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Question:
"Recently
I bought a sports watch and the salesperson
told me that it was equipped with an anti-shock
device. What is this device and how does it
work?"
Kino
Tanaka, Japan
Answer
by Professor J.C. Nicolet
Today,
it has become nearly unthinkable to sell a sports
watch that is not equipped with some sort of
anti-shock mechanism, or shock absorber as they
are sometimes called. This device is basically
a resilient bearing designed to damp the shocks
brought to bear on the balance-staff pivots.
A
watch is a delicate mechanism composed of many
parts, some of which are extremely fragile.
For example, the tiny pivots of certain wheels
have a diameter of the order of 10 to 12 hundredths
of a millimeter (about the size of a strand
of hair). The regulator of a watch is a relatively
heavy circular wheel whose pivots are among
the most delicate parts of the timepiece. If
the watch falls onto a hard surface and there
is nothing to absorb the shock, the tiny pivots
will break. Violent movements made by certain
athletes or even card players, if they bang
their fists on the table, are enough to break
or bend the pivots of the balance-staff, necessitating
expensive repairs.
In
the 1920s, wristwatches became fairly widespread
and with their use, so did the number of "aggressions"
the watches were subjected to. Even though less
prone to this type of problem, pocket watches
also suffered the same sort if dropped.
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| This
drawing illustrates the principle of an
anti-shock mechanism. The endstone, a,
is subject to the action of a spring,
b. If an axial shock occurs, the
endstone can lift slightly until the shoulder,
c, strikes a fixed part of the
setting. To damp lateral shocks, the jewel
hole is fitted in a setting comprising
an inclined plane, d, which provides
for a slight lateral shift limited by
the collet-arbor or by the roller-arbor,
e, which strikes a fixed part of
the frame. |
A
bit of history
As
early as the 18th century, the first attempts
to protect pocket watches against shocks consisted
of placing them in a series of successively
larger cases, each having a certain amount of
play in relation to the next. This type of protection
was used mostly for watches intended for use
in Turkey and for those worn by the cavalry
and other horsemen (the sportsmen of the era).
The watch was placed within two, three or even
four larger cases with the first case being
rather simple, while the last was often covered
with leather. This system of shock protection
was without a doubt effective but not very practical.
Just to read the hour, one had to spend time
opening up several cases.
A
little before 1800, Abraham-Louis Breguet, often
called the watchmaker of kings and the king
of watchmakers, invented a shock-absorbing device
called a "pare-chute" intended to
protect the pivots of the balance-staff in case
of a fall. He replaced the cylindrical part
of the pivot by a cone which itself would turn
in a ruby cup-bearing mounted in a spring capable
of either axial or lateral displacement. In
case of a shock, the cup-bearing would move,
thus taking the impact of the shock away from
the pivots.
Legend
has it that Breguet, having a strong sense of
publicity, pretended one day to clumsily drop
his pocket watch in front of a group of people
who looked on in horror. Breguet calmly picked
up his faithful timepiece which kept right on
ticking, thus winning himself increased admiration
from his wealthy clientele.
Breguet's
anti-shock mechanism was not within the scope
of just any watchmaker of the day and its high
price effectively excluded it from being used
in most watches. It was only with the introduction
and subsequent general use of the wristwatch
that interest was regenerated in anti-shock
mechanisms.
Incabloc
and company
In
1929, the firm Wyler developed a shock absorber
with fixed bearings which took advantage of
the elasticity of the balance-staff based on
a principle of equal resistance. The staff was
attached to a balance whose arms in the form
of a spiral were themselves elastic.
However,
it was in 1933 that an engineer named Hans Marti
took out a patent on a system of anti-shock
bearings based on a modified version of several
of his competitors. In this device, known under
the commercial name of "Incabloc",
as in other similar systems, the balance jewel
in which the pivot turns, is mounted in a conical
setting, which is itself placed in a solid truncated
cone in the watch's frame. The setting also
supports the endstone. The entire unit is held
in place by a carefully calibrated spring.
When
a lateral or axial shock occurs, the setting
slides into the cone. This movement permits
the pivots to transfer the shock to the frame.
The wheels are then pulled back and recentered
by the spring which also is removable thus permitting
dismantling of the setting and the endstone
without having to remove the balance. This is
a great advantage for cleaning and oiling.
The
mass production of anti-shock devices has brought
down their prices so that they can be added
to watches without an unduly increase in price.
In addition to the ease in assembling and disassembling
the modern shock-absorbing mechanisms, the oil
chamber is protected from dust entry thus ensuring
a longer working life of the watch.
Since
the invention of the anti-shock device, the
balance is no longer the most fragile part of
a watch. However, in the case of very violent
shocks, other components may break but these
in turn are often protected, so that we no longer
worry too much about watches being "shocked
to death". |
