The Calibre 8541 Watches from IWC

The following pages are taken from "The Calibre 8541 watches from IWC. The ingenious harmony of 18 karat gold cases and legendary movement", code number A01686/01.91, dated October 1989. The document contains the operating instructions for the Reference 1850 and Reference 1876 and the details pertain particularly to those watches.

The components of the Calibre 8541. Knowing what's inside goes along with the understanding of its complexity - but we can't list all the work that went into it too.

The Calibre 8541 has the following features;

Diameter of movement 28 mm (12½ '"),
Height of movement 5.9 mm,
Decoration "Geneva Bar" and perlage,
25 Rubies,
Self-winding (IWC patent),
40 hour reserve when fully wound,
Barrel material: anticorrodal,
Mainspring, unbreakable, rustproof, antimagnetic (NIVAFLEX),
Shock resistant automatic winding mechanism (IWC patent),
Incabloc shock-absorbing system on the balance staff,
Antimagnetic, self compensating Breguet overcoil balance spring (first quality NIVAROX),
Extra-large beryllium balance, antimagnetic,
Oscillation frequency of balance: 19,800,
Eccentric drop adjustment,
Precision adjustment regulators via cam on index tail and micro adjustment timing weights on balance arms,
Manual setting and winding using the crown,
Regulation of watches in various positions and temperatures, based on the most stringent individual checks.

The Calibre 8541 works. It is a beautiful piece of watchmaking craft. The automatic winding mechanism - and the way it works.

Movement of the wrist causes the rotor to move through 360^o around its centre, a motion which it transfers to the automatic wheel 5. From there, it is transmitted via the pinion 6 to the crown wheel 7 and further to the ratchet 8 which winds up the mainspring 14.

The mechanism consists of four main component groups:

The rotor, to the underside of which the heart- shaped cam 1 is attached.
The rocking bar mechanism 15 secured by screw 16 to a cover. The mechanism consists of the base plate 15, the draw levers 17 and 18, the tension spring 19 which acts on both levers, and the two ruby bearing rollers 4.
The automatic wheel 5 and pivot 6.
And the shock absorption plate 20 which supports the rotor axis.

The reciprocal motion of the rotor and the main cam 1 which revolves around point 2 (fitted above and below with ruby bearings), are transmitted via the two rollers 4 to the rocking-bar mechanism 15 that (both sides in ruby bearings) rotates around point 21. The two draw levers - 17 with axis at point 22 and 18 with axis at point 23 -, of the rocking-bar mechanism, alternately transmit the see-saw movement of the rocking-bar mechanism to the automatic wheel 5 - with ruby bearings above and below - and provide the drive in the winding up direction. To ensure that the automatic mechanism reaches its full reserve period of over 40 hours and maintains the highest level of precision and perfection of function, the automatic watches must be regularly worn on the wrist. Naturally they can be manually wound up with the crown.

The rotor shock absorber system (IWC patent)

The shock absorption plate 20 with its spring arm 3 bears the axis of the rotor. With a shock or impact the rotor is able to swerve flexibly until the impact is absorbed by the watch case. The automatic winding mechanism is thereby completely protected against knocks the moment the watch is mounted in its original IWC case.

The calendar

There is an automatic change of date within a few minutes at about midnight (IWC patent). Adjustment of the date is done by moving the hands forwards or backwards - with no danger whatsoever to the mechanism.

Instructions for setting the date on watches with a calendar.

The date changes automatically between the 31st day of the month and the 1st of the following month. In months with less than 31 days the date is adjusted by the crown manually by moving the hands twice twelve hours forward. Should it be necessary to correct the date by several days the hands must be set to midnight and the minute hand must then be moved between 23.45 and 0.15 hours. With every forward movement the date moves on one day.

Equilibrium of the balance spring.

The centre of gravity of a well-centered balance spring is virtually at the axis. While the balance is in motion however, the spring changes its shape and dimensions.

The eccentric movement causes the mass of the balance spring to shift, thus creating a point of balance which is constantly changing. When the watch is in certain positions, this leads to a loss of accuracy.

The Breguet overcoil balance spring (spiral breguet).

Named after Abraham Breguet, the celebrated watchmaker. On this spring the outermost coil is curved upwards so that it runs parallel to the other coils. This outer coil has a special shape (the Phillips end curve).

The spring used in high precision watches, is concentric. Forming these coils is an extremely skilled task calling for a sharp eye and an instinctive "feel". For this reason specialists - known as "regleuses" are employed - women who have completed a two year apprenticeship in spring processing.

Regulating.

The initial regulation is done by moving the mobile head 24a of the two part regulator 24.

Precision regulating.

The regulator 24 can be carefully shifted by using the eccentric 25. By this means inaccuracies of up to 10 seconds every 24 hours are easy to correct.

Micro-regulating.

Should an even more precise regulation be required, the small weights 26 on the balance can be turned by means of a screwdriver (always kept parallel). These weights are not screwed, but mounted on pivots and therefore turned with ease. One half of the screw head is bevelled off.

If the watch is fast, the weights are turned so that their heavier half is further away from the centre of the balance.

If the watch is slow, the process is reversed. With practice it is possible to carry out corrections of as little as 5 seconds. Thanks to the Incabloc shock absorption system these corrections can be undertaken at the movement itself - without having to remove the balance.

IWC's drop adjustment system.

By turning the eccentric 27 the stud support 28 is released and this can then be shifted to facilitate precise adjustment of the drop. Now you know automatically how it is possible to reproduce the time mechanically.

From the IWC publication A01686/01.91, October 1989, pages 16 to 19.

If you would like to learn more about the Pellaton winding system, please click on the following article from the same publication.

Pellaton Winding System

Satoru Yoshida was kind enough to provide a PDF copy of the full article in May 2006

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