APPLICATION OF THE LAW OF FRICTION AND LUBRICATION IN HOROLOGY.
~45.~ The scope of this work will not permit the discussion of the proper
size, shape and construction of each and every part of all the various
kinds of time-keeping mechanisms which have been produced. However a
number of _representative_ cases of friction and lubrication will be
considered, and the laws applying to the same will be demonstrated.
Practical methods of obtaining the best results will be shown and
mistakes to be avoided will be pointed out.
The knowledge of what we ought not to do is sometimes of vastly greater
importance than it is usually considered to be.
~46. The Proportions of Pivots, Shoulders and Bearings~, where the
bearings are not capped jewels, should be such that the coefficient (33)
of the combined solid and fluid friction will be a minimum, and such
that the lubricant will not be expelled at normal pressure, while the
"fit" (37) must be good.
1. _The diameters of all pivots_ should be of the smallest size
compatible (43,6) with the foregoing condition, and with the stresses
which they are expected to sustain.
2. _The length of bearing surfaces_ is regulated by the pressures which
may occur (43) between them, and by the nature of the materials of which
they may be composed.
3. Given the diameter and the pressure, the length of the bearing
surfaces can be so proportioned as to prevent abrasion and to present
surfaces, between which the film of oil is interposed, of such magnitude
that the lubricant will not be expelled at normal pressure.
[Illustration: Fig. 13.]
4. In Fig. 13 the length of bearing surface of the pivot is equal to its
diameter, but the proportion must be varied according to conditions.
5. The barrel arbor pivots are sometimes necessarily of large diameter,
and the bearing surfaces can be made shorter in proportion, as the
surfaces will then be great enough to give good results as well as to
retain (48) the oil.
6. In the center pinion (49) where the diameter of the the pivots is
made small for reasons explained (43, 6), the length of the bearing
surfaces must be such that abrasion will not occur, and that the oil
will not be expelled.
7. The rest of the train is subject to the same laws. The length of the
bearing surfaces of the pivots remote from the motive force can be made
shorter in proportion.
8. The diameter of the shoulder S, Fig. 13, is reduced to as small a
size as will properly sustain the "end thrust," thus reducing the
friction, both solid and fluid, to a minimum, at the same time reducing
the distance from the center of the arbor (43, 6) at which the friction
acts.
9. The above proportions vary with the nature of the material; where
jewels are employed a shorter bearing surface may be used, if it be
desired to reduce friction, but the pressure on the oil is the same with
jewel as with brass bearings, so that it must not be made so short that
the oil will be expelled.
~47. The Shape of Pivots, Shoulders and Bearings~, where the bearings are
not capped jewels, should be such as to produce as little friction as
possible. They should be hard, symmetrical, and smooth (30).
_The construction should be such that a considerable amount of oil may
be applied without having a tendency to spread._
The advantages of the construction shown at Fig. 13 are:
1. The oil sink _O_ is deep and narrow, rather than wide and flat--thus
causing the oil to be drawn towards the apex of the angle, i. e. towards
the pivot, with greater force (22, 5) than if the oil sink were wide and
shallow, in which case the oil would have a tendency to spread, as too
often occurs.
2. The total length of the pivot is to the length of its bearing surface
as 5 is to 3, thus further reducing the angle, which produces a greater
tendency (22, 5) in the oil to stay in the oil-sink.
3. A circular groove G is cut around the oil sink, which produces a
still greater tendency on the part of the oil to stay in the sink, by
removing metal which would otherwise exert an attraction (19) on the
oil.
4. The beveled portion P is comparatively large--while the shoulder S is
relatively small--thus forming the angle O' of about 20 deg. with the flat
surface of the bearing. This will cause the oil to have a tendency to
flow towards the pivot, for the reason given in considering the
oil-sink.
5. The boss B is made to diminish the liability of the oil to spread, by
a reduction (18-19) of the amount of metal which would otherwise cause
it.
6. The back taper T is made for the same reason. Some watchmakers (?)
seem to think this is added only for ornament, but it is a very
important factor in producing longevity of the oil.
7. The slight chamfer C, in the bearing, serves two purposes; it becomes
a reservoir for oil and removes any burr that might otherwise exist in a
metal bearing, without in any way altering its effectiveness.
8. It will thus be seen that the oil reservoirs O, O' and C are made to
contain, and retain, the maximum amount of oil, and the supply of the
lubricant is thus increased to a maximum length of time.
The application of these principles to each part to which they relate
will be considered.
~48. The Barrel Arbor~, with its bearing, should be so constructed that
the oil will not spread to the contiguous parts. The oil sink, with
circular groove cut around the outside (46-47), both in the barrel and
its cover, should not be neglected.
It is well to apply oil to the bottom and on the cover of the barrel, as
well as on the coils of the spring; and before putting on the cover, a
small amount applied on the arbor nut at the shoulders will assist
greatly in causing the oil to be at once drawn to its proper place.
Care must be exercised while and after cleaning the mainspring, in order
that it may come in contact with the fingers as little as possible, as
the acids contained in perspiration are liable to be transferred to the
spring and so work serious injury by contaminating the oil.
A part frequently neglected is the point of contact of the click spring
with the click. If this part be not oiled rust is likely to form, and
many instances have occurred where rust has found its way all through
the movement from this cause. In fact, this may be said of the point of
contact of all springs, with few exceptions, both in plain and
complicated work.
If the watch has a chain and fusee, these both should be looked after;
the former can be well oiled, and the surplus wiped off so as to leave a
minute quantity in the interstices of the links; while the latter should
have oil on its clicks, as well as on the arbor where it passes through
the wheel. If the ratchet of the maintaining power be of brass it should
not be oiled; while if it is of steel oil should be applied. Its click
should have the pivots of its arbor oiled, while what was said of clicks
in general will apply here.
~49. The Center Pinion Pivots~, with their bearings, should be very
carefully constructed, as this is the vulnerable point of most watches.
With proper precautions (46-47) these parts can be made so as to wear as
long as the rest of the watch.
In a high-priced watch the bearings should be jewels; but in a cheap
watch, where the price will not warrant correct work and careful
fitting, the bearings are preferably of brass or some other metal.
Where the bearings of the center pinions are of brass or nickel, there
is little difficulty experienced in making them perfectly "upright"--a
condition necessary to produce a minimum amount of friction--while, if
the bearings are jewels which are not upright, the friction, and
consequent wear, will be increased. Properly jeweled bearings produce a
maximum durability, as they cause the least friction; while the
coefficient of friction is subject to much less fluctuation on account
of the harder, smoother surface of the jewel, (43, 46, 47 and 61).
Where there is a brass bearing for the lower pivot, in watches having a
solid center arbor on which the cannon pinion revolves in setting, the
length of the bearing may be profitably increased by making a boss on
the outer side of the lower plate, provision for which is then made in
the cannon pinion by a suitable recess. In either case the laws
previously given should be complied with.
A source of mischief in many watches is the manner in which the minute
wheel is made; the construction being such that its teeth touch the
plate so near the bearing of the center arbor that capillary attraction
(19, 22) is produced, which causes all the oil to leave the lower
bearing of the center arbor. This can be avoided by cutting off the
lower parts of the teeth of the minute wheel; or, by turning a groove
in the plate which will be concentric with the minute wheel post, and
which will pass under the teeth of the wheel, but not near enough to the
bearing of the center arbor to injure the latter.
The oil from the stem wind mechanism, also, sometimes flows under the
minute wheel, and from there into the center arbor bearing; and, when
the oil is used up in the former place, it is drawn up again out of the
latter place leaving it dry. A means of preventing this will be
discussed (59) later.
Another and _very_ frequent cause of the lower center pivot cutting,
particularly in new watches, is the neglect to remove the polishing
material from the cannon pinion where the center arbor is solid.
A small portion of oil should be applied to the bearings of the minute
wheel, (where its pinion, or the pivot on which it revolves, is steel),
hour wheel, and cannon pinion where the center arbor is solid, and to
the set hands arbor where the center arbor is hollow. The safety pinion
should always be oiled, as it may not otherwise be of much service.
~50. The Third Pinion Pivots~ are sometimes the source of mischief. When
the center wheel is placed above or below the barrel, the upper or lower
pivot of the third pinion receives such great stress that the oil is
forced out in many cases. By increasing the length of the pivot this
could be obviated. The minute wheel is sometimes so close to the lower
bearing of this pinion as to absorb the oil. This can be remedied by
cutting a recess in the lower side of the minute wheel. Where it is
possible to do so the wheels should be so placed on their pinions and
arbors, and at such a distance from the bearing surfaces of the latter,
that the stress on each pivot--the combined result of the weight of the
wheel and the forces acting on it--will be equal.
~51. The Fourth Pinion Pivots~ should follow the same general laws as that
given for the rest of the train; but it should be borne in mind that
fluid friction acts as a retarding force much more perceptibly in the
lighter parts of the train; consequently if no second-hand is to be
carried, very small bearing surfaces should be the rule in this case.
~52. The 'Scape Pinion Pivots~ as well as the shoulders should not be too
large, while there should be sufficient back taper to insure the oil
remaining at the pivots. A very small quantity of oil should be applied,
as, when too much is used, it is liable to work up into the pinion where
the latter is short, as in very thin watches, thus producing, when very
fine dust is added, a mixture that acts much like oil stone power and
oil, which cuts away the leaves of the pinion.
~53. The Lever Arbor Pivots~ should also be small, with small shoulders so
as to reduce fluid friction to a minimum.
It may be well to add that in all uncapped bearings of pivots in the
train, whether they be of jewels or of brass, a slight convex shape can
profitably be given to the surface where the shoulder of the arbor, or
pinion, touches the bearing, thereby reducing not only the surface of
contact at the shoulder, and consequently diminishing the cause of
friction (41), but by reducing the distance from the center, at which
the friction acts, the retarding effect of the friction is much less
(46), thus obtaining a greater effort (25).
~54. The Balance Arbor Pivots and Bearings~, as well as those of the lever
and scape wheel where their pivots run in capped jewels, deserve
_particular_ attention. Fig. 14 shows hole and cap jewels in settings,
but what applies to them is equally applicable to all capped jewels,
with few exceptions.
[Illustration: Fig. 14.]
In Fig. 14 all the laws of capillary action are applied. It has been
shown (22,8) that, when two watch glasses are fixed rigidly relatively
with their convex sides adjacent, if a drop of oil be placed near their
centers it can be shaken from its position only with great difficulty.
The jewels, in this instance, present much the same form, though only a
minute quantity of oil, instead of a drop, is involved; but the same
influences are at work in both cases.
This reservoir, if properly made, will contain enough oil to last a long
time; as, when the oil in the center is used up, that which is _nearer_
the settings will be drawn to the pivot. The writer has said "nearer"
the settings; but _it is very important that the oil should never touch
the setting_ (58).
Both settings are cut away at _aa'_, in order that as little attractive
influence (22) as possible may be exerted on the oil by the metal in the
settings.
Where the adjacent surfaces of the hole and cap jewel are flat and
parallel the oil will usually have a tendency to be drawn to the
setting--the evil effect of which will be shown (58) later--especially
if the hole and cap jewel are at any appreciable distance from each
other; while if they are _too_ close together, the reservoir will not be
sufficiently large.
The conical pivot shown is the usual form in the finer grades of
American watches; and as this form of pivot combines strength with a
minimum tendency to attract the oil from the jewel hole, it is to be
highly recommended. The back-taper T should never be neglected for
reasons previously (47, 6) given. The proportions that should exist
between the diameter of the pivot and the length of its bearing surface,
as well as the shape of the end of the pivot, cannot be discussed here,
as the scope of this work will not permit; but it should be borne in
mind that the smaller the pivots, consistent with strength, the less the
fluid friction will be. The sides of the pivots should be straight and
parallel for a minute distance from their bearing surfaces; while the
form of the rest of the pivot should be a gradually increasing curve,
terminating at the point where the back-taper begins.
The proper proportion of the diameter of the pivot to the diameter of
the jewel hole varies according to conditions; but it has been
previously (37) shown in a general way what this should be.
~55. The Escapements~ should be constructed in such a way that a maximum
durability of oil may be secured. The acting surfaces of the teeth of
the scape wheels should be made as small as possible consistent with
durability (43, 8); while enough metal should be left _near_ the acting
surfaces to be sufficient to retain the oil and prevent its attraction
to the web of the wheel. The teeth of chronometer scape wheels should
not be oiled, as it is liable to seriously alter the rate. When the oil
becomes viscous by oxidation or by cold it would produce too much
variation of fluid friction and so diminish the effort (25) of the
mechanism. Some watchmakers oil the fork of the lever in anchor
escapements _very_ slightly, by applying oil and then using pith to
remove any surplus, while others never oil the fork. The writer has
frequently observed ferric oxide or "rust" on the roller, fork, and on
the plate or potance; but whether this was the result of not oiling or
of oil having been applied which afterward become gummed, or evaporated,
it would be interesting to know.
~56. The Curb Pins~ sometimes produce the ferric oxide mentioned by their
action on the hairspring. This has been remedied by the same method as
used in the fork just referred to, and if a _very minute_ quantity of
oil can be applied--such a minute quantity that if the whole spring were
equally covered by a coating of oil equally _thin_, such film being _so_
thin that it would have _no_ tendency to cause the coils to adhere, or
to cause small particles of matter to adhere--then it may be that this
method deserves notice.
By making a solution of benzine and oil (100 drops of the former with 1
to 10 drops of the latter) and by immersing the hairspring in this
solution and on withdrawing it dry it quickly between soft, fine linen,
it will be found that the coils of the hairspring do not adhere to each
other. The effect that this would produce on the whole spring by way of
preventing rust in damp, warm climates, will be stated (78) later.
~57. The Application Of Oil~ must be attended with great care. The
shoulders of the barrel and center arbors may be profitably oiled before
putting them in their places, applying an additional small amount
afterward. The rest of the pivots should be oiled after the movement is
set up--except in the case of capped jewels--as if oil is applied to
each pivot as the wheel is put in position it would be difficult to keep
the oil in good condition and at its proper place if it should be
necessary to take the movement apart again for any purpose.
The oil is more evenly distributed on the teeth of scape wheels, where
such require lubrication, if a small quantity of oil be applied to each
tooth, or every second or third tooth. A small amount added to the
surfaces on which the teeth act will in most cases be beneficial. If it
be necessary to take the movement partially apart for any purpose, after
it has been oiled, care should be taken not to give the train a too
rapid motion, as the centrifugal force (23) resulting from the rapid
circular motion of the wheels will be liable to cause the oil to leave
the jewel holes and spread upon the surfaces of the jewels, and also
cause the oil to fly off the teeth of the scape wheel to its determent
and that of other parts which are better without oil.
~58. The Method of Oiling Capped Jewels~ has been given by Saunier, as
follows:[11] "When a drop of oil is introduced into the oil cup of the
balance pivot-hole, insert a very fine pegwood point, so as to cause the
descent of the oil. When this precaution is not taken, it frequently
happens that in inserting the balance pivot its conical shoulder draws
away some of the oil, and there is a deficiency both in the hole and on
the endstone." In both the English and American editions, this erroneous
method is repeated.
By this means, only an insufficient quantity of oil can be caused to
flow into the reservoir, as the pressure of the air inside will prevent
the oil flowing in; as, in the case of a glass tube with the upper end
sealed up, it has been shown (22, 2) that the water refused to be drawn
up the tube, even with the added pressure caused by the lower end of the
tube being below the water line. Again, the point of pegwood is liable
to have minute fibres of wood adhering to it, which will be incorporated
with the oil; and its liability to break off, and remain in the jewel
hole, is another reason why pegwood should never be used. The author
advances a method, which is not open to these objections, as follows:
When about to place the cap jewel in position--after the hole jewel is
in place if it be in a setting--a small quantity of oil is placed ON THE
CAP JEWEL, as shown at O, Fig. 14, _being very careful to allow no oil
to spread upon the cap jewel setting_. This setting is then carefully
placed in position; when the oil, if the operation has been skillfully
performed, is seen to be collected in the reservoir _R_ and _in_ the
jewel hole. The appearance which it will assume is shown in Fig. 14. The
advantages which this method possesses are: the reservoir can by this
means be made to contain the maximum quantity of oil; and the oil cup or
sink _S_ is left with its surface dry, thereby exposing less oil to the
influences of the air; and, at the same time the tendency of the oil to
flow towards the shoulder of the pivot is decreased.
Skill is necessary in order to judge of and place the requisite amount
of oil on the cap jewel before putting it in position; as, if too much
is used it is worse than if too little is employed, because the oil
would then flow on to the setting, and from there _between_ the settings
at _b_, when it will rapidly be all drawn _from the bearing_, leaving it
dry, while the _settings_ are copiously supplied. The approximate
relative position which the oil should occupy is shown at _d_, Fig. 14,
in section; and this can be seen by looking through the jewels with a
double eye-glass, when a true circle, concentric with the jewel hole,
will be seen to have formed. This circle represents the limit of the
distance which the oil has flowed from the jewel hole. When too much oil
has been applied, this limit is not a circle, but represents a U.
In the example given, the upper surface of the cap jewel is made flat,
while the lower surface is made convex with a flat space in the center;
as a better view of the end of the pivot and the condition of the oil
can be thereby obtained.
_In no case should the contiguous surfaces of the hole and cap jewel be
both made flat_; as, when their planes are vertical, the oil will be
drawn downwards by gravitation (18), there being no counteracting force
(22) to keep the oil in place. The author has remedied this defect, in
many instances, by cutting a groove around the jewel, leaving only
enough metal near the jewel to hold it, and enough near the edge of the
setting to rest solidly against the other setting.
In some watches, particularly those of Swiss make, the jewel
bezels--both cap and hole--are brought well up around the jewel, while
_a groove is cut around the jewel bezel_. In this instance the oil may
be made to cover the whole inside surface of both jewels, as the groove
will prevent the oil from flowing away to parts where it is not
required.
The reprehensible practice of replacing a broken cap jewel by cutting
away the bezel and placing the new jewel in loosely, cannot be too
severely condemned. The new cheap foreign-made watches contain this
objectionable feature in many instances.
Where the jewels are in settings, sharp instruments, as tweezers, etc.,
should never be used to push the settings in place; as the projections
produced in this manner would not only injure the appearance of the
settings, but would prevent their close contact. Thoroughly _clean_,
well-finished jewel pushers are indispensable; as even pegwood is liable
to leave fibres at least.
The shape of the oiler is a matter of some importance; as with a
poorly-made oiler it is next to impossible to do work satisfactorily.
The tip is preferably of gold, tapering towards the end to about the
size of a second's hand pivot of an eighteen size American movement; but
at the end it should be about three times as wide and flat. A nickel
fastened to the end of a lead-pencil will give the idea approximately.
This large end will cause the oil to remain where it may be readily
applied to the bearing surface, instead of flowing back on the oiler
towards the handle, as it would (22, 7) if the point were tapering.
~59. The Stem Winding Mechanism~ should be thoroughly well made, always
keeping in view that the laws of capillary attraction must be complied
with.
Wherever an angle can be formed, with its apex pointing towards the
place where the oil is required to remain, it should be done.
A very good lubricant for stem wind parts is found in stearine, from
which the animal oils are expressed at cold temperatures, as it is very
thickly fluid at ordinary temperatures; while an _excellent_ lubricant
for this purpose is paraffine--not the wax nor the oil, but that white,
soft substance from which both are obtained (13 & 73). Stearine and
paraffine both possess great viscosity; and, though the fluid friction
is increased by their use, the solid friction is diminished. Then, too,
_the tendency to spread is very much less_.
~60. The Pendant~ is frequently a cause of trouble to the watchmaker. It
is very important that the winding stem be lubricated with a substance
that will not spread at ordinary temperatures. The lubricant should be
applied at all places where steel rubs on steel or other metal. The
winding stem and case spring, and the sleeve if present should have as
much as can be safely applied; as they are so much exposed that rust
often forms, which finds its way down through the movement, frequently
resulting in serious damage to the delicate parts. The bearings of
collet on stem and the pendant screw should also be lubricated.
Attention to these details will also prevent "that squeaking sound"
which, sometimes occurring shortly after a watch has been repaired,
causes the owner to believe that the work was not done properly.
The lubricants just mentioned (59) serve admirably for this purpose.
~61. The Cause of the Cutting of Pivots~, in addition to the effect of
friction (32, 1) and other causes which have been mentioned (49), may be
that minute currents of static electricity are induced between the
surfaces of the pivot and bearing, the oil acting as the electrolyte.
If this be the case, the cause of pivots turning black would appear to
be explained--the molecules of iron becoming electrically disassociated
from the molecules of carbon, the latter being by their nature black,
and being now on the surface in sufficient quantities to make themselves
evident, give the surface the black color. Such is the first stage of
"cutting."
The molecules of iron, becoming incorporated in the now thick and
viscous oil or imbedding themselves in the bearing, act as an abrasive;
the black surface is removed, making the pivot again bright, but
"ringed." The molecules of iron, uniting with the molecules of oxygen
which exist in the oil in its oxidized state, forms ferric oxide.
Ferric oxide is known as colcothar, English-Roth, rouge, crocus, etc.
The above theory is advanced by the author for what it may be worth, as
it seems to explain this curious phenomenon.
FOOTNOTES:
[11] Saunier. Watchmakers' Handbook.