The Patek Philippe Caliber 27-460

by Walt Odets

The Swiss have been producing regular-production automatic movements for about half a century.  If there is a single  automatic movement
that stands out as the reigning queen of that half century, it is the Patek Philippe caliber 27-460 and (with simple calendar) 27-460 M.  In concept, in construction, and in finish, this is perhaps the most
elaborate and costly simple automatic watch movement ever produced.

Patek began production of automatic movements somewhat later than most other manufacturers.  It was 1953, and Patek released the 12-600 AT, a
lavishly conceived, if not quite perfected, attempt at the highest possible quality in an automatic.   A number of problems developed with the complex winding system of this movement, requiring the addition of
a ball bearing and two jewels.  The movement, finally, also received a Gyromax balance wheel and to keep it (and its massive 18K winding rotor) in place, an additional attachment to the case (for a total of three).

Seven years later and most problems solved, Patek re-released the movement as the caliber 27-460 and, a year later, the  27-460 M.  This iteration of the movement replaced the jeweled winding rotor bearing
with a slightly flatter ball bearing and a unique adjustable balance spring stud carrier.  The 27-460 was otherwise unchanged from the later versions of the 12-600. 

By today’s standards for high-grade calibers, the 27-460 is massively overbuilt: 12 lignes (27mm) and 4.6 millimeters thick without calendar, an even
heftier 5.35 with.   The 27-460 was to remain in production as the base movement for the perpetual calendars for 25 years until finally replaced in 1985 by the much flatter caliber 240.  


The basic movement of the 27-460 (right, central rotor removed) is designed very much in the tradition of Patek’s lovely hand-wound calibers.  
Separate bridges (really, cocks) are used for balance (1), escape (2), and fourth (3) wheels.  Shock protection is provided on the balance and lower escape wheel pivot.  The
upper escape wheel cap jewel uses a traditional, removable black-polished plate to retain the upper cap jewel (below, left).

A single, large bridge (4) carries the upper pivots of the third and center wheels, the central winding rotor ball- bearing mount (5
), and two super-bridges (6 and 7) for the extremely sophisticated automatic winding mechanism.  The entire construction is, of course, rhodium plated, and finished to the standards of the Geneva
Seal.  The Geneva seal appears both on the mainplate (8) and the winding super bridge (7).   It is customary to place the seal on both the mainplate and one bridge, usually the crown wheel
or barrel bridge.


The movement designer is always in pursuit of maximum balance diameter and adequate diameter for the mainspring barrel for power reserve.  As can be seen in the stripped
top plate (right), the 27-460 is amply provided for in both cases.  The balance (1) occupies about 35 percent of the diameter of the movement, the mainspring about the same.

The 27-460 (unlike the
earliest versions of the 12-600) uses Patek’s Gyromax, adjustable-mass balance with a Breguet over coil spring (right).  The overcoil itself is indicated at the arrow.  The rotatable Gyromax rim
weights permit poising of the balance, as well as adjustment of daily rate.  This arrangement eliminates the conventional regulator index, with all the positional adjustment problems it poses.





On the caliber 27-460, Patek introduced another extremely useful innovation, the “self-adjusting” balance spring stud carrier (above and below right).  A lock
screw on the top of the balance cock may be loosened once the cock, balance, and spring are in place on the top plate.  The stud then moves into any position necessary to allow the spring to perfectly center
itself.  Centering is the key to good positional performance, and no other stud design assures such perfect centering.  Beat error, unfortunately, must be corrected by  the traditional, tedious method of
rotating the inner spring attachment (collet) at the balance staff.



Although the 27-460 was destined to serve as the base for Patek’s illustrious perpetual for a quarter of a century, the caliber 27-460 M
offers a simple guichet date at three o’clock.   As illustrated left, the construction of the mechanism is as elegant as the rest of the movement.   The calendar wheel (1)
rotates a cam beneath it.  A fully finished arm (2) with bronze roller and fabricated spring provides instantaneous change at midnight.   There is no provision for quick setting of the
date.The lower shock protection for the escape wheel is shown at (3) and the conventional, but extremely well-made, keyless works at (4, above) and center left.








While most calendar mechanisms use a simple bent steel spring to detent the calendar disc, the 27-460-M uses a beautifully
machined detent and cut, finished spring.  This mechanism is comparable in quality  to Patek’s more complex perpetual plates and is surely the most elegant simple calendar ever constructed.


To date, the automatic winding mechanism of the 27-460 is Patek’s only fully successful attempt at a bidirectional-winding system.  In a subsequent attempt at a thinner bidirectional system, Patek produced the
caliber 350, a backwind, planetary gear design that proved troublesome throughout its life.  In 1970, Patek resorted to use of the caliber 28-255 in the Nautilus, a JLC ebauche shared with Audemars Piguet and
Vachercon Constantin.  Patek continued with this JLC ebauche until the introduction of the caliber 335SC  unidirectional winder in 1980.

The entire automatic winding system is contained on the “main bridge” of the movement, which also supports the upper pivots of
center and third wheels.  The bridge is shown right, stripped of all mechanism.   The arrow indicates the lower pivot of a ball bearing supported eccentric wheel that is driven by the
winding rotor and rides inside the arms of a rocker.


The rocker (right, 1) is driven by the eccentric wheel between its arms (2).  Rocking on a jeweled pivot (3
) the rocker carries a click-pawl.  By means of a lobe (5), the rocker also drives a second rocker with its own click-pawl (6).

As seen mounted under their bridge (left), the function of the rockers and click- pawls may be understood more clearly.

The first rocker (
1) carries its own click-pawl (5).  By means of its lobe (1A), the rocker drives the second rocker (2) with its click-pawl (3)  through a jeweled interface (4
).  Each of the two click-pawls alternately winds and holds the first drive wheel (6, moving counterclockwise).  A single bridge (7) holds all components in jeweled
bearings.  In operation, the rockers and click-pawls play an uncanny, rapid-fire, syncopated choreography.

The pair of square jewels on the second rocker (to interface with the lobe of the first rocker) are typical of the wonderful construction seen
throughout the caliber 27-460.  In this 40 year old example of the caliber, the original automatic winding parts showed virtually no wear.


Although an early effort in the history of automatic wristwatches, the Patek caliber 27-460 has never been improved upon in terms of robustness, elegance of concept,
or fineness of construction.  Thinner, more efficient, and less expensive designs have surely followed, including the excellent current Patek calibers 240 and 315.  But, with the probable exception
of the recent Lange caliber L921.2, no automatic wristwatch caliber to date has  equalled the unbridled pursuit of quality evident throughout the wonderful 27-460.  It is a masterpiece of