PLATES, PIVOTS AND TIME TRAINS.
Before going further with the mechanism of our clocks we will now
consider the means by which the various members are held in their
positions, namely, the plates. Like most other parts of the clock these
have undergone various changes. They have been made of wood, iron and
brass and have varied in shapes and sizes so much that a great deal may
be told concerning the age of a clock by examining the plates.
Most of the wooden clocks had wooden plates. The English and American
movements were simply boards of oak, maple or pear with the holes
drilled and bushed with brass tubes—full plates. The Schwarzwald
movements were generally made with top and bottom boards and
stanchions, mortised in between them to carry the trains, which were
always straight-line trains. The rear stanchions were glued in position
and the front ones fitted friction-tight, so that they could be removed
in taking down the clock. This gave a certain convenience in repairing,
as, for instance, the center (time) train could be taken down without
disturbing the hour or quarter trains, or vice versa. Various attempts
have been made since to retain their convenience with brass plates, but
it has always added so much to the cost of manufacture that it had to
be abandoned.
The older plates were cast, smoothed and then hammered to compact the
metal. The modern plate is rolled much harder and stiffer and it may
consequently be much thinner than was formerly necessary. The proper
thickness of a plate depends entirely upon its use. Where the movement
rests upon a seat board in the case and carries the weight of a heavy
pendulum attached to one of the plates they must be made stiff enough
to furnish a rigid support for the pendulum, and we find them thick,
heavy and with large pillars, well supported at the corners, so as to
be very stiff and solid. An example of this may be seen in that class
of regulators which carry the pendulum on the movement. Where the
pendulum is light the plates may therefore be thin, as the only other
reason necessary for thickness is that they may provide a proper length
of bearing for the pivots, plus the necessary countersinking to retain
the oil.
In heavy machinery it is unusual to provide a length of box or journal
bearing of more than three times the diameter of the journal. In most
cases a length of twice the diameter is more than sufficient; in clock
and other light work a “square” bearing is enough; that is one in
which the length is equal to the diameter. In clocks the pivots are of
various sizes and so an average must be found. This is accomplished
by using a plate thick enough to furnish a proper bearing for the
larger pivots and countersinking the pivot holes for the smaller pivots
until a square bearing is obtained. This countersinking is shaped in
such a manner as to retain the oil and as more of it is done on the
smaller and faster moving pivots, where there is the greatest need of
lubrication, the arrangement works out very nicely, and it will be seen
that with all the lighter clocks very thin plates may be employed while
still retaining a proper length of bearing in the pivot holes.
The side shake for pivots should be from .002 to .004 of an inch; the
latter figure is seldom exceeded except in cuckoos and other clocks
having exposed weights and pendulums. Here much greater freedom is
necessary as the movement is exposed to dust which enters freely at the
holes for pendulum and weight chains, so that such a clock would stop
if given the ordinary amount of side shake.
We are afraid that many manufacturers of the ordinary American clock
aim to use as thin brass as possible for plates without paying too much
attention to the length of bearing. If a hole is countersunk it will
retain the oil when a flat surface will not. The idea of countersinking
to obtain a shorter bearing will apply better to the fine clocks than
to the ordinary. In ordinary clocks the pivots must be longer than
the thickness of the plates for the reason that freight is handled so
roughly that short pivots will pop out of the plates and cause a lot of
damage, provided the springs are wound when the rough handling occurs.
It will be seen by reference to Chapter VII (the mechanical elements
of gearing), Figs. 21 to 25, that a wheel and pinion are merely a
collection of levers adapted to continuous work, that the teeth may
be regarded as separate levers coming into contact with each other in
succession; this brings up two points. The first is necessarily the
relative proportions of those levers, as upon these will depend the
power and speed of the motion produced by their action. The second
is the shapes and sizes of the ends of our levers so that they shall
perform their work with as little friction and loss of power as
possible.
TO GET CENTER DISTANCES.—As the radii and circumferences of circles are
proportional, it follows that the lengths of our radii are merely the
lengths of our levers (See Fig. 24), and that the two combined (the
radius of the wheel, plus that of the pinion) will be the distance at
which we must pivot our levers (our staffs or arbors of our wheels)
in order to maintain the desired proportions of their revolution.
Consequently we can work this rule backwards or forwards.
For instance if we have a wheel and pinion which must work together in
the proportion of 7½ to 1; then 7½ + 1 = 8½ and if we divide the space
between centers into 8½ spaces we will have one of these spaces for
the radius of the _pitch circle_ of the pinion and 7½ for the _pitch
circle_ of the wheel, Fig. 65. This is independent of the number of
teeth so long as the _proportions_ be observed; thus our pinion may
have eight teeth and the wheel sixty, 60 ÷ 8 = 7.5, or 75 ÷ 10 = 7.5,
or 90 ÷ 12 = 7.5, or any other combination of teeth which will make the
correct proportion between them and the center distances. The reason is
that the teeth are added to the wheel to prevent slipping, and if they
did not agree with each other and also with the proportionate distance
between centers there would be trouble, because the desired proportion
could not be maintained.
Now we can also work this rule backwards. Say we have a wheel of 80
teeth and the pinion has 10 leaves but they do not work together
well in the clock. Tried in the depthing tool they work smoothly.
80 ÷ 10 = 8, consequently our center distance must be as 8 and 1.
8 + 1 = 9; the wheel must have 8 parts and the pinion 1 part of the
radius of the pitch circle of the wheel. Measure carefully the diameter
of the pitch circle of the wheel; half of that is the pitch radius, and
nine-eighths of the pitch radius is the proper center distance for that
wheel and pinion.
Say we have lost a wheel; the pinion has 12 teeth and we know the arbor
should go seven and one-half times to one of the missing wheel; we
have our center distances established by the pivot holes which are not
worn; what size should the wheel be and how many teeth should it have?
12 × 7.5 = 90, the number of teeth necessary to contain the teeth of
the pinion 7.5 times. 7.5 + 1 = 8.5, the sum of the center distances;
the pitch radius of the pinion can be closely measured; then 7.5 times
that is the pitch radius of the missing wheel of 90 teeth. Other
illustrations with other proportions could be added indefinitely but we
have, we think, said enough to make this point clear.
[Illustration: Fig. 65. Spacing off center distances; c, center of
wheel; e, pitch circle; d, dedendum; b, addendum; a, center of pinion.]
CONVERSION OF NUMBERS.—There is one other point which sometimes
troubles the student who attempts to follow the expositions of this
subject by learned writers and that is the fact that a mathematician
will take a totally different set of numbers for his examples, without
explaining why. If you don’t know why you get confused and fail to
follow him. It is done to avoid the use of cumbersome fractions. To use
a homely illustration: Say we have one foot, six inches for our wheel
radius and 4.5 inches for our pinion radius. If we turn the foot into
inches we have 18 inches. 18 ÷ 4.5 = 4, which is simpler to work with.
Now the same thing can be done with fractions. In the above instance
we got rid of our larger unit (the foot) by turning it into smaller
units (inches) so that we had only one kind of units to work with. The
same thing can be done with fractions; for instance, in the previous
example we can get rid of our mixed numbers by turning everything
into fractions. Eighteen inches equals 36 halves and 4.5 equals 9
halves; then 36 ÷ 9 = 4. This is called the conversion of numbers and
is done to simplify operations. For instance in watch work we may find
it convenient to turn all our figures into thousands of a millimeter, if
we are using a millimeter gauge. Say we have the proportions of 7.5 to
1 to maintain, then turning all into halves, 7½ × 2 = 15 and 1 × 2 = 2.
15 + 2 = 17 parts for our center distance, of which the pitch radius of
the pinion takes 2 parts and that of the wheel 15.
THE SHAPES OF THE TEETH.—The second part of our problem, as stated
above, is the shapes of the ends of our levers or the teeth of our
wheels, and here the first consideration which strikes us is that the
teeth of the wheels approach each other until they meet; roll or slide
upon each other until they pass the line of centers and then are drawn
apart. A moment’s consideration will show that as the teeth are longer
than the distance between centers and are securely held from slipping
at their centers, the outer ends _must_ either roll or slide after they
come in contact and that this action will be much more severe while
they are being driven towards each other than when they are being drawn
apart after passing the line of centers. This is why the _engaging_
friction is more damaging than the _disengaging_ friction and it is
this _butting_ action which uses up the power if our teeth are not
properly shaped or the center distances not right. Generally speaking
this butting causes serious loss of power and cutting of the teeth when
the pivot holes are worn or the pivots cut, so that there is a side
shake of half the diameter of the pivots, and bushing or closing the
holes, or new and larger pivots are then necessary. This is for common
work. For fine work the center distances should be restored long before
the wear has reached this point.
If we take two circular pieces of any material of different diameters
and arrange them so that each can revolve around its center with their
edges in contact, then apply power to the larger of the two, we find
that as it revolves its motion is imparted to the other, which revolves
in the opposite direction, and, if there is no slipping between the
two surfaces, with a velocity as much greater than that of the larger
disc as its diameter is exceeded by that of the larger one. We have,
then, an illustration of the action of a wheel and pinion as used in
timepieces and other mechanisms. It would be impossible, however, to
prevent slipping of these smooth surfaces on each other so that power
(or motion) would be transmitted by them very irregularly. They simply
represent the “pitch” circles or circles of contact of these two
mobiles. If now we divide these two discs into teeth so spaced that
the teeth of one will pass freely into the spaces of the other and add
such an amount to the diameter of the larger that the points of its
teeth extend inside the pitch circle of the smaller, a distance equal
to about 1⅛ times the width of one of its teeth, and to the smaller so
that its teeth extend inside the larger one-half the width of a tooth,
the ends of the teeth being rounded so as not to catch on each other
and the centers of revolution being kept the same distance apart, on
applying power to the larger of the two it will be set in motion and
this motion will be imparted to the smaller one. Both will continue to
move with the same relative velocity as long as sufficient power is
applied. Other pairs of mobiles may be added to these to infinity, each
addition requiring the application of increased power to keep it in
motion.
These pairs of mobiles as applied to the construction of timepieces are
usually very unequal in size and the larger is designated as a “wheel”
while the smaller, if having less than 20 teeth, is called a “pinion”
and its teeth “leaves.” Now while we have established the principle of
a train of wheels as used in various mechanisms, our gearing is very
defective, for while continuous motion may be transmitted through such
a train, we will find that to do so requires the application of an
impelling force far in excess of what should be required to overcome
the inertia of the mobiles, and the amount of friction unavoidable in a
mechanism where some of the parts move in contact with others.
This excess of power is used in overcoming a friction caused by
improperly shaped teeth, or when formed thus the teeth of the wheel
come in contact with those of the pinion and begin driving at a point
in front of what is known as the “line of centers,” i. e., a line drawn
through the centers of revolution of both mobiles, and as their motion
continues the driven tooth slides on the one impelling it toward the
center of the wheel. When this line is reached the action is reversed
and the point of the driving tooth begins sliding on the pinion leaf
in a direction away from the center of the pinion, which action is
continued until a point is reached where the straight face of the leaf
is on a line tangential to the circumference of the wheel at the point
of the tooth. It then slips off the tooth, and the driving is taken up
on another leaf by the next succeeding tooth. The sliding action which
takes place in front of the line of centers is called “engaging,” that
after this line has been passed “disengaging” friction.
Now we know that in the construction of timepieces, friction and
excessive motive power are two of the most potent factors in producing
disturbances in the rate, and that, while some friction is unavoidable
in any mechanism, that which we have just described may be almost
entirely done away with. Let us examine carefully the action of a
wheel and pinion, and we will see that only that part of the wheel
tooth is used, which is outside the pitch circle, while the portion
of the pinion leaf on which it acts is the straight face lying inside
this circle, therefore it is to giving a correct shape to these parts
we must devote our attention. If we form our pinion leaves so that
the portion of the leaf inside the pitch circle is a straight line
pointing to the center, and give that portion of the wheel tooth lying
outside the pitch circle (called the addenda, or ogive of the tooth)
such a degree of curvature that during its entire action the straight
face of the leaf will form a tangent to that point of the curve which
it touches, no sliding action whatever will take place after the line
of centers is passed, and if our pinion has ten or more leaves, the
“addenda” of the wheel is of proper height, and the leaves of the
pinion are not too thick, there will be no contact in front of the line
of centers. With such a depth the only friction would be from a slight
adhesion of the surfaces in contact, a factor too small to be taken
into consideration.
[Illustration: Showing that a hypocycloid of half the pitch circle is a
straight line.]
[Illustration: Generating an epicycloid curve for a cut pinion. D,
generating circle. Dotted line epicycloid curve. Note how the shape
varies with the thickness of the tooth.]
Here, then, we have an ideal depth. How shall we obtain the same
results in practice? It is comparatively an easy matter to so shape
our cutters that the straight faces of our pinion leaves will be
straight lines pointing to the center, but to secure just the proper
curve for the addenda of our wheel teeth requires rather a more
complicated manipulation. This curve does not form a segment of a
circle, for it has no two radii of equal length, and if continued
would form, not a circle, but a spiral. To generate this curve, we
will cut from cardboard, wood, or sheet metal, a segment of a circle
having a _radius_ equal to that of our _wheel_, on the pitch circle,
and a smaller circle whose _diameter_ is equal to the _radius_ of the
_pinion_, on the pitch circle. To the edge of the small circle we will
attach a pencil or metal point so that it will trace a fine mark. Now
we lay our segment flat on a piece of drawing paper, or sheet metal and
cause the small circle to revolve around its edge without slipping. We
find that the point in the edge of the small circle has traced a series
of curves around the edge of the segment.
These curves are called “epicycloids,” and have the peculiar property
that if a line be drawn through the generating point and the point of
contact of the two circles, this will always be at right angles to a
tangent of the curve at its point of intersection. It is this property
to which it owes its value as a shape for the acting surface of a wheel
tooth, for it is owing to this that a tooth whose acting surface is
bounded by such a curve can impel a pinion leaf through the entire lead
with little sliding action between the two surfaces. This, then, is the
curve on which we will form the addenda of our wheel teeth.
In Fig. 66, the wheel has a radius of fifteen inches and the pinion
a radius of one and one-half, and these two measurements are to be
added together to find the distance apart of the two wheels; 16.5
inches is then the distance that the centers of revolution are apart
of the wheels. Now, the teeth and leaves jointly act on one another to
maintain a sure and equable relative revolution of the pair.
In Fig. 66, the pinion has its leaves radial to the center, inside of
the pitch line D, and the ends of the leaves, or those parts outside
of the pitch line, are a half circle, and serve no purpose until the
depthings are changed by wear, as they never come in contact with the
wheel; the wheel teeth only touch the radial part of the pinion and
that occurs wholly within the pitch line. So in all pinions above 10
leaves in number the addendum or curve is a thing of no moment, except
as it may be too large or too long. In many large pieces of machinery
the pinions, or small driven wheels, have no addendum or extension
beyond their pitch diameter and they serve every end just as well. In
watches there is so much space or shake allowed between the teeth and
pinions that the end of a leaf becomes a necessity to guard against the
pinion’s recoiling out of time and striking its sharp corner against
the wheel teeth and so marring or cutting them. In a similar pair
of wheels in machinery there are very close fits used and the shake
between teeth is very slight and does not allow of recoil, butting, or
“running out of time.”
Running out of time is the sudden stopping and setting back of a pinion
against the opposite tooth from the one just in contact or propelling.
This, with pinions of suppressed ends, is a fault and it is averted by
maintaining the ends.
The wheel tooth drives the pinion by coming in contact with the
straight flank of the leaf at the line of centers, that is a line drawn
through the centers of the two wheels; centers of revolution.
The curve or end of the wheel tooth outside of the pitch line is the
only part of the tooth that ever touches the pinion and it is the
part under friction from pressure and slipping. At the first point of
contact the tooth drives the pinion with the greatest force, as it is
then using the shortest leverage it has and is pressing on the longest
lever of the leaf. As this action proceeds, the tooth is acted on by
the pinion leaf farther out on the curve of the wheel tooth, thus
lengthening the lever of the wheel and at the same time the tooth thus
acts nearer to the center of the pinion by touching the leaf nearer its
center of revolution.
By these joint actions it will appear that the wheel first drives with
the greatest force and then as its own leverage lengthens and its force
consequently decreases, it acts on a shorter leverage of the pinion,
as the end of a tooth is nearer to the center of the pinion, or on the
shortest pinion leverage, just as the tooth is about ceasing to act.
The action is thus shown from the above to be a variable one, which
starts with a maximum of force and ends with a minimum. Practically
the variable force in a train is not recognized in the escapement, as
the other wheels and pinions making up the train are also in the same
relations of maximum and minimum forces at the same time, and thus this
theoretical and virtual variability of train force is to a great extent
neutralized at the active or escaping end of the movement.
There is another action between the tooth and leaf that is not easy
to explain without somewhat elaborate sketches of the acting parts,
and as this is not consistent with such an article, we may dismiss
it, and merely state that it is the one of maintaining the relative
angular velocities of the two wheels at all times during their joint
revolutions.
In Fig. 66 will be seen the teeth of the wheel, their heights, widths
and spacing, and the epicycloidal curves. Also the same features of
the pinion’s construction. The curve on the end of the wheel teeth is
the only curve in action during the rotation between wheel and pinion.
Each flank (both teeth and leaves) is a straight line to the center
of each. A tooth is composed of two members—the pillar or body of the
tooth inside of the pitch line and the cycloid or curve, wholly outside
of this line. The pinion also has two members, the radial flank wholly
inside of the pitch line, and its addendum or circle outside of this
line.
[Illustration: Fig. 66.]
In Fig. 66 will be seen a tooth on the line of centers A B, just coming
in action against the pinion’s flank and also one just ceasing action.
It will be seen that the tooth just entering is in contact at the joint
pitches, or radii, of the two wheels, and that when the tooth has run
its course and ceased to act, that it will be represented by tooth 2.
Then the exit contact will be at the dotted line _o o_. From this may
be seen just how far the tooth has, in its excursion, shoved along
the leaf of the pinion and by the distance the line _o o_, is from
the wheel’s pitch line G, at this tooth. No. 2, is shown the extent
of contact of the wheel tooth. By these dotted lines, then, it may
be seen that the tooth has been under friction for nearly its whole
curve’s length, while the pinion’s flank will have been under friction
contact for less than half this distance. In brief, the tooth has moved
about ⁸⁰/₁₀₀ of its curved surface along the straight flank .35 of
the surface of the pinion leaf. From this relative frictional surface
may be seen the reason why a pinion is apt to be pitted by the wheel
teeth and cut away. In any case it shows the relation between the two
friction surfaces. In part a wheel tooth rolls as well as slides along
the leaf, but whatever rolling there may be, the pinion is also equally
favored by the same action, which leaves the proportions of individual
friction still the same.
In Fig. 66 may be seen the spaces of the teeth and pinion. The teeth
are apart, equal to their own width and the depths of the spaces are
the same measurement of their width—that is, the tooth (inside of the
pitch line) is a pillar as wide as it is high and a space between two
teeth is of like proportions and extent of surface. The depth of a
space between two teeth is only for clearance and may be made much
less, as may be seen by the pinion leaf, as the end of the circle does
not come half way to the bottom of a space.
The dotted line, _o o_, shows the point at which the tooth comes out
of action and the pointed end outside of this line might be cut off
without interfering with any function of the tooth. They generally are
rounded off in common clock work.
The pinion is 3 inches diameter and is divided into twelve spaces
and twelve leaves; each leaf is two-fifths of the width of a space
and tooth. That is one-twelfth of the circumference of the pinion is
divided into five equal parts and the leaf occupies two and a space
three of these parts. The space must be greater than the width of a
leaf, or the end of a leaf would come in contact with a tooth before
the line of centers and cause a jamming and butting action. Also the
space is needed for dirt clearance. As watch trains actuated by a
spring do not have any reserve force there must be allowance made for
obstructions between the teeth of a train and so a large latitude is
allowed in this respect, more than in any machinery of large caliber.
As will be seen by Fig. 66, the spans between the leaves are deep, much
more so than is really necessary, and a space at O C shows the bottom
of a space, cut on a circle which strengthens a leaf at its root and is
the best practice.
Having determined the form of our curve, our next step will be to get
the proper proportions. Saunier recommends that in all cases tooth
and space should be of equal width, but a more modern practice is
to make the space slightly wider, say one-tenth where the curve is
epicycloidal. When the teeth are cut with the ordinary Swiss cutters,
which, of course, cannot be epicycloidal, it is best to make the
spaces one-seventh wider than the tooth. This proportion will be
correct except in the case of a ten-leaf pinion, when, if we wish to
be sure the driving will begin on the line of centers, the teeth must
be as wide as the spaces; but in this case the pinion leaf is made
proportionately thinner, so that the requisite freedom is thus obtained.
The height of the addenda of the wheel teeth above the pitch circle is
usually given as one and one-eighth times the width of a tooth. While
this is approximately correct, it is not entirely so, for the reason
that as we use a circle whose diameter is equal to the pitch radius of
the pinion for generating the curve, the height of the addenda would be
different on the same wheel for each different numbered pinion. So that
if a wheel of 60 were cut to drive a pinion of 8, the curve of this
tooth would be found too flat if used to drive a pinion of 10. Now,
since the pitch diameter of the pinion is to the pitch diameter of the
wheel as the number of leaves in the pinion are to the number of teeth
in the wheel, in order to secure perfect teeth: we must adopt for the
height of the addenda a certain proportion of the radius or diameter of
the pinion it is to drive, this proportion depending on the number of
leaves in the pinion.
A careful study of the experiments on this subject with models of
depths constructed on a large scale, shows that the proportions given
below come the nearest to perfection.
When the pinion has six leaves the spaces should be twice the width
of the leaves and the depth of the space a little more than one-half
the total radius of the pinion. The addenda of the pinion should be
rounded, and should extend outside the pitch circle a distance equal
to about one-half the width of a leaf. The addenda of the wheel teeth
should be epicycloidal in form and should extend outside the pitch
circle a distance equal to five-twelfths of the pitch radius of the
pinion.
With these proportions, the tooth will begin driving when one-half
the thickness of a leaf is in front of the line of centers, and there
will be engaging friction from this point until the line of centers is
reached.
This cannot be avoided with low numbered pinions without introducing
a train of evils more productive of faulty action than the one we are
trying to overcome. There will be no disengaging friction.
When a pinion of seven is used, the spaces of the pinion should
be twice the width of the leaves, and the depth of a space about
three-fifths of the total radius of the pinion. The addenda of the
pinion leaves should be rounded, and should extend outside the pitch
circle about one-half the width of a leaf. The addenda of the wheel
teeth should be epicycloidal, and the height of each tooth above the
pitch circle equal to two-fifths of the pitch radius of the pinion.
There is less engaging friction when a pinion of seven is used than
with one of six, as the driving does not begin until two-thirds of the
leaf is past the line of centers. There is no disengaging friction.
With an eight-leaf pinion the space should be twice as wide as the
leaf, and the depth of a space about one-half the total radius of the
pinion. The addenda of the pinion leaves should be rounded and about
one-half the width of a leaf outside the pitch circle. The addenda of
the wheel teeth should be epicycloidal, and the height of each tooth
above the pitch circle equal to seven-twentieths of the pitch radius of
the pinion.
With a pinion of eight there is still less engaging friction than with
one of seven, as three-quarters of the width of a leaf is past the
line of centers when the driving begins. As there is no disengaging
friction, a pinion of this number makes a very satisfactory depth.
A pinion with nine leaves is sometimes, though seldom, used. It should
have the spaces twice the width of the leaves, and the depth of a space
one-half the total radius. The addenda should be rounded, and its
height above the pitch circle equal to one-half the width of the leaf.
The addenda of the wheel teeth should be epicycloidal, and the height
of each tooth above the pitch circle equal to three-sevenths of the
total radius of the pinion. With this pinion the driving begins very
near the line of centers, only about one-fifth of the width of a leaf
being in front of the line.
A pinion of ten leaves is the lowest number with which we can entirely
eliminate engaging friction, and to do so in this case the proper
proportions must be rigidly adhered to. The spaces on the pinion must
be a little more than twice as wide as a leaf; a leaf and space will
occupy 36° of arc; of this 11° should be taken for the leaf and 25°
for the space. The addenda should be rounded and should extend about
half the width of a leaf outside the pitch circle. The depth of a space
should be equal to about one-half the total radius. For the wheel, the
teeth should be equal in width to the spaces, the addenda epicycloidal
in form, and the height of each tooth above the pitch circle, equal to
two-fifths the pitch radius of the pinion.
A pinion having eleven leaves would give a better depth, theoretically,
than one of ten, as the leaves need not be made quite so thin to ensure
its not coming in action in front of the line of centers. It is seldom
seen in watch or clock work, but if needed the same proportions should
be used as with one of ten, except that the leaves may be made a little
thicker in proportion to the spaces.
A pinion having twelve leaves is the lowest number with which we can
secure a theoretically perfect action, without sacrificing the strength
of the leaves or the requisite freedom in the depths. In this pinion,
the leaf should be to the space as two to three, that is, we divide the
arc of the circumference needed for a leaf and space into five equal
parts, and take two of these parts for the leaf, and three for the
space; depth of the space should be about one-half the total radius.
The addenda of the wheel teeth should be epicycloidal, and the height
of each tooth above the pitch line equal to two-sevenths the pitch
radius of the pinion.
As the number of leaves is increased up to twenty, the width of the
space should be decreased, until when this number is reached the space
should be one-seventh wider than the leaf. As these numbers are used
chiefly for winding wheels in watches, where considerable strength is
required, the bottoms of the spaces of both mobiles should be rounded.
CIRCULAR PITCH. DIAMETRAL PITCH.—In large machinery it is usual to take
the circumference and divide by the number of teeth; this is called
the _circular pitch_, or distance from point to point of the teeth, and
is useful for describing teeth to be cut out as patterns for casting.
But for all small wheels it is more convenient to take the diameter
and divide by the number of teeth. This is called the _diametral
pitch_, and when the diameter of a wheel or pinion which is intended
to work into it is desired, such diameter bears the same ratio or
proportion as the number required. Both diameters are for their pitch
circles. As the teeth of each wheel project from the pitch circle and
enter into the other, an addition of corresponding amount is made to
each wheel; this is called the _addendum_. As the size of a tooth of
the wheel and of a tooth of the pinion are the same, the amount of
the addendum is equal for both; consequently the outside diameter of
the smaller wheel or pinion will be greater than the arithmetical
proportion between the pitch circles. As the diameters are measured
presumably in inches or parts of an inch, the number of a wheel of
given size is divided by the diameter, which gives the number of teeth
to each inch of diameter, and is called the _diametral pitch_. In all
newly-designed machinery a whole number is used and the sizes of the
wheels calculated accordingly, but when, as in repairing, a wheel of
any size has any number of teeth, the diametral number may have an
additional fraction, which does not affect the principle but gives a
little more trouble in calculation. Take for example a clock main wheel
and center pinion: Assuming the wheel to be exactly three inches in
diameter at the pitch line, and to have ninety-six teeth, the result
will be 96 ÷ 3 = 32, or 32 teeth to each inch of diameter, and would
be called _32 pitch_. A pinion of 8 to gear with this wheel would
have a diameter at the pitch line of 8 of these thirty-seconds of an
inch or ⁸/₃₂ of an inch. But possibly the wheel might not be of such
an easily manageable size. It might, say, be 3.25 inches, in which
case, 96 being the number of the wheel and 8 of the pinion, the ratio
is ⁸/₉₆ or ¹/₁₂, so ¹/₁₂ of 3.25 = 0.270, the pitch diameter of the
pinion. These two examples are given to indicate alternative methods,
the most convenient of which may be used. After arriving at the true
pitch diameters the matter of the addendum arises, and it is for this
that the diametral number is specially useful, as in every case when
figuring by this system, whatever the number of a wheel or pinion,
two of the pitch numbers are to be added. Thus with the 32 pitch, the
outside diameter of the wheel will be 3 in. + ²/₃₂, and if the pinion
⁸/₃₂ + ²/₃₂ = ¹⁰/₃₂. With the other method the same exactness is more
difficult of attainment, but for practical purposes it will be near
enough if we use ²/₃₀ of an inch for the addendum, when the result
will be 3.25 + ²/₃₀ or 3¼ + ²/₃₀ = 3⅓; in. nearly and the pinion
0.270 + ²/₃₀ = 0.270 + .0666 = 0.3366; or to work by ⅓ of an inch is
near enough, giving the outside diameter of the pinion a small amount
less than the theoretical, which is always advisable for pinions which
are to be driven.
We represent by Figs. 67 to 71 a wheel of sixty teeth gearing with a
pinion of six leaves. The wheel, whose pitch diameter is represented
by the line mm is the same in each figure. The pinion, which has for
its pitch diameter the line kk, is in Fig. 67, of a size proportioned
to that of the wheel, and its center is placed at the proper distance;
that is to say, the two pitch diameters are tangential.
In Fig. 68 the same pinion, of the proper size, has its center too far
off; the depthing is too shallow. In Fig. 69 it is too deep. Figs. 70
and 71 represent gearing in which the pitch circles are in contact, as
the theory requires, but the size of the pinions is incorrect. If the
wheels and pinion actuated each other by simple contact the velocity of
the pinion with reference to that of the wheel would not be absolutely
the same; but the ratio of the teeth being the same, the same ratio of
motion obtains in practice, and there is necessarily bad working of the
teeth with the leaves.
We will observe what passes in each of these cases, and refer to the
suitable remedies for obtaining a passable depthing and a comparatively
good rate, without the necessity of repairs at a cost out of all
proportion with the value of the article repaired.
[Illustration: Fig. 67.]
Fig. 67 represents gearing of which the wheel and pinion are well
proportioned and at the proper distance from each other. Its movement
is smooth, but it has little drop or none at all. By examining the
teeth h, h′, of the wheel, it is seen that they are larger than the
interval between them. With a cutter FF, introduced between the teeth,
they are reduced at d, d′, which gives the necessary drop without
changing the functions, since the pitch circles mm and kk have not been
modified. The drop, the play between the tooth d′ and the leaf a, is
sufficiently increased for the working of the gearing with safety.
We have the same pair in Fig. 68, but here their pitch circles do not
touch; the depthing is too shallow. The drop is too great and butting
is produced between the tooth h and the leaf r, which can be readily
felt. The remedy is in changing the center distance, by closing the
holes, if worn, or moving one nearer the other. But in an ordinary
clock this wheel may be replaced with a larger one, whose pitch circle
reaches to e. The proportions of the pair are modified, but not
sufficiently to produce inconvenience.
[Illustration: Fig. 68.]
It may also answer to stretch the wheel, if it is thick enough to be
sufficiently increased in size. A cutter should then be selected for
rounding-up which will allow the full width to the tooth as at p;
but if it is not possible to enlarge the wheel enough, a little of
the width of the teeth may be taken off, as is seen at h, which will
diminish the butting with the leaf r.
Too great depthing, Fig. 69, can generally be recognized by the lack
of drop. When the teeth of the wheel are narrow, the drop may appear
to be sufficient. When the train is put in action the depthing that is
too great produces scratching or butting and the ’scape wheel trembles.
This results from the fact that the points of the teeth of the wheel
touch the core of the pinion and cause it to butt against the leaf
following the one engaged, as is visible at r in Fig. 69. It should be
noticed that in this figure the pitch circles mm and kk overlap each
other, instead of being tangential.
[Illustration: Fig. 69.]
[Illustration: Fig. 70.]
To correct this gearing, the cutter should act only on the addenda of
the teeth of the wheel, so as to diminish them and bring the pitch
circle mm to n. The dots in the teeth d, d′, show the corrected
gearing. It is seen that there will be, after this change, the
necessary drop, and that the end of the tooth d′ will not touch the
leaf r.
In the two preceding cases we have considered wheels and pinions of
accurate proportion, and the defects of the gearing proceeding from
the wrong center distances. We will not speak of the gearing in which
the pinion is too small. The only theoretic remedy in this case, as in
that of too large a pinion, is to replace the defective piece; but in
practice, when time and money are to be saved, advantage must be taken,
one way or another, of what is in existence.
The buzzing produced when the train runs in a gearing with too small a
pinion proceeds from the fact that each tooth has a slight drop before
engaging with the corresponding leaf. If we examine Fig. 70, it will
be easy to see how this drop is produced. The wheel revolving in the
direction indicated by the arrow, it can be seen that when the tooth
h leaves the leaf r, the following tooth, p, does not engage with
the corresponding leaf, s; this tooth will therefore have some drop
before reaching the leaf. A friction may even be produced at the end or
addendum of the tooth p against the following leaf v.
To obtain a fair depthing without replacing the pinion, the wheels can
be passed to the rounding-up machine, having a cutter which will take
off only the points of the teeth, as is indicated in the figure; the
result may be observed by the dotted lines. The tooth h being shorter,
it will leave the leaf r of the pinion when the latter is in the dotted
position; that is to say, a little sooner. At this moment the tooth p
is in contact with the leaf s, and there is no risk of friction against
the leaf v. Care must be taken to touch only the addendum of the
tooth so as not to weaken the teeth. The circumference i will be that
of a pinion of accurate size, and if the pinion is replaced, it will
be necessary to diminish the wheel so that its pitch circle shall be
tangential with i.
[Illustration: Fig. 71.]
With too small a pinion a passable gearing can generally be produced.
In any case stoppage can be prevented. This is not so easy when the
pinion is too large. In Fig. 71, the pinion has as its pitch circle the
line k, instead of i, which would be nearer the size with reference to
that of the wheel. This is purposely drawn a little small for clearness
of illustration. The essential defect of such a gearing can be seen;
the butting produced between the tooth p and the leaf s will cause
stoppage. How shall this defect be corrected without replacing the
pinion?
To remedy the butting as far as possible, some watchmakers slope
the teeth of the wheel by decentering the cutter on the rounding-up
machine. At FF the cutter is seen working between the teeth d and d′.
It is evident that when the wheel becomes smaller it is necessary to
stretch it out, and to make use of the cutter afterwards. However,
the most rational method is to leave the teeth straight, and to give
them the slenderest form possible, after having enlarged the wheel or
having replaced it with another. The motive force of the wheel being
sufficiently weak, the size of the teeth may be reduced without fear.
The essential thing is to suppress the butting. Success will be the
easiest when the teeth are thinner.
In conclusion, we recommend verification of all suspected gearings by
the depthing tool, which is easier and surer than by the clock itself.
One can see better by the tool the working of the teeth with the
leaves, and can form a better idea of the defect to be corrected. With
the aid of the illustrations that have been given it can be readily
noticed whether the depthing is too deep or too shallow, or the pinion
too large or too small.
The defects mentioned are of less consequence in a pinion of seven
leaves, and they are corrected more readily. With pinions of higher
numbers the depthings will be smoother, provided sufficient care has
been taken in the choice of the rounding-up cutters.
ROUNDING-UP WHEELS.—It is frequently observed that young watchmakers,
and (regretfully be it said) some of the older and more experienced
ones, are rather careless when fitting wheels on pinions. In many cases
the wheel is simply held in the fingers and the hole opened with a
broach, and in doing this no special care is taken to keep the hole
truly central and of correct size to fit the pinion snugly, and should
it be opened a little too large it is riveted on the pinion whether
concentric or not. Many suppose the rounding-up tool will then make it
correct without further trouble and without sufficient thought of the
irregularities ensuing when using the tool.
To make the subject perfectly clear the subjoined but rather
exaggerated sketch is shown, Fig. 72. Of course, it is seldom required
to round-up a wheel of twelve teeth, and the eccentricity of the wheel
would be hardly as great as shown; nevertheless, assuming such a case
to occur the drawing will exactly indicate the imperfections arising
from the use of a rounding-up tool.
[Illustration: Fig. 72.]
Presuming from the drawing that the wheel, as shown by dotted lines,
had originally been cut with its center at m, but through careless
fitting had been placed on the pinion at o, and consequently is
very much out of round when tested in the calipers, and to correct
this defect it is put in the rounding-up tool. The cutter commences
to remove the metal from tooth 7, it being the highest, next the
neighboring teeth 6 and 8, then 5 and 9, and so on until tooth 1 comes
in contact with the cutter. The wheel is now round. But how about the
size of the teeth and the pitch? The result of the action of the cutter
is shown by the sectionally lined wheel. Many will ask how such, a
result is possible, as the cutter has acted equally upon all the teeth.
Nevertheless, a little study of the action of the rounding-up cutter
will soon make it plain why such faults arise. Naturally the spaces
between the teeth through the action of the cutter will be equal, but
as the cutter is compelled to remove considerable metal from the point
of greatest eccentricity, i. e., at tooth 7 and the adjoining teeth,
to make the wheel round, and the pitch circle being smaller the teeth
become thinner, as the space between the teeth remains the same. At
tooth 1 no metal was removed, consequently it remains in its original
condition. The pitch from each side of tooth 1 becomes less and less to
tooth 7, and the teeth thinner, and the thickest tooth is always found
opposite the thinnest.
In the case of a wheel having a large number of teeth and the
eccentricity of which is small, such faults as described cannot be
readily seen, from the fact that there are many teeth and the slight
change in each is so gradual that the only way to detect the difference
is by comparing opposite teeth. And this eccentricity becomes a serious
matter when there are but few teeth, as before explained, especially
when reducing an escape wheel. The only proper course to pursue is
to cement the wheel on a chuck, by putting it in a step chuck or in
any suitable manner so that it can be trued by its periphery and then
opening the hole truly. This method is followed by all expert workmen.
A closer examination of the drawing teaches us that an eccentric wheel
with pointed teeth—as cycloidal teeth are mostly left in this condition
when placed in the rounding-up tool, will not be made round, because
when the cutter has just pointed the correct tooth (tooth No. 1 in the
drawing) it will necessarily shorten the thinner teeth. Nos. 6, 7, 8,
i. e., the pitch circle will be smaller in diameter. We can, therefore,
understand why the rounding-up tool does not make the wheel round.
As we have before observed, when rounding-up an eccentrically riveted
wheel, the thickest tooth is always opposite the thinnest, but with
a wheel which has been stretched the case is somewhat different.
Most wheels when stretched become angular, as the arcs between the
arms move outward in a greater or less degree, which can be improved
to some extent by carefully hammering the wheel near the arms, but
some inequalities will still remain. In stretching a wheel with five
arms we therefore have five high and as many depressed parts on its
periphery. If this wheel is now rounded-up the five high parts will
contain thinner teeth than the depressed portions. Notwithstanding that
the stretching of wheels, though objectionable, is often unavoidable
on account of the low price of repairs, it certainly ought not to be
overdone. Before placing the wheel in the rounding-up tool it should be
tested in the calipers and the low places carefully stretched so that
the wheel is as nearly round as can be made before the cutter acts upon
it.
It is hardly necessary to mention that the rounding-up tool will not
equalize the teeth of a badly cut wheel, and further should there be a
burr on some of the teeth which has not been removed, the action of the
guide and cutter in entering a space will not move the wheel the same
distance at each tooth, thus producing thick and thin teeth. From what
has been said it would be wrong to conclude that the rounding-up tool
is a useless one; on the contrary, it is a practical and indispensable
tool, but to render good service it must be correctly used.
In the use of the rounding-up tool the following rules are to be
observed:
1. In a new wheel enlarge the hole after truing the
wheel from the outside and stake it concentrically on
its pinion.
2. In a rivetted but untrue wheel, stretch the
deeper portions until it runs true, then reduce it
in the rounding-up tool. The better method is to
remove the wheel from its pinion, bush the hole,
open concentrically with the outside and rivet, as
previously mentioned in a preceding paragraph. But
if the old riveting cannot be turned so that it can
be used again it is best to turn it entirely away,
making the pinion shaft conical towards the pivot,
and after having bushed the wheel, drill a hole the
proper size and drive it on the pinion. The wheel
will be then just as secure as when rivetted, as in
doing the latter the wheel is often distorted. With a
very thin wheel allow the bush to project somewhat,
so that it has a secure hold on the pinion shaft and
cannot work loose.
3. Should there be a feather edge on the teeth,
this should be removed with a scratch brush before
rounding it up, but if for some reason this cannot
well be done, then place the wheel upon the rest
with the feather edge nearest the latter so that the
cutter does not come immediately in contact with
it. If the feather edge is only on one side of the
tooth—which is often the case—place the wheel in
the tool so that the guide will turn it from the
opposite side of the tooth; the guide will now move
the wheel the correct distance for the cutter to act
uniformly. Of course, in every case the guide, cutter
and wheel, must be in correct position to ensure good
work.
4. To obtain a smooth surface on the face of the
teeth a high cutter speed is required, and for this
reason it is advantageous to drive the cutter spindle
by a foot wheel.
MAKING SINGLE PINIONS.—There are two ways of making clock pinions; one
is to take a solid piece of steel of the length and diameter needed
and turn away the surplus material to leave the arbor and the pinion
head of suitable dimensions; the other way is to make the head and
the arbor of separate pieces; the head drilled and fixed on the arbor
by friction. The latter plan saves a lot of work, and the cutting of
the teeth may be easier. One method is as good as the other, as the
force on the train is very slight and the pinion head may be driven
so tightly on the arbor as to be perfectly safe without any other
fastening, provided the arbor is given a very small taper, .001 inch in
four inches. The steel for the arbor may be chosen of such a size as
to require very little turning, and hardened and tempered to a full or
pale blue before commencing turning it, but the piece intended for the
pinion head must be thoroughly annealed, or it may be found impossible
to cut the teeth without destroying a cutter, which, being valuable, is
worth taking care of.
Pinions for ordinary work are not hardened; as they are left soft by
the manufacturers it would be nonsense for the repairer to put in one
hardened pinion in a clock where all the others were soft. Pinions on
fine work are hardened. Turning is done between centers to insure truth.
Before commencing work on the pinion blanks it is advisable to try
the cutters on brass rod, turned to the exact size, and if the rod
is soft enough it will be found that the cutter will make the spaces
before it is hardened, which is a very important advantage, admitting
of correction in the form of the cutter if required; only two or
three teeth need be cut in the brass to enable one to see if they are
suitable, and if found so, or after an alteration of the cutter, the
entire number may be cut round and the brass pinion made use of for
testing its accuracy as to size and shape by laying the wheel along
with it on a flat plate, having studs placed at the proper center
distance. By this means the utmost refinement may be made in the
diameter of the brass pinion, which will then serve as a gauge for the
diameter of the steel pinions, it being recollected, as mentioned in a
previous paragraph, that a slight variation in the diameter of a pinion
may be made to counterbalance a slight deviation from mathematical
accuracy in the form of the wheel teeth, such as is liable to occur
owing to the smallness of the teeth making it impracticable to actually
draw the true curves, the only way of getting them being to draw them
to an enlarged scale on paper, and copy them on the cutter as truly as
possible by the eye.
Supposing the cutter has been properly shaped, hardened and completed
and the steel pinion heads all turned to the diameter of the brass
gauge, the cutting may be proceeded with without fear of spoiling, or
further loss of time which might be spent in cutting the long pinion
leaves; and even what is of more importance in work which does not
allow of any imperfection, removing the temptation, which might be
strong, to let a pinion go, knowing it to be less perfect than it
should be.
Assuming the pinion teeth to be satisfactorily cut, the next operation
will be hardening and tempering. A good way of doing this is to enclose
one at a time in a piece of gas pipe, filling up the space around the
pinion with something to keep the air off the work and prevent any of
the products of combustion attacking the steel and so injuring the
surface. Common soap alone answers the purpose very well, or it may
have powdered charcoal mixed with it; also the addition of common salt
helps to keep the steel clean and white. The heating should be slow,
giving time for the pinion and the outside of the tube to both acquire
the same heat. Over-heating should be carefully avoided, or there will
be scaling of the surfaces, injurious to the steel, and requiring time
and labor to polish off. There is no better way of hardening than by
dipping the pipe with the pinion enclosed in plain cold water, or
if the pinion should drop out of the tube into the water it will do
all the same. To be sure the hardening is satisfactory it will be as
well not to trust to the clean white color likely to result from this
treatment, but try both ends and the center with a file. After all this
has been successfully accomplished the pinions will require tempering,
the long arbors straightening, and the teeth polishing.
The drilled pinion heads, if hardened at all by the method last
mentioned, will, on account of their short lengths, be equally hardened
all over, but if the pinion and arbor should be all in one piece care
will be needed to ensure equal heating all over, or one part may
be burnt and another soft. Also, to guard against bending the long
arbors, the packing in the tube will need to be carefully done, so as
to produce equal pressure all over; otherwise, while the steel is red
hot, and consequently soft enough to bend, even by its own weight, it
may get distorted before dropping in the water. A long thin rod like
this almost invariably bends if heated on an open fire unless equally
supported all along; if hardened so, a little tin tray may be bent up,
filled with powdered charcoal, and the pinion bedded evenly in it.
Either this way or with a tube the long arbor may get bent before being
quenched; but if the arbor, though kept straight up to this point,
should happen to be dropped sideways into the water the side cooled
first would contract most. To avoid this, the arbor should be dropped
endways, as vertically as possible.
TEMPERING THE PINIONS.—For common cheap work the usual and quickest
way is what is called “blazing off.” That is done either by dipping
each piece singly in thick oil and setting the oil on fire, allowing
it to burn away, or placing a number of pieces in a suitably sized
pan, covering with oil, and burning it. The result is the same either
way, the method being simply a matter of convenience regulated by the
number of pieces to be tempered at one time. As the result of blazing
off is to some extent uncertain, and the pinions apt to be too soft,
it will be advisable to adopt the process of bluing, by which the
temper desired may be produced with more accuracy. The first thing
to do will be to clean the surface of the arbor all along on one
side; the pinion head may be left alone. As the pinion head would get
overheated before the arbor had reached the blue color, if the piece
were simply placed on a bluing pan or a lump of hot iron, it will be
necessary to provide a layer of some soft substance to bed the pinion
on; iron, steel or brass filings answer well because the heat is soon
uniformly distributed through the mass, and by judiciously moving the
lamp an equable temper may be got all along, as determined by the
color. There is another and very sure way of getting a uniform temper,
in using which there is no need to polish the arbors. The heat of lead
_at the point of fusion_ happens to be just about the same as that
required for the tempering of this work; so if a ladle full of lead is
available each pinion may be buried in it for a few seconds, holding it
down beneath the molten surface with hot pliers. The temper suitable is
indicated by a pale blue, a little softer than for springs, and a piece
of polished steel set floating on the lead will indicate whether the
heat is suitable; if found too great some tin may be added, which will
cause the metal to melt at a lower temperature. Over-heating the metal
must be avoided: it should go no higher than the bare melting point.
STRAIGHTENING BENT ARBORS.—When all care has been taken in the
hardening, the long pieces of wire are still apt to become bent more
or less, and this is especially the case with solid pinions; so before
proceeding further the pieces must be got true, or as nearly so as
possible, and it will be found impracticable to do this by simple
bending when the steel is tempered. If the piece is placed between
centers in the lathe and rotated slowly, the hollow side will be found;
this side must be kept uppermost while the steel is held on a smooth
anvil, and the pene, or chisel-shaped, end of a small hammer applied
crossways with gentle blows, stepping evenly along so that each portion
of the steel is struck all along the part which is hollow; this will
stretch the hollow side, and, by careful working, trying the truth
from time to time, the piece can be got as true as may be wished, and
probably keep so during the subsequent turning and finishing, though
it is advisable to keep watch on it, and if it shows any tendency to
spring out of truth again, repeat the striking process, which should
always be done gently and in such a way as to show no hammer marks.
Having got the pieces sufficiently true in this way, each arbor may
have a collet of suitable size driven on to it for permanency, and as
the collets will probably be a little out of truth they may have a
finishing cut taken all over them and receive a final polish.
POLISHING.—To polish the steel arbors after turning, a flat metal
polisher, iron or steel, is used; this with emery or oilstone dust and
oil produces a true surface, with a sharp corner at the shoulder; the
polisher will require frequent filing on the flat and the edge to keep
it in shape with a sharp corner, and a grain crossing like the cuts
on a file to hold the grinding material. The polishing of arbors is
not done with the object of making them shine, but to get them smooth
and true, so there is no need of using any finer stuff than emery or
oilstone dust.
An old way to polish the leaves was to use a simple metal polisher of
a suitable thickness, placing the pinion on a cork or piece of wood,
or even holding it in the fingers; working away at a tooth at a time
until a good enough polish was obtained; but this method, while being
satisfactory as to results, was also tedious and very slow. It was in
some cases assisted by having guide pinions fitted tight on one or
both ends of the arbors to prevent rounding of the teeth, the polisher
resting in the guide and the tooth to be polished. On the American
lathes an accessory is provided called a “wig wag.” This is a rod
fastened at one end to a pulley by a crank pin near its circumference;
the pulley being rotated by a belt from the counter shaft pulleys
causes the rod to move rapidly backwards and forwards. On the other
end of the rod a long narrow piece of lead or tin is fixed, the pinion
being fitted by its centres into a simple frame held in the slide rest
so that it can be rotated tooth by tooth; the lead soon gets cut to the
form of the teeth, and the polishing is quickly effected. Another way
is to take soft pine or basswood, shape it roughly to about the form
of space between two teeth and use it as a file, with emery and oil or
oilstone dust. The wood is soon cut to the exact shape of the teeth,
and then makes a quick and perfect job. The pinion is held in the jaws
of the vise and the wooden polisher used as a file with both hands.
Where there is much polishing to do a simple tool, which a workman can
form for himself, produces a result which is all that can be desired.
It consists of an arbor to work between the lathe centres, or a screw
chuck for wood, with a round block of soft wood, of a good diameter,
fixed on it, and turned true and square across; this will get a spiral
groove cut in it by the corners of the pinion leaves. The pinion is
set between centres in a holder in the slide rest, with the holder set
at a slight angle, so that, instead of circular grooves being cut in
the wood a screw will be formed, the angle being found by trial. On
the wood block being rotated and supplied with fine emery the pinion
will be found to rotate, and, being drawn backwards and forwards by the
slide rest, can be polished straight, while the circular action of the
polisher will cause the sides of the pinion leaves to be made quite
smooth and entirely free from ridges.
If it should be desired to face the pinions, like watch pinions, it
may be done in the same way, by cutting hollows so as to leave only a
fine ring round the bottoms of the teeth, and using a hollow polisher
with a flat end held in the fingers while the pinion is rotating. A
common cartridge shell with a hole larger than the arbor drilled in the
center of the head makes a fine polisher for square facing on the ends
of pinions, while a stick of soft wood will readily adapt itself to
moulded ends.
The pinion heads being finished and got quite true, the arbors may
be turned true and polished. It is not advisable to turn the arbors
small; they will be better left thick so as to be stiff and solid, as
the weight so near the center is of no importance, the velocity on the
small circumference in starting and stopping being also inappreciable.
The thickness of the arbors when the pinion heads are drilled is
determined by the necessity of having sufficient body inside the
bottoms of the teeth; but when solid they may with advantage be left
thicker; however, there is no absolute size. The ends on which the
collets for holding the wheels are to be fixed may be turned to the
same taper as the broach which will be used for opening the collet
holes, while the other ends may be straight.
None of the wheels in a fine clock should be riveted to the pinion
heads; even the center wheel, which goes quite up to the pinion head,
is generally fixed on a collet. The collets are made from brass cut
off a round rod, the outside diameters being just inside the edges
of the wheel hubs, and a shoulder turned to fit accurately into the
center hole of each wheel. These collets should first have their holes
broached to fit their arbors, allowing a little for driving on, as they
may be made tight enough in this way without soldering. Be careful to
keep the broach oiled to prevent sticking if you want a smooth round
hole.
The holes in the wheels being made, each collet may be turned to a
little over its final size all over, and then driven on to its place
on the pinion, so that a final turning may be made to ensure exact
truth from the arbors’ own centers. When the collets are thus finished
in their places on the arbors, and the wheels fitted to them, if it
is a fine clock, such as a regulator, a hole may be drilled through
each wheel and its collet to take a screw, the holes in the collet
tapped, the holes in the wheels enlarged to allow the screw to pass
freely through, and a countersink made to each, so that the screws,
when finished, may be flush with the wheels. One hole having been thus
made and the wheel fixed with a screw, the other two holes can be made
so as to be true, which would not be so well accomplished if all the
holes were attempted at once. The spacing of the three screws will be
accurate enough if the wheel arms be taken as a guide. If all this has
been correctly done, the wheels will go to their places quite true,
both in the round and the flat, and may be taken off for polishing, and
replaced true with certainty, any number of times.
The polishing of the pivots should be as fine as possible; all should
be well burnished, to harden them and make them as smooth as possible
if it is a common job; if a fine one with hardened arbors the pivots
may be ground and polished as in watch work; if the workman has a pivot
polisher and some thin square edged laps this is a short job and should
be done before cutting off the centers and rounding the ends of the
pivots. During all this work the wheels, as a matter of course, will be
removed from the pinions, and may now be again temporarily screwed on,
the polishing of them being deferred till the last, as otherwise they
would be liable to be scratched.
LANTERN PINIONS.—The lantern pinion is little understood outside of
clock factories and hence it is generally underrated, especially by
watchmakers and those working generally in the finer branches of
mechanics. It will never be displaced in clock work, however, on
account of the following specific advantages:
1. It offers the greatest possible freedom from
stoppage owing to dirt getting into the pinions, as
if a piece large enough to jam and stop a clock with
cut pinions, gets into the lantern pinion, it will
either fall through at once or be pushed through
between the rounds of the pinion by the tooth of
the wheel and hence will not interfere with its
operation. It is therefore excellently adapted to run
under adverse circumstances, such as the majority of
common clocks are subjected to.
2. Without giving the reasons it is demonstrable
that as smooth a motion may be got by a lantern
pinion as by a solid radial pinion of twice the
number, and that the force required to overcome the
friction of the lantern is therefore much less than
with the other. It follows that such pinions can be
used with advantage in the construction of all cheap
and roughly constructed clocks which are daily turned
out in thousands to sell at a low price.
3. We have before pointed out the enormous
advantages of small savings per movement in clock
factories which are turning out an annual product of
millions of clocks, and without going into details,
it is sufficient to refer to the fact that where
eight or ten millions of clocks are to be made
annually the difference in the cost of keeping up the
drills and other tools for lantern pinions over the
cost of similar work on the cutters for solid pinions
is sufficient to have a marked influence upon the
cost of the goods. Then the rapidity with which they
can be made and the consequent smallness of the plant
as compared with that which must be provided for
turning out an equal number of cut pinions is also a
factor. There are other features, but the above will
be sufficient to show that it is unlikely that the
lantern pinion will ever be displaced in the majority
of common clocks. From seventy-five to ninety per
cent of the clocks now made have lantern pinions.
The main difference between lantern and cut pinions mechanically is
that as there is no radial flank for the curve of the wheel tooth to
press against in the lantern pinion the driving is all done on or after
the line of centers, except in the smaller numbers, and hence the
engaging or butting friction is entirely eliminated when the pinion
is driven, as is always the case in clock work. Where the pinion is
the driver, however, this condition is reversed and the driving is all
before the line of centers, so that it makes a very bad driver and
this is the reason why it is never used as a driving pinion. This, of
course, bars it from use in a large class of machinery.
The actual making of lantern pinions will be found to offer no
difficulties to those who possess a lathe with dividing arrangements,
a slide rest, and a drill holder or pivot polisher to be fixed on it.
The pitch circle, being through the centers of the pins, can be got
with great accuracy by setting the drill point first to the center of
the lathe, reading the division on the graduated head of the slide
rest screw, and moving the drill point outwards to the exact amount
of the semi-diameter of the pitch circle. This presupposes the slide
rest screw being cut to a definite standard, as the inch or the meter,
and all measurements of wheels and pinions being worked out to the same
standard, the choice of the standard being immaterial. If the slide
rest screw is not standardized the pitch circle may be traced with a
graver and the drill set to center on the line so traced.
The heads of the pinions may be made either of two separate discs, each
drilled separately, and carefully fitted on the arbor so that the pins
may be exactly parallel with the arbor; or, of one solid piece bored
through the center, turned down deep enough in the middle, and the
drill sent right through the pin holes for both sides at one operation.
The former way will be necessary when the number of pins is small,
but the latter is better when the numbers are large enough to allow
of considerable body in the center. In either case it is advisable to
drill only part way through one shroud and to close the holes in the
other with a thin brass washer pressed on the arbor and turned up to
look like part of the shroud after the pins are fitted in the holes.
This makes a much neater way of closing the holes than riveting and
takes but a moment where only one or two pinions are being made.
There is no essential proportion for the thickness of the pins or
rounds. In mathematical investigations these are always taken at
first as mere points of no thickness at all; then the diameters are
increased to workable proportions, and the width of the wheel tooth
correspondingly reduced until there is a freedom or a little shake. If
much power has to be transmitted, the pins, or “staves,” as they are
called in large work, have to be strong enough to stand the strain,
but, as the strain in clockwork is very small, the pins need not be
nearly as thick as the breadth of a wheel tooth. In modern factory
practice the custom is to have the diameter of the rounds equal to the
thickness of the leaf of a cut pinion of similar size, the measurement
being taken at the pitch circle of the cut pinion. As we have already
given the proportions observed in good practice on cut pinions they
need not be repeated here. Another practice is to have wheel teeth and
spaces equal; when this is done the spacing of all pinions above six
leaf is to have the rounds occupy three parts and the space five parts.
In some old church clocks, lantern pinions were much used, in many
cases with the pins pivoted and working freely in the ends, or, as they
called them, “shrouds,” but this was a mistake, and they are never
made so now. A simple way for clock repair work is to get some of the
tempered steel drill rod of exactly the thickness desired, hold one end
by a split chuck in the lathe, let the other end run free, and polish
with a bit of fine emery paper clipped round it with the fingers,
when the wire will be ready for driving through the pinion heads, the
holes being made small enough to provide for the rounds being firmly
held. The drill may be made of the same wire. The shrouds may be made
either of brass or steel; the latter need not be hardened, and, when
the rounds are all in place and cut off, the ends may be polished as
desired. In the case of a center wheel, where the pinion is close up to
the wheel, and space cannot be spared, the collet on which the wheel is
mounted may form one end of the pinion head.
[Illustration: Fig. 73. Lantern pinion showing pitch circle.]
[Illustration: Fig. 74. Generating epicycloid curve for lantern pinion
above; compare with curve for cut pinion of same size pitch circle,
page 206.]
THE WHEEL TEETH.—The same principles of calculation belong to these
and solid-cut pinions, the only difference being that the round pins
require wheel teeth of a different shape from those suited to pinion
leaves with radial sides. Both are derived from epicycloidal curves;
the curve used for lantern pinions is derived from a circle of the
_same size_ as the pitch circle of the pinion, while the curve for
wheel teeth to drive radial-sided leaves is derived from a circle of
_half_ that diameter, so that the wheel teeth in the former are more
pointed than in the latter. There also is a farther difference; as was
explained in detail when treating of cut pinions, the curve of the
wheel tooth presses upon the radial flank of the leaf inside its pitch
circle. Now there is no radial flank in the lantern and the curve is
generated from a circle of twice the diameter, so that it is twice as
long—long enough to interfere—so it is cut off (rounded) just beyond
the useful portion of the working curve of the wheel tooth.
Pillars and arbors are simple parts, yet much costly machinery is used
in making them. The wire from which they are made is brought to the
factories in large coils, and is straightened and cut into lengths by
machines. The principle on which wire is straightened in a machine is
exactly the same as a slightly curved piece of wire is made straight in
the lathe by holding the side of a turning tool between the revolving
wire and the lathe rest, which is an operation most of our readers must
have practiced. The rapid revolution of the wire against the turning
tool causes its highest side to yield, till finally it presses on the
turning tool equally all round, and is consequently straight. However,
in straightening wire by machines the wire is not made to revolve, but
remains stationary while the straightening apparatus revolves around
it. Wire-straightening machines are usually made in the form of a
hollow cylinder, having arms projecting from the inside towards the
center. The cylinder is open at both ends, and the arms are adjustable
to suit the different thicknesses of wire. The wire is passed through
the ends of the cylinder, and comes in contact with the arms inside. A
rapid rotary motion is then given to the cylinder, which straightens
the wire in the most perfect manner, as it is drawn through, without
leaving any marks on it when the machine is properly adjusted. The long
spiral lines that are sometimes seen on the wire work of clocks is
caused by this want of adjustment; and they are produced in the same
way as broad circular marks would be made in soft iron wire if the side
of the turning tool was held too hard against it when straightening it
in the lathe.
[Illustration: Fig. 75. A Slide Gauge Lathe.]
After the wire has been straightened it is cut off into the required
lengths, and this operation is worthy of notice. If the thick sizes of
wire that are used were to be cut by the aid of a file or a chisel, the
ends would not be square, and some time and material would be lost in
the operation of squaring them; and as economy of material as well as
economy of labor is a feature in American clock manufacture, wire of
all sizes is sheared or broken off into lengths, by being fed through
round holes in the shears, which act the same as when a steady pin is
broken when a cock or bridge gets a sudden blow on the side, or in
the same manner as patent cutting plyers work. The wire is not bent
in the operation, and both ends of it are smooth and flat. The wire
for the pillars is then taken to a machine to have the points made and
the shoulders formed for the frames to rest against. This machine is
constructed like a machinist’s bench lathe, with two headstocks. There
is a live spindle running in both heads. In the ends of these spindles,
that point towards the center of the lathe, cutters are fastened,
and the one is shaped so that it will form the end and shoulder of
the pillar that is to be riveted, while the other is shaped so as to
form the shoulder and point that is to be pinned. Between these two
revolving cutters there is an arrangement, worked by a screw in the
end of a handle, for holding the wire from which the pillar is to be
made, in a firm and suitable position. The cutters are then made to
act simultaneously on the ends of the wire by a lever acting on the
spindles, and the points and shoulders are in this way formed in a very
rapid manner, all of the same length and diameter. These machines are
in some points automatic. The pieces of wire are arranged in quantities
in a long narrow feed box that inclines towards the lathe, and the
mechanism for holding the wire is so arranged that when its hold is
loosened on the newly made pillar, the pillar drops out into a box
beneath, and a fresh piece of wire drops in and occupies its place.
In many of the factories, some clocks are manufactured having screws
in place of pins to keep the frames together, and the pillars of
these clocks are made in a different manner than that we have just
described. The wire that is used is not cut into short lengths, but
a turret lathe with a hollow spindle is used, through which the wire
passes, and is held by a chuck, when a little more than just the length
that is necessary to make the pillar projects through the chuck. The
revolving turret head of the lathe has cutting tools projecting from it
at several points. One tool is adapted to bore the hole for the screw,
and when it is bored the next tool taps the hole to receive the screw,
while another forms the point and shoulder; and after that end of the
pillar is completed another tool attached to the slide of the lathe
forms the other shoulder, prepares that end for riveting, and cuts it
off at the same time. One thousand of these pillars are in this manner
made in a day on each machine. The screws that screw into them are made
on automatic screw machines. The latest improvements in this direction
being to first turn the blanks and then roll the threads on thread
rolling machines.
[Illustration: Fig. 76. Slide Gauge Tools and Rack.]
The pinion arbors, after they have been cut to length, are centered
on one end by a milling machine having a conical cutter made for the
purpose. The collets for the pinion heads, and the one to fasten the
wheel by, are punched out of sheet brass, and a hole is drilled in
their centers a little smaller than the wire; and to drive them on,
in most instances, is all that is necessary to hold them. At one time
it was the practice to drive these collets by hand. One was placed
on the point of the arbor, and the point was then placed over a
piece of steel, with a series of holes in it of such depths that the
collets would be in their proper position on the arbor when the point
was driven to the bottom of the hole, but this method has now been
superseded by automatic machinery, which will be described later. It
is impossible to give an intelligible description of these machines
without drawings. All we can say at present is that they perform their
work in a very rapid and effective manner, and are in use by all the
larger clock factories.
The barrels of weight clocks are mostly made from brass castings,
and slight projections are raised on the surface of their arbors by
swedging, so as to prevent the arbors from getting loose in the barrels
after repeated winding of the clock. This swedging and all the other
operations in making arbors used to be done on separate machines; but
the largest companies now use a powerful and comprehensive machine that
works automatically, and straightens any size of wire necessary to be
used in a clock, cuts it to the length, centers it, and also swedges
the projections on the barrel arbors, or any of the other arbors that
may be necessary. A roll of wire is placed on a reel at one end of
the machine, first passing through a straightening apparatus, and
afterwards to that portion of the machine where the cutting, swedging
and centering are executed, and the finished arbors drop into a box
placed ready to receive them. The saving effected by the use of this
machine is very great, and in some instances amounts to a thousand per
cent over the method of straightening, cutting, swedging and centering
on different machines, at different operations.
Boring the holes in the arbors of the locking work, to receive the
smaller wires, and the pin holes in the points of the pillars, is done
by small twist-drills, run by small vertical drill presses. The work
is held in adjustable frames under the drill, and when more than one
hole has to be bored this frame is moved backward or forward between
horizontal slides to the desired distance, which is regulated by an
adjustable stop, so that every hole in each piece is exactly in the
same position. In arbors where holes have to be bored at right angles
to each other, the arbor is turned round to the desired position by
means of an index. The holes in the locking work arbors are bored just
the size to fit the wire that is to go into them, and these small wires
are easily and rapidly fastened in place by holding them in a clamp
made for the purpose, and riveting them either with a hammer or with a
hammer and punch.
[Illustration: Fig. 77. Automatic Pinion Making Machine of the
Davenport Machine Company.]
THE SLIDE GAUGE LATHE.—The system of turning with the slide gauge
lathe, formerly adopted for lantern pinions in the clock factories,
would seem to the watchmaker of a peculiarly novel nature. The turning
tools are not held in the hand, in the manner generally practiced,
neither are they held in the ordinary slide rest, but are used by a
combination of both methods, which secures the steadiness of the one
plan and the rapidity of the other. Adjustable knees are fastened to
the head and tail stocks of the lathe, Figs. 75 and 76, which answer
the purpose of a rest; both the perpendicular and horizontal parts
of these knees being fastened perfectly parallel with the centers of
the lathe. A straight, round piece of iron, of equal thickness, and
having a few inches in the center of a square shape, mortised for the
reception of cutters, is laid on these knees, and answers the purpose
of a handle to hold the cutting tools. Two handles will thus hold
eight tools, one set for brass and one for steel. On every side of the
square part of this iron bar, or what we will now call the turning tool
handle, a number of cutting tools are fastened by set screws, and the
method of using them is as follows: The operator holds the tool handle
with both hands on to the knees that are fastened to the head and tail
stocks of the lathe, with the turning tool that is desired to be used
pointing towards the center, and it is allowed to come in contact with
the work running in the lathe in the usual manner practiced in turning.
Fig. 76 is from a photo furnished by Mr. H. E. Smith of the Smith
Novelty Co., Hopewell, N. J., and shows the tools in the rack, which
is wound with leather so that the tools may be rapidly thrown in place
without injury.
[Illustration]
[Illustration: Fig. 78. Showing Successive Steps in Turning on
Automatic Pinion Making Machine.
Stock advanced.
First collet driven.
Second collet driven.
Third collet driven.
Shoulder turned.
First sides faced.
Second sides faced.
Pivots turned.
Pivots burnished.
Cut off.]
If a plain, straight piece of work is to be turned, the tool is
adjusted in the handle so that the work will be of the proper
diameter when the round parts of the handle come in contact with the
perpendicular part of the knees or rest; and while the handle is thus
held and moved gently along in the corners of the knees, with the tool
sliding on the T-rest, the work is easily turned perfectly parallel,
smooth and true. Sometimes a roughing cut is taken by holding the bar
loosely and then a finishing cut is made with the same tool by holding
it firmly in place. In turning a pinion arbor, for instance, the wire
having been previously straightened and cut to length and centered, and
the brass collets to make the pinion and to fasten the wheel having
been driven on, one end is held in the lathe by a spring chuck fastened
to the spindle of the lathe, while the other end works in a center in
the other head. One turning tool is shaped and adjusted in the handle
for the purpose of turning the brass collets for the pinion to the
proper diameter, another turns the sides of the brass work, while
others are adapted for the arbors, pivots, and so on, pins being placed
in holes in the T-rest to act as stops for the tools. After the brass
work has been turned, the positions of the shoulders of the pivots are
marked with a steel gauge, and by simply turning round the handle of
the turning tool till the proper shaped point presents itself, each
operation is accomplished rapidly, and the cutting is so smooth that
even for the pivots all that is necessary to finish them is simply to
bring them in contact with a small burnisher. The article is not taken
from the lathe during the whole process of turning, and when completed
the centers are broken off, having been previously marked pretty deep
at the proper place with a cutting point. Five hundred to 1,200 arbors
per day, per man, is the usual output. All the pinions, arbors, and
barrels—in fact every part of an American clock movement that requires
turning—were formerly done in this manner, at long rows of lathes
in rooms, and by workmen set apart for the purpose. But perhaps it
may be well to mention that in the machine shops of these factories,
where they make the tools, the ordinary methods of turning with the
common hand tool, and by the aid of ordinary and special slide rests,
are practiced the same as it is among other machinists. In the large
factories automatic turret machines are now coming into use and these
are shown in Figs. 77, 78 and 79.
[Illustration: Fig. 79. Automatic Pinion Drill of the Davenport Machine
Company.]
The lantern pinions of an American clock have long been a mystery to
those unacquainted with the method of their manufacture, and the usual
accuracy in the position of the small wires or “rounds,” combined
with great cheapness, has often been a subject of remark. The holes
for the wires in these pinions are drilled in a machine constructed
as follows: An iron bed with two heads on it, Fig. 80, one of which
is so constructed that by pulling a lever the spindle has a motion
lengthwise as well as the usual circular motion, and on the point of
this spindle, which is driven at 22,000 revolutions, the drill is
fastened that is to bore the holes in the pinions; the other head has
an arbor passing through it with an index plate attached, having holes
in the plate, and an index finger attached to a strong spring going
into the holes, the same as in a wheel cutting engine; on this head,
and on the end of it that faces the drill, there is a frame fastened
in which the pinion that is to be bored is placed between centers, and
is carried round with the arbor of the index plate, in the same manner
as a piece of work is carried round in an ordinary lathe by means of
a dog, or carrier; only in the pinion drilling machine the carrier is
so constructed that there is no shake in any way between the pinion
and the index arbor. This head is carried on a slide having a motion
at right angles to the spindle of the other head, by which means the
pitch diameter of the proposed pinion is adjusted. The head is moved
in the slide by an accurately cut screw, to which a micrometer is
attached that enables the workman to make an alteration in the diameter
of a pinion as small as the one-thousandth part of an inch. The drill
that bores the holes is the ordinary flat-pointed drill, and has a
shoulder on its stem that stops the progress of the drill when it has
gone through the first part of the pinion head and nearly through the
other. All operators make their own drills and the limits of error are
for pitch diameter .0005 inch; error of size of drills .0001. The reader
can see that these men must know something of drill making.
[Illustration: Fig. 80. Pinion Drilling Machine.]
The action of the machine is simple. The pinion, after it has been
turned, pivoted and dogged, is placed in its position in the machine,
and by pulling a lever, the drill, which is running at a speed of about
22,000 revolutions a minute, comes in contact with the brass heads of
the pinion and bores the one through and the other nearly through. The
lever is then let go, and a spring pulls the drill back; the index is
turned round a hole, and another hole bored in the pinion, and so on
till all the holes are bored. An ordinary expert workman, with a good
machine, will bore about fourteen hundred of medium-sized pinions in
a day. The wires or “rounds” are cut from drill rod and are put into
the holes by hand by girls who become very expert at it. This is called
“filling.” We have already stated that the holes are only bored partly
through one of the pieces of the brass, and after the wire has been
put in, the holes are riveted over, and in this manner the wires are
fastened so that they cannot come out. Some factories close the holes
by a thin brass washer forced on the arbor, instead of riveting.
Figs. 77, 78 and 79 show the automatic pinion turning machine and its
processes in successive operations. These machines are used by most
of the large clock manufacturers of the United States and some of the
European concerns also. They are entirely automatic, will make 1,500
pinions per day, as an average, and one man can run four machines.
Fig. 79 shows an automatic pinion drilling machine, which takes up the
work where it is left by the machine shown in Fig. 77. This machine
will drill 4,000 to 5,000 pinions per day according to the size hole
and the number of holes. The operator places the pinions in the special
chain shown in the front of the machine, from which the transport arms
carry them to the spindle, where they are drilled and when completed
drop out. One operator can feed three of these machines.
MAKING SOLID PINIONS.—The solid steel pinions are not hardened, but
are made of Bessemer steel, which could only be case hardened—a thing
hardly ever done. The process of making these pinions is as follows:
Rods of Bessemer steel are cut into suitable lengths. The pieces
obtained are pointed or centered on both ends. The stock not needed for
the pinion head is cut away, leaving the arbors slightly tapering, for
the purpose of fastening them by this means in a hole on the cutting
machine. On the end of the arbor of the index plate are two deep cuts
across its center, and at right angles to each other. These cuts are
of the same shape that would be made by a knife edged file. The effect
of these cuts is to produce a taper hole in the end of the arbor, with
four sharp corners. Into this hole the end of the arbor of the pinion
or ratchet that is to be cut is placed, and a spring center presses on
the other end, and the sharp corners in the hole hold the work firm
enough to prevent it from turning round when the teeth are being cut.
The marks that are to be seen on the shoulder of the back pivot of the
arbor that carries the minute hand of a Yankee clock is an illustration
of this method of holding the pinion when the leaves are being cut, and
no injurious effects arise from it. The convenience the plan affords
for fastening work in the engine enables twenty-five hundred of these
pinions to be cut in a day, one at a time. The pinion head is cut
subject to the proper dividing plate by a splitting circular saw, and
by a milling tool (running in oil) for forming the shape of the leaves,
both of which tools are generally carried on the same arbor, both being
shifted into their proper places by an adjusting attachment. Pinion
leaves of the better class are generally shaped by two succeeding
milling cutters, the second one of which does the finishing, obviating
any other smoothing. For very cheap work the arbors receive no further
finish. The shaping of the pivots, done by an automatic lathe, finishes
the job.
Figure 81 shows an automatic pinion cutting machine which has extensive
use in clock factories for cutting pinions up to one-half inch diameter
and also the smaller wheels. For wheels the work is handled in stacks
suited to the traverse of the machine, the work being treated as if the
stacks were long brass pinions.
[Illustration: Fig. 81. Automatic Wheel and Pinion Cutters.]
Wheels are cut in two ways, on automatic wheel cutters as just
described and on engines containing parallel spindles for the cutters,
carried in a yoke which rises and falls, so that it clears the work
while the carriage is returning to the starting point on each trip and
engages it on the outward trip. The cutters are about three inches in
diameter and rapidly driven; the first is a saw, the second a roughing
cutter, and the third a finishing cutter. The carriage is driven by a
rack and pinion operated by a crank in the hands of the workman and
streams of soda water are used on the cutters and work to carry away
the heat, as brass expands rapidly under heat, and if the stack were
cut dry the cut would get deeper as the cutting proceeded, owing to the
expansion of the brass, and hence the finished wheel would not be round
when cold, if many teeth were being cut. The stacks of wheels are about
four inches in length and the slide thus travels about twenty inches
in order to clear the three arbors and engage with the shifter for the
index. The last wheel of the stack has a very large burr formed by the
cutters as they leave the brass and this wheel is removed from the
stack when the arbor is taken out and placed aside to have the burrs
removed by rubbing on emery paper.
[Illustration: Fig. 82. Wheel Cutting Engine.]
This is one of the few instances in which automatic machinery has been
unable to displace hand labor, as the work is done so quickly that
the time of the attendant would be nearly all taken up in placing and
removing the stacks, and so the feeding is done by him as well. About
35,000 wheels per day can be thus cut by one man, with girls to stack
the blanks on the arbors, and an automatic feed would not release the
man from attendance on the machine, so that the majority of clock
wheels are cut to-day as they were forty years ago. Still, some of
the factories are adding an automatic feed to the carriage in the
belief that the increased evenness of feed will give a more accurately
cut wheel, a proposition which the men most vigorously deny. Such a
machine, they say, to be truly automatic, must take its stacks of
wheels from a magazine and discharge the work when done, so that one
attendant could look after a number of machines. This would result in
economy, as well as accuracy, but has not been done owing to the great
variations in sizes of wheels and numbers of teeth required in clock
work.
Figure 82 shows one of these machines, a photograph of which was taken
especially for us by the courtesy of the Seth Thomas Clock Company at
their factory in Thomaston, Conn.
About every ten years some factory decides to try stamping out the
teeth of wheels at the same time they are being blanked; this can, of
course, be done by simply using a more expensive punch and die, and
at first it looks very attractive; but it is soon found that the cost
of keeping up such expensive dies makes the wheels cost more than if
regularly cut and for reasons of economy the return is made to the
older and better looking cut wheels.
After an acid dip to remove the scale on the sheet brass, followed by a
dip in lacquer, to prevent further tarnish, the wheels are riveted on
the pinions in a specially constructed jig which keeps them central
during the riveting and when finished the truth of every wheel and its
pinions and pivots are all tested before they are put into the clocks.
The total waste on all processes in making wheels and pinions is from
two to five per cent, so that it will readily be seen that accuracy is
demanded by the inspectors. European writers have often found fault
with nearly everything else about the Yankee clock, but they all unite
in agreeing that the cutting and centering of wheels, pinions and
pivots (and the depthing) are perfect, while the clocks of Germany,
France, Switzerland and England (particularly France) leave much to be
desired in this respect; and much of the reputation of the Yankee clock
in Europe comes from the fact that it will run under conditions which
would stop those of European make.
We give herewith a table of clock trains as usually manufactured, from
which lost wheels and pinions may be easily identified by counting the
teeth of wheels and pinions which remain in the movement and referring
to the table. It will also assist in getting the lengths of missing
pendulums by counting the trains and referring to the corresponding
length of pendulums. Thus, with 84 teeth in the center wheel, 70 in the
third, 30 in the escape and 7-leaf pinions, the clock is 120 beat and
requires a pendulum 9.78 inches from the bottom of suspension to the
center of the bob.
TO CALCULATE CLOCK TRAINS.—Britten gives the following rule: Divide the
number of pendulum vibrations per hour by twice the number of escape
wheel teeth; the quotient will be the number of turns of escape wheel
per hour. Multiply this quotient by the number of escape pinion teeth,
and divide the product by the number of third wheel. This quotient
will be the number of times the teeth of third wheel pinion must be
contained in center wheel.
Clock Trains and Lengths of Pendulums.
===========+=========+========+==============+==========
| | | Vibrations | Length of
| | Escape | of Pendulum | Pendulum
Wheels | Pinions | Wheel | —Min. | in Inches
-----------+---------+--------+--------------+----------
120 90 75| 10 10 9| Double | *30 | 156.56
| |3 legged| |
120 90 90| 10 9 9 | Do. | *40 | 88.07
128 120| 16 | 30 | 60 | 39.14
112 105| 14 | 30 | 60 | 39.14
96 90| 12 | 30 | 60 | 39.14
80 75| 10 | 30 | 60 | 39.14
64 60| 8 | 30 | 60 | 39.14
68 64| 8 | 30 | 68 | 30.49
70 64| 8 | 30 | 70 | 28.75
72 64| 8 | 30 | 72 | 27.17
75 60| 8 | 32 | 75 | 25.05
72 65| 8 | 32 | 78 | 23.15
75 64| 8 | 32 | 80 | 22.01
84 64| 8 | 30 | 84 | 19.97
86 64| 8 | 30 | 86 | 19.06
88 64| 8 | 30 | 88 | 18.19
84 78| 7 | 20 | 89.1 | 17.72
80 72| 8 | 30 | 90 | 17.39
84 78| 7 | 21 | 93.6 | 16.08
94 64| 8 | 30 | 94 | 15.94
84 78| 8 | 28 | 95.5 | 15.45
108 100| 12 & 10 | 32 | 96 | 15.28
84 84| 9 & 8 | 30 | 98 | 14.66
84 78| 7 | 22 | 98 | 14.66
84 78| 8 | 29 | 98.9 | 14.41
80 80| 8 | 30 | 100 | 14.09
85 72| 8 | 32 | 102 | 13.54
84 78| 8 | 30 | 102.4 | 13.44
84 78| 7 | 23 | 102.5 | 13.4
105 100| 10 | 30 | 105 | 12.78
84 78| 8 | 31 | 105.8 | 12.59
84 78| 7 | 24 | 107 | 12.3
96 72| 8 | 30 | 108 | 12.08
84 78| 8 | 32 | 109.2 | 11.82
88 80| 8 | 30 | 110 | 11.64
84 77| 7 | 25 | 110 | 11.64
84 78| 7 | 25 | 111.4 | 11.35
84 80| 8 | 32 | 112 | 11.22
84 78| 8 | 33 | 112.6 | 11.11
96 76| 8 | 30 | 114 | 10.82
115 100| 10 | 30 | 115 | 10.65
84 78| 7 | 26 | 115.9 | 10.49
96 80| 8 | 30 | 120 | 9.78
84 70| 7 | 30 | 120 | 9.78
84 78| 7 | 27 | 120.3 | 9.73
90 84| 8 | 31 | 122 | 9.46
84 78| 7 | 28 | 124.8 | 9.02
100 80| 8 | 30 | 125 | 9.01
90 84| 8 | 32 | 126 | 8.87
100 96| 10 | 40 | 128 | 8.59
84 78| 7 | 29 | 129.3 | 8.42
100 78| 8 | 32 | 130 | 8.34
84 77| 7 | 30 | 132 | 8.08
84 78| 7 | 30 | 133.7 | 7.9
90 90| 8 | 32 | 135 | 7.73
84 78| 7 | 31 | 138.2 | 7.38
84 80| 8 | 40 | 140 | 7.18
120 71| 8 | 32 | 142 | 6.99
84 78| 7 | 32 | 142.6 | 6.93
100 87| 8 | 32 | 145 | 6.69
84 78| 7 | 33 | 147.1 | 6.5
100 96| 8 | 30 | 150 | 6.26
84 78| 7 | 34 | 151.6 | 6.1
96 95| 8 | 32 | 152 | 6.09
84 77| 7 | 35 | 154 | 5.94
104 96| 8 | 30 | 156 | 5.78
84 78| 7 | 35 | 156 | 5.78
120 96| 9 & 8 | 30 | 160 | 5.5
84 78| 7 | 36 | 160.5 | 5.47
84 78| 7 | 37 | 164.9 | 5.15
132 100| 9 & 8 | 27 | 165 | 5.17
84 78| 7 | 38 | 169.4 | 4.88
128 102| 8 | 25 | 170 | 4.87
84 78| 7 | 39 | 173.8 | 4.65
36 36 35| 6 | 25 | 175 | 4.6
84 77| 7 | 40 | 176 | 4.55
84 78| 7 | 40 | 178.3 | 4.43
45 36 36| 6 | 20 | 180 | 4.35
47 36 36| 6 | 20 | 188 | 3.99
===========+=========+========+==============+==========
* These are good examples of turret clock trains; the great
wheel (120 teeth) makes in both instances a rotation in
three hours. From this wheel the hands are to be driven.
This may be done by means of a pinion of 40 gearing with
the great wheel, or a pair of bevel wheels bearing the
same proportion to each other (three to one) may be used,
the larger one being fixed to the great wheel arbor. The
arrangement would in each case depend upon the number and
position of the dials. The double three-legged gravity
escape wheel moves through 60° at each beat, and therefore
to apply the rule given for calculating clock trains it must
be treated as an escape wheel of three teeth.
Take a pendulum vibrating 5,400 times an hour, escape wheel of 30,
pinions of 8, and third wheel of 72. Then 5,400 ÷ 60 = 90. And
90 × 8 ÷ 72 = 10. That is, the center wheel must have ten times as many
teeth as the third wheel pinion, or ten times 8 = 80.
The center pinion and great wheel need not be considered in connection
with the rest of the train, but only in relation to the fall of the
weight, or turns of mainspring, as the case may be. Divide the fall
of the weight (or twice the fall, if double cord and pulley are used)
by the circumference of the barrel (taken at the center of the cord);
the quotient will be the number of turns the barrel must make. Take
this number as a divisor, and the number of turns made by the center
wheel during the period from winding to winding as the dividend;
the quotient will be the number of times the center pinion must be
contained in the great wheel. Or if the numbers of the great wheel
and center pinion and the fall of the weight are fixed, to find the
circumference of the barrel, divide the number of turns of the center
wheel by the proportion between the center pinion and the great wheel;
take the quotient obtained as a divisor, and the fall of the weight as
a dividend (or twice the fall if the pulley is used), and the quotient
will be the circumference of the barrel. To take an ordinary regulator
or 8-day clock as an example—192 (number of turns of center pinion in
8 days) ÷ 12 (proportion between center pinion and barrel wheel) = 16
(number of turns of barrel). Then if the fall of the cord = 40 inches,
40 × 2 ÷ 16 = 5, which would be circumference of barrel at the center
of the cord.
If the numbers of the wheels are given, the vibrations per hour of the
pendulum may be obtained by dividing the product of the wheel teeth
multiplied together by the product of the pinions multiplied together,
and dividing the quotient by twice the number of escape wheel teeth.
The numbers generally used by clock makers for clocks with less than
half-second pendulum are center wheel 84, gearing with a pinion of 7;
third wheel 78, gearing with a pinion of 7.
The product obtained by multiplying together the center and third wheels
= 84 × 78 = 6,552. The two pinions multiplied together = 7 × 7 = 49.
Then 6,552 ÷ 49 = 133.7. So that for every turn of the center wheel the
escape pinion turns 133.7 times. Or 133.7 ÷ 60 = 2.229, which is the
number of turns in a minute of the escape pinion.
The length of the pendulum, and therefore the number of escape wheel
teeth, in clocks of this class is generally decided with reference to
the room to be had in the clock case, with this restriction, the escape
wheel should not have less than 20 nor more than 40 teeth, or the
performance will not be satisfactory. The length of the pendulum for
all escape wheels within this limit is given in the preceding table.
The length there stated is of course the theoretical length, and the
ready rule adopted by clockmakers is to measure from the center arbor
to the bottom of the inside of the case, in order to ascertain the
greatest length of pendulum which can be used. For instance, if from
the center arbor to the bottom of the case is 10 inches, they would
decide to use a 10-inch pendulum, and cut the escape wheel accordingly
with the number of teeth required as shown in the table. But they would
make the pendulum rod of such a length as just to clear the bottom of
the case when the pendulum was fixed in the clock.
In the clocks just referred to the barrel or first wheel has 96 teeth,
and gears with a pinion of eight.
Month clocks have an intermediate wheel and pinion between the great
and center wheels. This extra wheel and pinion must have a proportion
to each other of 4 to 1 to enable the 8-day clock to go 32 days from
winding to winding. The weight will have to be four times as heavy,
plus the extra friction, or if the same weight is used there must be a
proportionately longer fall.
Six-months clock have two extra wheels and pinions between the great
and center wheels, one pair having a proportion of 4½ to 1 and the
other of 6 to 1. But there is an enormous amount of extra friction
generated in these clocks, and they are not to be recommended.
The pivot holes and all the other holes in the frames, are punched at
one operation after the frames have been blanked and flattened. They
are placed in the press, and a large die having punches in it of the
proper size and in the right position for the holes, comes down on the
frame and makes the holes with great rapidity and accuracy. These holes
are finished afterwards by a broach. In some kinds of clocks, where
some of the pivot holes are very small, the small holes are simply
marked with a sharp point in the die, and afterwards drilled by small
vertical drills. These machines are very convenient for boring a number
of holes rapidly. The drill is rotated with great speed, and a jig or
plate on which the work rests is moved upwards towards the drill by
a movement of the operator’s foot. All the boring, countersinking,
etc., in American clocks, is done through the agency of these drills.
Bending the small wires for the locking work, the pendulum ball, etc.,
is rapidly effected by forming. As no objectionable marks have been
made on the surface of either the thick or smaller wires during any
process of construction, all that is necessary to finish the iron work
is simply to clean it well, which is done in a very effective manner by
placing a quantity of work in a revolving tumbling box, which is simply
a barrel containing a quantity of sawdust.
Milling the winding squares on barrel arbors is an ingenious operation.
The machine for milling squares and similar work is made on the
principle of a wheel cutting engine. The work is held in a frame,
attached to which is a small index plate, like that of a cutting
engine. In the machine two large mills or cutters, with teeth in them
like a file, are running, and the part to be squared is moved in
between the revolving cutters, which operation immediately forms two
sides of the square. The work is then drawn back, and the index turned
round, and in a like manner the other two sides of the square are
formed. The cutting sides of the mills are a little bevelled, so that
they will produce a slight taper on the squares.
Winding keys have shown great improvements. Some manufacturers
originally used cast iron ones, but the squares were never good in
them, and brass ones were adopted. At first the squares were made by
first drilling a hole and driving a square punch in with a hammer;
and to make the squares in eighteen hundred keys by this method was
considered a good day’s work. Restless Yankee ingenuity, however, has
contrived a device by which twenty or twenty-five thousand squares can
be made in a day, while at the same time they are better and straighter
squares than those by the old method; but we are not at liberty to
describe the process at present, but only to state that it is done by
what machinists call drilling a square hole.
Pendulum rods are made from soft iron wire, and the springs on the
ends rolled out by rollers. Two operations are necessary. The first
roughs the spring out on rollers of eccentric shape, and the spring
is afterwards finished on plain smooth rollers. The pendulum balls in
the best clocks are made of lead, on account of its weight, and cast
in an iron mold in the same manner as lead bullets, at the rate of
about eighteen hundred a day. A movable mandrel is placed in the mold
to produce the hole that is in the center of the ball. The balls are
afterwards covered with a shell of brass, polished with a bloodstone
burnisher. The various cocks used in these clocks are all struck up
from sheet brass, and the pins in the wheels in the striking part are
all swedged into their shape from plain wire. The hands are die struck
out of sheet steel, and afterwards polished on emery belts, and blued
in a furnace.
All the little pieces of these clocks are riveted together by hand, and
the different parts of the movement, when complete, are put together by
workmen continually employed in that department. Although the greatest
vigilance is used in constructing the different parts to see that they
are perfect, when they come to be put together they are subjected to
another examination, and after the movements are put in the case the
clocks are put to the test by actual trial before they are packed ready
for the market. As a general rule, all the different operations are
done by workmen employed only at one particular branch; and in the
largest factories from thirty to fifty thousand clocks of all classes
may be seen in the various stages of construction.
Such is a description of the main points in which the manufacture of
American clock movements differs from those manufactured by other
systems. All admit that these clocks perform the duties for which they
are designed in an admirable manner, while they require but little
care to manage, and when out of order but little skill is necessary
to repair them. Of late years there has been a growing demand for
ornamental mantel-piece clocks in metallic cases of superior quality,
and large numbers of these cases of both bronze and gold finish are
being manufactured, which, for beauty of design and fine execution,
in many instances rival those of French production. The shapes of the
ordinary American movements were, however, unsuitable for some patterns
of the highest class of cases, and the full plate, round movements of
the same size as the French, but with improvements in them that in some
respects render them more simple than the French, are now manufactured.
Exactly the same system is employed in the manufacture of the different
parts of these clocks that is practiced in making the ordinary American
movements.