fig. 110. Train unlocked and running. Note position of L
and M.]
The relative position of the locking lever L and the rack hook is also
very clearly shown in Fig. 108; that is, when the rack hook is pressed
clear home at the lower notch of the rack, the lever L should safely
lock the train and the lever M be resting with its link against the
center arbor.