Montblanc Villeret 1858 Retour-à-Zéro Complication

Michael Ting (mkt33) delves into the technical intricacies of Montblanc's Villeret 1858 Grande Seconde au Centre Retour-à-Zéro complication, building upon a previous review by Art. This article focuses on the unique 'Retour-à-Zéro' function, a highly practical feature for precision-obsessed collectors, and compares Montblanc's approach to similar mechanisms from other esteemed brands.

Montblanc Villeret 1858 Grande Seconde au Centre Retour-à-Zéro - A Review of its Complication

By Michael Ting

© June 2010

Of all the mechanical complications out in the marketplace today, I cannot think of anything more useful than a “Retour-A-Zero” function.  For those of us obsessed with accuracy the ability to reset the seconds hand and synchronize it to a reference time source is invaluable.  

Of course many companies have taken advantage of this desire by putting out movements with similar complications.  

Lange & Sohne with their patented Zero-Reset mechanism.  

Glashutte Original incorporates this complication in their new chronometer with the Caliber 58-01 model.  

Chopard’s small seconds return to zero version is found in the LUC 10CF.  

And we can’t forget Panerai fans who also got their wish with a similar function found on the P.2002 movement.  

Although all of these watches allow their owners to reset the seconds hand to zero, their mechanisms of action are slightly different.  

It should be no surprise that a company known for its chronograph movements would fall back on its expertise and devise a “Retour-A-Zero” complication based on a chronograph.  

Montblanc’s Minerva Institut de Recherche created two calibers: 16-18 and 13-18 both with the same complication but for timepieces of differing diameters each in limited quantities.  

Caliber 16-18 is reserved for use in the Grande Seconde Au Centre Retour A Zero with a diameter of 47mm.  

While the Caliber 13-18 is reserved for use in the Seconde Au Centre Retour A Zero with a diameter of 41mm.  

Despite the slightly differing layouts, both movements are simplified chronograph mechanisms with only a reset and start function.  

The basic function mimics that of all horizontally coupled chronographs with the energy flow from the 4th wheel (which would carry the running seconds hand on a true chronograph) through the chronograph transfer wheel to the chronograph center wheel (which would carry the chronograph’s center seconds register hand). In the Montblanc R-A-Z this is continuously activated.  

 To reset the seconds hand to zero, the center wheel is uncoupled and a hammer descends on the heart shaped cam to turn the chronograph center wheel back to the zero position. The hammer stays on the heart cam holding the seconds hand at zero while the time is set. When the crown is pushed back in, the hammer is released, and the chronograph center wheel is coupled back into the energy flow, starting the movement of the center seconds hand.

The analogy is:
Pull the crown (brings the seconds hand to zero)=> stop and reset the chronograph
Push the crown back in (lets the seconds hand start)=> start the chronograph

The “hammer” on both of these calibers are distinguished by the “Minerva arrow”.    

Two issues to highlight.  

There is the assertion that horizontally coupled chronographs should not be left running continuously for fear of causing excessive wear and tear at the coupling wheels’ contact points.  

This concern is partially addressed by Mr. Cabiddu and Minerva’s design team when they modified the wheel teeth profile to a more epicycloidal shape.  This change, while not a new concept in horology, is an attempt to minimize friction at crucial contact points.  

(Photo: Dr. Magnus Bosse)

Also since both of these calibers use a horizontal coupling mechanism, the balance wheel is isolated and can freely swing uninterrupted when the crown is pulled to reset the seconds hand.  

This is important for Montblanc since the balance wheels used in the Villeret models are large and have a substantial moment of inertia.  

For the caliber 16-18, the balance wheel measures 14.5 mm and has a moment of inertia of 59 mg-cm2  

For the caliber 13-18, the balance wheel measures 11.4 mm and has a moment of inertia of 26 mg-cm2  

I will leave the actual physics up for discussion but in general the size/mass of the balance wheel and the oscillation rate both contribute to the stability and accuracy of a timepiece.  It is less likely that external forces will be able to disturb the frequency of an escapement which uses a larger balance wheel.  Similarly, the higher the oscillating frequency the less sensitive the escapement will be to external mechanical disturbances as well.  

(Photo: Dr. Magnus Bosse)

Since these Villeret calibers operate at the rate of 18,000 BPH, stopping or hacking the movement would adversely affect their accuracy since it would take a measurable amount of time for the mainspring and balance wheel to get back to their stable oscillating frequency (large moment of inertia, low beat). So by designing a Retour A Zero complication which does not disturb the escapement, Montblanc is able to preserve the advantages of utilizing a large balance wheel.    

Montblanc’s Retour-A-Zero is a simple and elegant solution wouldn’t you agree?    

In summary and for comparison:  

Lange- decentralized seconds display, vertical coupling, balance wheel stopped  

Chopard- decentralized seconds display, vertical coupling, balance wheel stopped  

(Photo: Edward Hahn)

GO- decentralized seconds display, vertical coupling balance wheel stopped  

Panerai-decentralized seconds display, vertical coupling, balance wheel stopped  

Montblanc- centralized seconds display, horizontal coupling, balance wheel free

Enjoy,

Mike

Copyright June 2010 - Michael Ting &  PuristSPro.com - all rights reserved

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Comments, suggestions, and corrections to this article are welcomed.