MINUTE AND HOUR ACCUMULATORS border=2 vspace=15 align=”right”>

The vertical clutch design offers another benefit difficult to obtain with a conventional switched intermediate wheel. As illustrated left, the upper center wheel pinion carries both the heart cam
(1) and a plate with finger
(2). The single finger trips both minute and hour accumulators as the center pinion rotates.

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The illustration left shows the finger
(1) about to trip a tooth on the minute accumulator intermediate wheel. The hour intermediate wheel is on the other side. Because the hour intermediate wheel is tripped once each minute, there are two intermediate reduction wheels between the hour intermediate wheel and the hour wheel itself.

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As shown left, both the hour accumulator
(1) and minute accumulator
(2) are detented by simple steel jumper springs. The jumper springs assure that the hour and minute accumulators indicate whole increments and serve as brakes for these wheels.

RESET FUNCTION

Unlike
many
designs
which
use
separate
hammers
for
reset
of
each
of
the
three
registers,
the
clever
Piguet
design
uses
a
single
hammer.
This
simplifies
construction
and
assures
uniform
reset
of
all
registers.
As
shown right
, the
case
pusher
(1)
operates
on
the
reset
lever
(2),
which
operates
the
three-head
hammer
(3).

The hammers operate against the logarithmically curved heart cams, forcing the cam to rotate until the hammer lies in the “top” concavity of the heart (opposite the apex). This is the zero position for all registers. The center wheel and hour accumulator hammers are indicated at the arrows, right.

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AUTOMATIC WINDING

The automatic winding mechanism is a modular unit attached to either the “simple” or rattrapante calibers with three screws. The mechanism is cleverly designed so that there are only two small differences between the units used on the two calibers. The rattrapante
winding unit uses a longer
pinion on the final transfer
wheel (1) and one of the three mounting screws is longer. The ball bearing carrying the central rotor is indicated at
(2).

The elegantly simple mechanism provides winding with the central rotor turning clockwise (as seen from the movement side). This is accomplished with a single click
(arrow). On an automatic winder, the watch must rotate clockwise (as seen from the dial side). The ball bearing carrying the rotor is replaceable by simply replacing the cover of the unit.

RATTRAPANTE
FUNCTION

Like
the
automatic
winding
unit,
the
rattrapante
unit
is a
discrete
module.
On
the
caliber
1186,
it is
literally
sandwiched
between
the
automatic
winding
unit
and
the
movement.
The
rattrapante
unit,
however,
requires
several
changes
to
the
basic
caliber,
a
taller
case
band
and
bezel,
and
the
addition
of a
third
pusher
at 10
o’clock.
Shown
at
right
are
(1)
the
cover;
(2)
the rattrapante
column
wheel;
(3)
the
return
lever
lifting
wheel;
(4)
the
split-seconds
wheel
itself;
and
(5)
the
switching
arm
for
the
return
lever
lifting
wheel.

Utilizing
a
relatively
simple
mechanism,
the
rattrapante
function
is
comprised
of an
additional
center
seconds
hand
that
can
be
stopped
and
started
independently
of
the
main
center
seconds
hand.
The
“zero”
position
of
the
rattrapante
hand
is
alignment
with
the
main
hand,
regardless
of
where
the
main
hand
happens
to
be.
The
rattrapante
hand
overlies
the
main
hand
in
movements
with
the
chronograph
mechanism
on
the
top
plate
(as
opposed
to
behind
the
dial).

As illustrated right,
we
see
the
rattrapante
wheel
(1),
its
small
heart
cam
(2),
the
cam
return
lever
(3),
and
the
return
lever
spring
(4).
Note
that
the
spring
is
actually
carried
on
the rattrapante
wheel
itself.
Because
the
rattrapante
heart
cam
is
carried
on
the
main
hand
pinion
(and
aligned
with
the
main
heart
cam),
a
“return
to
zero”
means
a
return
to
the
position
of
the
main
hand.

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As illustrated right,
we
see
the
rattrapante
wheel
(1),
its
small
heart
cam
(2),
the
cam
return
lever
(3),
and
the
return
lever
spring
(4).
Note
that
the
spring
is
actually
carried
on
the rattrapante
wheel
itself.
Because
the
rattrapante
heart
cam
is
carried
on
the
main
hand
pinion
(and
aligned
with
the
main
heart
cam),
a
“return
to
zero”
means
a
return
to
the
position
of
the
main
hand.

Traditionally
rattrapante
mechanisms
have
had a
major
drawback.
When
the
rattrapante
hand
is
stopped,
the
small
heart
cam
continues
to
rotate
with
the
main
hand.
The
pressure
of
the
rattrapante
return
lever
on
the
cam
places
a
significant
load
on
the
movement
for
as
long
as
the
rattrapante
hand
is
stopped.
For
this
reason,
the
rattrapante
heart
cam
is
usually
shaped
with
a
shallower
profile
(based
on
the
spiral
of
Archimedes
rather
than
a
logarithmic
curve).
While
this
lessens
the
load
on
the
movement,
it
does
not
eliminate
the
problem.

Right, this useful and clever piece of engineering is shown in greater detail. As the column wheel pivots the ratchet arm counterclockwise (illustration above), the ratchet arm pulls the return lever lifting wheel and its attached pin
(4) counterclockwise. The pin (4) hits the return arm (2) lifting it off the heart cam at
(3). The heart cam is free to rotate with the chronograph main hand. When the rattrapante hand is restarted, the return lever lifting wheel
(4) rotates clockwise and the return lever (2 and 3) acts on the heart cam
(1) to realign the rattrapante hand with the main hand.

RATTRAPANTE BRAKING

A rattrapante hand must brake instantly and precisely when the rattrapante mechanism is activated. Like most rattrapante designs, the Piguet design brakes the rattrapante wheel
(1) with a high precision scissors brake
(3 and 4) operated by the column wheel
(2). The column wheel acts on the scissors at the arrows. Brake activation and release are instantaneous, precise, and balanced.

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THE BALANCE ASSEMBLY

The Piguet chronographs all share the same balance assembly
(left), a three spoke Glucydur balance with KIF shock protection.

The fine regulator mechanism
(left) is an easy-to-use, low backlash, worm gear mechanism which is much more positive in action than the more common, friction-operated Triovis adjuster.

CONCLUSIONS

For originality of engineering and precision of chronograph function, the Piguet chronographs are without peer. For quality of workmanship, they are among a tiny handful of the very best, including those from Lange, Patek, Vacheron, and Audemars. Although more simply decorated than those of Lange or the Geneva firms, the Piguet finish, including functional finish, is immaculate.

Available in a variety of watches, most notably from Blancpain, the simpler Piguet chronographs can offer excellent values. The rattrapante–which carries a US$20,000 premium over the simple chronograph–seems inexplicably expensive. According to M. Humbert, former Professor of Special Chronograph Courses at the School of Watchmaking, Bienne (“The Chronograph: Its Mechanism and Repair”), the distinguished rattrapante return lever lifting mechanism may stem from an 1891 Swiss patent. Regardless, it is a wonderful refinement on the rattrapante mechanism and is, to my knowledge, available only from Piguet.