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Patek Philippe - In The Fast Lane With Patek Philippe (Part 2/3)

Patek Philippe In The Fast Lane With Patek Philippe (Part 2/3)

Precision, precision, precision! The three words defining the development of the cal. CH 29-535 PS 1/10 that drives the Patek Philippe ref. 5470 1/10th Second Monopusher Chronograph

Previously, we covered the technical basics of the Patek Philippe ref. 5470 1/10 Second Monopusher Chronograph, with a recap of the timepiece's background and how to actually interpret the novel display, which gives chronograph readings with tenth-of-a-second precision. On this very note, there’s no point incorporating a high-frequency, high-precision balance without having an equally high-precision mechanism that is able to translate the 10 beats per second of the 5Hz (36,000vph) balance into a crisp, error-free reading. Today, we're going to find out how the ref. 5470 does it, starting with the mechanical engagement of the chronograph in the CH 29-535 PS 1/10.

Patek Philippe ref. 5470

The stacked wheels to the centre-left of this image represent the mechanical engagement point of the chronograph in the cal. CH 29-535 PS 1/10 © Patek Philippe

Conventional chronograph mechanisms understandably prioritise security in gear engagement, which necessitates using gear teeth of limited geometry in the intermediate chronograph wheel, usually of pyramidal profile (rather than involute form) in order to minimise the possibility of gear misalignment at the moment of engagement. The cal. CH 27-70, predecessor of the CH 29-535 PS, operated on this very principle and was considered an extremely successful chronograph movement for decades. The downside of this kind of construction was reduced precision in the motion of the chronograph seconds hand, resulting in a chronograph seconds hand with visible back-and-forth flutter (known as backlash) and loss of display accuracy. This was usually compensated with large amounts of fine adjustment in gear engagement by the watchmaker (a time- and labour-intensive process), or by adding a tension spring on the chronograph seconds hand (thus raising the energy consumption of the chronograph) — both sub-optimal solutions, as you can easily imagine.

In theory, gear teeth can be designed to mesh with perfect tension and engagement. In practice, there is usually a small gap factored in to ensure that the teeth do not jam at their tightest point of engagement.

Patek Philippe ref. 5470

In practice, geared wheels are deliberately spaced so that the teeth do not jam at their tighest point of engagement © Douglas Wright, University of Western Australia

This gap can result in tiny imprecisions in the motion of all components further down the line of gear transmission. While this is acceptable in virtually all uses of mechanical gearing, the strict standards of watchmaking at Patek Philippe meant a better solution had to be found for the cal. CH 29-535 PS 1/10. Ideally, the gear teeth of one of the wheels would be able to reactively widen and narrow themselves in order to form perfect engagement at all times with the other set of gear teeth, compensating for microscopic variations in gear engagement and near-invisible manufacturing errors.

Patek Philippe ref. 5470

One example of split-tooth gearing, found in the chronograph engagement of the Rolex Daytona (The shiny surfaces and extra-fine details are typical of parts formed through LIGA microfabrication techniques) © Rolex

Some modern chronographs use the split-tooth gear profile made possible by high-tech microfabrication techniques such as LIGA, creating a one-stop solution that reconciles the need for secure gear engagement with an elevated level of display precision, without compromising on production or energy efficiency. For the CH 29-535 PS 1/10, Patek Philippe movement developers chose to implement their own take on flexible gear toothing, a tried-and-tested approach for anti-backlash gear engagement.

Patek Philippe ref. 5470

Another example of split-tooth gearing, developed by Geneva movement maker Agenhor © Agenhor

To achieve this, two chronograph driving wheels with identical gearing are superimposed on the same axis, the upper wheel equipped with flexible arms so it is able to accommodate the tiniest fraction of rotational displacement from the lower wheel, which has rigid arms and turns strictly in accordance to the fourth wheel in the going train (also on the same axis, just as it would be in a conventional chronograph). Despite being two distinct components, the dual chronograph driving wheels function as a single unit, their stacked gear teeth working together to mesh perfectly with the tenth-of-a-second chronograph wheel. The slight amount of rotational play between the two chronograph driving wheels, sprung to maintain constant tension, allows for the reactive gear tooth profile described earlier.

Patek Philippe ref. 5470

The anti-backlash dual-wheel system of the cal. CH 29-535 PS 1/10, assembled (left) and disassembled (right) © Patek Philippe

Patek Philippe ref. 5470

A close-up view of the anti-backlash dual-wheel system of the cal. CH 29-535 PS 1/10, showing the small angular displacement between the two stacked wheels © Patek Philippe

Patek Philippe ref. 5470

Animation demonstrating how the dual-wheel anti-backlash system works (yellow upper wheel, pink lower wheel) to create an ideal engagement Original animation © Douglas Wright, University of Western Australia / Modifications © WorldTempus

This expertise in flexible steel components can be directly traced back to yet another Advanced Research project from Patek Philippe, the 2017 ref. 5650G Aquanaut Travel Time. This timepiece established Patek Philippe’s ability to fabricate sophisticated compliant systems in traditional materials such as stainless steel, and we continue to see the impact of this savoir-faire in the ref. 5470 1/10th Second Monopusher Chronograph.

Patek Philippe ref. 5470

Patek Philippe gained expertise in compliant systems (visible through the dial cutout) through their work on 2017's ref. 5650 Aquanaut Travel Time Advanced Research © Patek Philippe

Completing the journey of precision for the tenth-of-a-second chronograph mechanism is the chronograph tenth-of-a-second pinion. For maximum precision in engagement — which, as you can imagine, is incredibly important for a reading of such accuracy — the pinion has 136 teeth, each measuring 30 microns in depth, over its 1.469mm diameter (meaning a circumference of just over 4.6mm). There is a fine line between mechanical gear engagement and friction engagement, and the teeth on the chronograph tenth-of-a-second pinion are so small (requiring LIGA microfabrication techniques) that we might as well be talking about a friction engagement here.

Patek Philippe ref. 5470

The teeth on the pinion of the tenth-of-a-second chronograph hand (indicated by the blue arrow) are so fine that the pinion appears to be perfectly smooth and round to the eye Original image © Patek Philippe / Modifications © WorldTempus

Patek Philippe ref. 5470

Magnified view of the extremely small teeth on the tenth-of-a-second chronograph hand pinion on the cal. CH 29-535 PS 1/10 (Computer rendering) © Patek Philippe

The Patek Philippe movement developers also devoted considerable effort to the red chronograph seconds hand that indicates tenths of a second in the ref. 5470. As it required lightness and rigidity, the natural choice was to make this hand in Silinvar, Patek Philippe’s proprietary term for silicon with a layer of thermo-compensating silicon oxide. However, Silinvar is a dark silvery bluish-grey, and the Patek Philippe team wanted a brightly coloured hand for legibility.

The very qualities of Silinvar that made it an ideal material in regulating organs — low-friction surfaces, hardness, low chemical reactivity — made it a nightmare to colour. How do you make colouring agents stick to a material that is known for its near-zero surface porosity, a material that looks perfectly smooth even at magnification levels of several thousand? Patek Philippe ended up patenting a novel process for this purpose, using PVD (physical vapour deposition) or CVD (chemical vapour deposition) to first coat the Silinvar hand with a thin primer of metal oxide that subsequently provides an adhesive surface for the red lacquer paint.

Patek Philippe ref. 5470

The red lacquered Silinvar tenth-of-a-second chronograph hand on the ref. 5470 © Patek Philippe

It is perhaps futile to try and cover every single aspect of the ref. 5470 and the cal. CH 29-535 PS 1/10 in the realms of precision timekeeping and time-display. However, something that any one of us can immediately observe just by looking through the transparent caseback of the watch, is the extraordinary number of eccentrics that are visible — telling us that while the construction of the cal. CH 29-535 PS 1/10 is based on the values of precision and reliability, there is still a vast built-in capacity for manual intervention, which permits limitless adjustment towards that mechanical ideal — the perfect chronograph.

Patek Philippe ref. 5470

The blue arrow indicates an example of an eccentric, which allows for high levels of manual adjustment in the mechanism. Numerous other such eccentrics can be identified around the cal. CH 29-535 PS 1/10 Original image © Patek Philippe / Modifications © WorldTempus

One last point on precision: Tucked away underneath the mobile chronograph bridge, outshone by newer, more exciting mechanical innovations is a (literal) quiet hero — a ball bearing pivot. Whereas more conventional chronographs in the fine watchmaking category use simple bushed and jewelled bearings in this component, such bearings allow small amounts of mechanical play in various directions, once again leading to undesirable loss of precision.

Patek Philippe ref. 5470

The blue arrow points to the ball bearing pivot of the mobile chronograph bridge Original image © Patek Philippe / Modifications © WorldTempus

Mounting the mobile chronograph bridge on a ball bearing eliminates all unwanted motion of the intermediate tenths-of-a-second chronograph wheel, and is furthermore space-efficient, providing the best possible ratio of component stability relative to its size.

Did someone say “stability”?

If you missed part 1, click here.

NEXT: How the Patek Philippe ref. 5470 1/10 Second Monopusher Chronograph protects its most vulnerable components


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