Tribute to the Great Explorers - A View from the Inside

NB. First a minor alert!

Some of the following is a bit technical and you will have to refer back and forth to the images and video to help your understanding. You might also have to enlarge some of the photos to see the details.
Hopefully there won't be too many eyes glazing over. wink
As the French say: "C'est parti!" (On with the show!)

I was recently in New York City at the Vacheron Boutique, to pick up my “Tribute to the Great Explorers” watch which had required some minor adjustments. This got me thinking about the movement which powered the watch and the mechanism which provided the hours and minutes. The attributes of this marvellous watch with its beautiful dial using “grand feu” technique has been presented previously.

Tribute to the Great Explorers - A View from the Inside   Tribute to the Great Explorers - A View from the Inside

However, I wanted to look more closely at the actual mechanism. The design is a real break from the traditional display of time and as many of you know, the concept of alternative displays has fascinated me for many years. The “star wheel” concept, which this watch employs, has been used in the recent past by both Audemars Piguet and Parmigiani Fleurier in their own watch designs. But the concept itself goes back to the beginning of the 19th century.
( A caveat: All the explanations are my own based on my brief study of these watches. They may not be 100% correct. I, of course, invite any corrections.)
The “Star wheel” concept was first presented by the Perrin Frères of Neuchâtel who produced a pocket watch around 1800 containing this type of mechanism. It uses a clever planetary gear design with rotating numbers to indicate the time.

Tribute to the Great Explorers - A View from the Inside

Tribute to the Great Explorers - A View from the Inside
Perrin Frères pocket watch showing the case and dial window, and the movement with its planetary gear,
3 “planets” each having 4 “moons”.

Thomas M of the Purists mentions in his review of the AP watch that the design was from the Vaucher Frères which initially made sense since they were quite innovative and were one of the first to design a “Bras en l”Air” watch. But I could find no references, articles or photos to support this contention.

The design of the Perrin pocket watch featured a central hub with three equidistantly placed hubs, 120° apart and each with four numbers. As the central hub rotates the planetary gear, the numbers at the ends of the arms also rotate along with it. They also rotate independently in a specific manner to display the correct time in a crescent-shaped window of about 120 degrees. (I will discuss the mechanism and its evolution or should that be “revolution” further in the article.)

Unfortunately the photos of the Perrin module are low-res jpegs, which do not allow clear visualisation of the details, especially in how the number discs rotate. I could find only a few general explanations of the mechanism, none of which explained it properly or completely. It looks as if there are two, possibly three pawls which engage the gear wheel under the numbers hub causing to rotate it the appropriate amount so that the correct hour number displays vertically as it transit the display window.  Parmigiani Fleurier restored the watch around 2010 and it was part of their display of alternate watches in New York City in 2011. It also inspired the production of their own watches, a pocket watch (Toric Repeater) and a wristwatch with a similar display. The wrist watch, called the “Capitole”, also has a repeater module. I could only find photos of the dials. I can only assume the mechanism is similar the Perrin design.

Tribute to the Great Explorers - A View from the Inside

Then in 1991, Audemars Piguet produced a Star Wheel watch using their Calibre 2124 movement (according to Audemars Piguet by Brunner, Pfeiffer-Belli and Wehrli) although Thomas M  credits the Cal. 2224/2811) and a planetary module to change the hours.  The watch was produced in a  limited addition of 250 for Audemars-Piguet 125th anniversary. The mechanism involved three sets of sapphire discs. Each disc has four numbers, in intervals of three ie; 1,4,7,10; 2,5,8,11 and 3,6,9,12. Thus the correct sequence would follow with proper rotation of the number wheels. The planetary gear rotated once every 3 hours; therefore each sapphire wheel would present one number, in sequence, once during every rotation, for example “1” from the first disc, then “2” from the second and then “3” from the third. The challenge was to rotate the individual sapphire discs before the number was displayed in the window.

Tribute to the Great Explorers - A View from the Inside

Audemars did this by having the discs mounted 120 degrees apart and under each was an 8 pointed star wheel. Mounted at each of the apices of the arms was a curved cam to which are attached pawls. Each cam/pawl combination controls the 8 pointed star wheel clock-wise from it. At given points in the 360° rotation of the planetary gear, the pawl engaged the teeth and pushed it counter-clockwise one tooth.  The angle between any three teeth points of this tiny star gear is 90°. The middle tooth cuts this angle in half to 45°.

In the photo on the right, below, you can see that the end of the pawl forms a right angle tooth that engages between two teeth of the little 8 point cam and pushes it 45°. I believe that the cam/pawl combinations work in pairs rather than all three together, so that the angle change is of a given disc is 90°. The specific pawl attached to the disc with the number displaying the time should naturally not  move during the transit time across the display window. There is likely some mechanism under the star wheel that engages with the cams causing them to push the pawl causing the tooth and the sapphire disc to rotate appropriately.

Tribute to the Great Explorers - A View from the Inside
Left: Sapphire disc with numerals: 3,6,9,12
Middle: Ovoid cam with pawl engaging star wheel
Right: Eight point star wheel with Teflon bushing

Tribute to the Great Explorers - A View from the Inside
Two other views of the planetary gear, cam/pawl 8 point star wheel, and sapphire discs.

The difficulty in this design is the very close tolerances required because of the loads put on the movement. This was not a “jump hour” watch but one in which constant rotation of a relatively heavy planetary gear and disc rotations twice/hour were present. A robust movement was therefore required.

Audemars re-released the design in their Millenary series in 2000 also in a limited edition with the same module, probably with better manufactured tolerances. They also released a pocket watch with the time on one side and a star wheel on the other which indicated the months and days. (below)

Tribute to the Great Explorers - A View from the Inside    Tribute to the Great Explorers - A View from the Inside

                               Tribute to the Great Explorers - A View from the Inside

What I believe to be the culmination of this design concept was attained by Vacheron Constantin in their release of the Tribute to the Great Explorers series. Not only does the dial, a wonderful concept in its own right, elevate the watch from a utilitarian appearance to a work of art; but the redesign of the star wheel module makes it more stable and moves the torque loads to the centre of the module from the periphery (More about that later).
Firstly, the choice for the movement of this watch was Vacheron’s Calibre 1126, derived from JLC’s reference 889. It is a robust movement which Vacheron has used in its Overseas model as well as some Retrograde models. There is an excellent technical review of this movement by Jack Forster and here is the link.

The important piece of this watch’s movement, of course, is the star wheel module. In the exploded view seen below, which I have partly labeled, one can see the relevant parts.

Tribute to the Great Explorers - A View from the Inside
Exploded view of movement

In the centre is the planetary gear marked as (A). It has 3 arms set 120° apart. Beneath the centre is the drive gear connected to the Cal. 1126. On each arm is a small bushing on which is mounted the tiny 8 pointed cam, which looks a bit like the  Maltese cross (C) Vacheron logo.  And above it is a 32 teeth reduction gear (RG1).

There are 3 small bushings on the on the periphery of the planetary gear which are at the ends of the 3 arms. On this is mounted the second reduction gear with 64 teeth. It will mesh with RG1. On top of this gear (RG2) is the disc holding the hour numbers, four per disc, spaced 90° apart.
In the centre of the Planetary Gear (A) is a most important part, the central cam (B). It does not rotate, but note that it is oriented with its smooth side down. If you draw a line between the ends of the smooth sections of the cam, you will divide it in half. That line is also parallel to a line between the ends of the minute disc. This orientation is crucial. (See free-hand drawing below)

The cam itself has a smooth part in its lower half, as mentioned, which is a semi-circle of 180°. The upper half consists of two sets of 2 U-shaped cut-outs on either side of a vertical prong separated by a smooth section. If you look closely you can see that each set of cut-out is separated from the upper smooth section by 60° and thus all 3 parts occupy the other 180° of the circle.

Tribute to the Great Explorers - A View from the Inside
Watch with upper dial removed to show layout of movement.

Tribute to the Great Explorers - A View from the Inside
Tracing of central cam and minute dial with angles drawn in.

One other important point: The little Maltese cross cam has four arms, each 90° apart. The space between the 2 points of each arm is a concave arc, which matches the convex curvature of the central cam exactly. In the photo below, you can see the cam quite clearly. Through the magic of Photoshop, I have removed part of the numbers “1” and “12” which were partly obscuring the details. Here you can see all the parts of this cam described in the previous paragraph. Unfortunately the Maltese cross cams are obscured by the 32 teeth gear wheels. (below)

Tribute to the Great Explorers - A View from the Inside

I may be belabouring the obvious, but these relationships and angles are very important once the movement gets going.

As the planetary gear rotates, the Maltese cross cam on the left comes in contact with the first cut out of the central cam. It locks and then rotates the small cam 90° clockwise. The 32 teeth gear sitting on top of the cam (C) rotates clockwise as well, meshes with the larger 64 teeth gear and reduces the rotational angle in half to 45°. This gear, of course, rotates counter clock-wise and causes the number disc to rotate 45° as well. The Maltese cross cam is locked in position with the curve between the points sliding along the curve of the central cam for 60° until in meets the second cut-out and is then again rotated 90°. The number disc is also rotated but again by only 45° counter clock-wise. The last rotation is completed just as the number reaches the horizontal gold line defining the edge of the enamelled minutes dial. The total rotation of the number disc is thus 90° which puts it in a horizontal orientation with respect to this dial.
The Maltese cross cam is now positioned so that its convex curved part (between 2 points) contacts the lower concave curve of the main cam. It simply slides along this curve as the planetary gear rotates and traverses the 180° until it reaches the other gold edge of the dial on the left. No further rotation of this number disc can occur during this 180° traverse.
Since the number discs are mounted 120° apart the next number in the correct sequence will cross the “0” minute mark just as the number ahead of it crosses the “60” minute mark. The spaces on either side (30° each) are hidden by the top part of the dial.
The animation linked below shows this progress well but has to be watched several times to really grasp the sequence of events.

Keeping an eye on the number disc with the numeral “10” will help to understand the interaction of the Maltese cross cam with the main cam, especially the CCW rotation of the “10", and just above it how the number “7” comes into proper alignment.

Furthermore, one can conclude that because the planetary gear rotates once in three hours, and each of the three number discs rotates 90° counter clockwise during the rotation of 3 hours; then in 4 rotations, or 12 hours, each number disc will rotated 360° bringing it back to the original position to start the next 12 hours.

Now, just a few words about the enamelled minutes dial. If you examine the line between the minute numbers, it looks as if there is more space between them at the “0” end than the “60” end. This arrangement makes it look as if the hour number will initially have to move faster at the beginning and slow down near the 50-60 minute portion. But it is only an illusion. These lines converge on the compass rose on the upper dial, which is actually positioned above and along the path of the planetary gear and coincides with the centre of the number disc as it passes the 50 minute mark.
If you draw lines from the centre of the “0” and  the  centre of the numbers to the centre of the main cam, they all subtend an angle of 20°, which makes perfect sense since 6 x 20 °= 120°. Thus the movement of the planetary gear is constant at 2° per minute.

However, the numbers indicating the minutes on the dial are slightly skewed. The numbers are positioned in this manner in order to align the passing hour number correctly with the minutes as it passes over them (a small but important touch).

Once you understand the workings of this module, the knowledge can only enhance the appreciation of this watch. It is not only the beautiful two-layered dial which makes this watch a fantastic accomplishment, but the movement below the dial, brilliantly conceived and executed that makes the this piece most worthy of the “Metiers d’Art” designation.

In the future, if Vacheron is contemplating another release of a set of Explorer watches, they might consider looking at the early explorers of the heavens. Ptolomei, Galileo, Copernicus and Kepler come immediately to mind. But there are many others. It seems only fitting given the use of a "planetary" gear wink

Re: Tribute to the Great Explorers - A View from the Inside
04/28/2014 - 03:53
Oops! I clicked the "post" button a little prematurely. I owe a real thanks to Jack Forster for his fine article on the Calibre 1126; Thomas M and the Purists site for his review of the AP Star Wheel watch; and to Alex for his great article on the VC Great Explorer posting here on the Lounge and for his great photo of the inside of the movement which helped considerably. Joseph
I'm speechless,
04/28/2014 - 15:01
so therefore I write smiley What a great work you have done. The only problem is that because of your writing I have realised that I need one of those watches (sigh). I really like that you have included so many links and references. After reading your article I feel wiser. I have added a photo from page 140 from a book called " AP Audemars Piguet Le maitre de L'horlogerie depuis 1875" written by Francois Chaille. This is what they write about the Star Wheel. In that book they refer to these movements on the following pages. Caliber 2224/2812 for the Ref 25720BA. Caliber 5020/2817 for the pocket watch with ref 25743BA (not the one with two dials). Cal 2867 for the ref 25881OR (J. Shaeffer model with minute repeater). Don't know if it is relevant but maybe there is something relevant for your research.   For music listening to accompanying the reading of the your latest addition I chose Don Juan, Till Eugenspiegel and Death and Transfiguration by R. Strauss recorded by Szell and The Cleveland orchestra and while listning and reading I visualised a young Joseph in the audience. With warm regards, Kent
Thank you very much, Kent
04/29/2014 - 17:04
And thanks for the info on the Schaeffer watch. I did know about it but decided not to include it since the movement was basically the same as the other two AP watches. There is a really nice photo of it from a Christie's auction a few years ago and Ihave included it here. As for the music, the only time I ever saw Szell and the orchestra in Toronto, I don't believe Strauss was on the programme smiley I think I would have preferred Gustav Holtz's "The Planets" Best wishes, Joseph
Amazing journey through
04/28/2014 - 16:32
this Typology, thank you. A little question on a marginal aspect, I knew calibre 1126 used for this particular kind of affixion, derives from JLC 888 instead of 889 but I'm probably wrong. Thanks again.
Many thanks for your kind words!
04/29/2014 - 17:06
I did check on the JLC reference and my references did confirm that it was their Cal. 889 Best, Joseph
What a fantastic psot Joseph
04/28/2014 - 18:01
Loves the way you wrote through the technical path to show the wandering hour system thanks a lot for this post ! Cheers François
Thank you, François
04/29/2014 - 17:08
I am very pleased you enjoyed it. It was a bit of a challenge to explain it without making it too complicated. Regards, Joseph
I really like your idea for extending this complication...
04/28/2014 - 18:13
with some other astronomically themed dials!! Thank you for the essay: it has enhanced my appreciation for the Great Explorer set. Bill
Very interesting Joseph
04/28/2014 - 18:35
Thanks for taking the time to present the artistic and technical merits of these wonderful watches smiley
My pleasure, Dean
04/29/2014 - 17:15
I'm delighted that you found it interesting. It is a watch that is a beauty to observe and I think an understanding of the design enhances one's appreciation of it. Regards, Joseph
Thank you, Bill
04/29/2014 - 17:10
It's a fantastic watch and I owe you a debt of gratitude for thinking of me in the past regarding it. Best wishes, Joseph
Re: Tribute to the Great Explorers - A View from the Inside
04/28/2014 - 18:41
JB, are you sure you are not in the watch business? I mean how on earth do you manage such wonderful research? You and one-two more loungers could give the industry a run for its money in terms of knowledge and history.  While I have not read this article as yet, I can see that it is definitely well researched and put together. I wonder what happnes to watch retailers when the likes of you (and you) enter a watch boutique? After a few minutes, they must want to run for their lives.  Truly well done.
Thank you so much, kk!
04/29/2014 - 17:13
I hope you will enjoy it. Vacheron did a fantastic job with and I was trying to enhance that aspect in the article. Regards, Joseph
what can I say Joseph? You did it again, interesting and
04/28/2014 - 19:44
educational read. I would also add Urwerk to your article, they brought out thair 101 with rotating discs about the same time as the Great Explorers
Thank you Alex
04/29/2014 - 17:19
And thanks for the Urwerk. An unusual and appealing design. I would describe it a "neo-robotic" wink It would be interesting to see what's under the hood! Thank you also for taking the time to get those photos especially the last one. All the best, Joseph
A path of discovery...
04/29/2014 - 18:11
Joseph, I've had a stroll, and taken a few breaks, whilst feasting my eyes and mind upon your array of copy, graphics and photographs. Whilst I cannot claim to have absorbed all that is on offer, be assured no stone will go unturned during my subsequent visits. Your editing skills are worthy of recognition - you had alot to say. including a number of added links, and it was crucial to maintain a balance plus a strong thread of continuity. That you most certainly achieved! Unquestionably, projects of this type take a great deal of research and time. I am indebted to you for a wonderful contribution. On that point I can't imagine what you've got inmind for the future. Whatever it is we have much to thank you for in the Lounge. With kind regards Tony 
Re: A path of discovery...
04/30/2014 - 17:16
Thank you so much, Tony, for your very kind comments. They are most gratifying. As for the future, well, I have a few ideas... All the best, Joseph
An Amazing reference post JB! Thanks Again.
04/30/2014 - 09:13
Hi Joseph,  this is a great piece of research/learning about the Great Explorers watches and their history. I've copied it over to a file to use as reference, even when I'm offiline :-) BR, Dan
Re: An Amazing reference post JB! Thanks Again.
04/30/2014 - 17:20
Thank oyu very much, Dan. It took some time to figure it out and I'm sorry i couldn;t be more specific about the earlier watches. Sometimes information is just not available on line, believe it or not wink. Short of visiting Parmigiani to see the Perrin watch and their own design, I could fine no specific info. Oh well, at least VC was more forthcoming and in fact has the best design for the star wheel concept. Their engineers should be very proud! Best, Joseph
A favorite topic, Joseph
04/30/2014 - 17:58
You know the way to my heart.  heart I love alternative time displays, as you probably know.  The AP Starwheel is, I think, the watch that really got to me first, and I still admire that watch so much.  I think VC improved upon the movement design to create a better performing and more robust mechanism.  Thank you for explaining all of the technical details so that even I can almost understand.  frown I love your final idea for a next set of Explorers watches paying tribute to the explorers of the heavens.  I hope VC takes up this suggestion.  What a great article and contribution to THL. Best regards, respo
Re: A favorite topic, Joseph
04/30/2014 - 23:04
Thanks very much for your kind words, Robert. Yes, it would be great if VC had a series on the explorers of the heavens. Are you listening, Vincent and Christian?? Joseph
Sign me up for a 'Copernicus' ;-) great technical detail in your story
05/02/2014 - 00:26
Joseph. I knew about the Starwheel AP, just didn't realize the importance of the watch. Thanks for sharing your knowledge, JB!
Re: Sign me up for a 'Copernicus' ;-) great technical detail in your story
05/02/2014 - 21:37
Thanks Radek for your kind words. I'm glad you enjoyed it. You can out me down for a Copernicus too! Best, Joseph