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orologicalournalHJ

March 2009

In Breguet's Footsteps...Derek Pratt FBHI describes double wheel escapements.

106 March 2009 Horological Journal

When Abraham Louis Breguet made thefirst ever tourbillon, No. 282, in the earlyyears of the 19th century, he used anArnold spring detent escapement. Later,he modified a John Arnold watch, whichhe then returned to its maker fitted witha tourbillon carriage and Peto cross-detent escapement. Although this watchwas converted a few years after No. 282was made it had a lower number, 169.

Detent escapements impulse thebalance only once per oscillation, whichis not ideal for a portable timekeeper. Atthis time, Breguet was experimentingwith escapements and eventuallydeveloped a design which he called theéchappement naturel.

The échappement naturel 1, wasdevised to combine the advantages ofboth the lever and detent escapements.The then relatively new leverescapement had the advantage that itimpulsed the balance at each vibration,or twice per oscillation, but it achievedthis via an intermediary component, thelever. This was an entirely new concept.

Previous watch escapements such asthe verge, cylinder or duplex impulsedthe balance directly via the escape-wheel teeth. In the lever escapementimpulse was not delivered directly to thebalance by the escape wheel, and itrequired oil between the escape-wheelteeth and pallets. On the other hand, thevarious versions of the detentescapement impulsed the balancedirectly via the escape wheel and didnot require oil on the teeth. Bycombining the best features of boththese escapements, Breguet sought toproduce a superior double-impulseescapement that did not depend on oil.Breguet has been quoted asexclaiming, ‘Give me the perfect oil andI will give you the perfect watch!’ As thestability of 19th century oils was veryuncertain, Breguet was clearly on theright lines to dispense with oilaltogether. He favoured what he callednatural lift, which is simply another termfor impulse but with little sliding action,where the escape-wheel teeth engage

the balance directly. This, too, wassurely a good idea. The new detachedescapement functioned somewhat inthe manner of detent escapements butgave direct impulse in both directions ofthe balance.

Breguet used the échappementnaturel in his finest early series oftourbillons but eventually abandoned itin favour of the lever escapement.Although the design showed greatpromise, and fulfilled his requirementsof natural lift and non-dependence onoil, there were inherent faults which henever completely overcame, despitevarious changes in the design.

There were two main problems. Thefirst was that the twin escape wheelswere mounted on gears which linkedthem together. The escape wheelstherefore moved at the same time butrotated in opposite directions. This is anunfavourable arrangement because theinertia of the system is high and it wouldbe better for the wheels to movealternately anyway. The second

1. Breguet's échappement naturel. The left-hand escape wheeland pinion are driven by the train.The right-hand escape wheelis driven by the pair of toothed wheels from the left-hand wheel.Therefore both escape wheels move together but turn inopposite directions. A triangular locking jewel on the lever(shown in green) locks each wheel alternately. Unlocking iscontrolled by a ruby pin on the balance roller engaging a forkon the lever in a similar manner to that of a lever escapement.The balance is impulsed by one or other of the wing-like impulsepallets (dark blue). As shown, the balance is turning in aclockwise direction and the tooth of the right-hand escapewheel locked on the triangular pallet is about to be unlocked.The next tooth will impulse the balance. On the return vibrationof the balance, the left-hand escape wheel will deliver theimpulse in the anti-clockwise direction.

2. The Ulysse Nardin Dual-Direct escapement has much incommon with the échappement naturel. The inertia problemsexperienced by Breguet have been overcome by using newtechnology. A later version is more efficient and is in regularproduction.

After Daniels: ‘Escapements’

After Ulysse Nardin

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problem was caused by the necessityfor clearance between the gear teeth.As only one wheel is driven by thepower of the train, the other wheel ismerely a follower and the clearanceallows it to ‘flutter’ slightly. This meansthat it is not precisely positioned at alltimes, a condition which leads tovariable impulse, especially withchanges of position of the watch. Thisgives rise to small but unpredictableerrors of rate.

Breguet made various versions of theescapement to try and reduce theerrors. Some watches had a smallerdriven escape wheel, with as few asthree teeth, thus reducing the inertia ofthat wheel. It was not necessary forboth wheels to be the same, providingthat the ratio of the drive and number ofescape-wheel teeth remained correct.Other versions had vertical pins in thebands of the linked gears to serve asthe tips of escape wheels. This reducedthe inertia considerably. Anotherproblem, which Breguet apparently didnot realise at the time, was that therewas no draw on the locking pallet. Theeffect of this was that the lever carryingthe locking pallet was not positionedagainst the bankings with certaintyduring the supplementary arc of thebalance. The concept of draw was stillin its infancy.

Although the escapement showedmuch promise Breguet finallyabandoned it, rather than graduallyeliminate the remaining faults by yetmore development work. Heconcentrated on the lever escapementand made a number of valuablecontributions to its development. Onemay well imagine that he was reluctant

to discard the échappement naturel infavour of the lever escapement with itsdependency on oil. His various attemptsto retain oil on the pallets of his leverescapements, with drilled or slottedescape-wheel teeth, confirm that hewas well aware of the importance oflubrication but he also knew that itwould be better not to depend on it atall.

The Ulysse Nardin Dual-DirectEscapement 2, and its derivatives are arevival of the échappement naturelprinciple. Silicon, a new material as faras mechanical horology is concerned,has been introduced to combat theinertia problem. The escape wheels areplasma etched from this material, whichhas a lower specific gravity than thetraditional metals used to make escapewheels. The use of silicon in this way,plus the diamond-like coating of thesurfaces, is a very interesting hi-techdevelopment which we are likely to hearmore about in the future. Although theproblem of clearance between the gearteeth must remain, presumably that ofdraw on the lever has been addressed.Time will tell if the Dual-DirectEscapement has solved Breguet’sproblems with the échappementnaturel.

Thomas Mudge’s lever escapementwas developed steadily during the 19th

and 20th centuries until the optimumproportions were established. Work onother escapements gradually ceasedand the lever escapement became thestandard watch escapement. It iscapable of putting up an impressiveperformance, especially in the shortterm. However, in the long term theproblem of oil dependency remains.Better oils and greases have beendeveloped to lubricate the pallets duringthe sliding friction of impulse, butattempts to eliminate lubricationdependency fundamentally have notgenerally been pursued until recently.

George DanielsIn the 1970’s, George Daniels took

another look at Breguet’s échappementnaturel. He had unparalleled experienceof Breguet’s work having handled,examined and restored most of thesurviving watches. The definitive book,‘The Art of Breguet’ was written byGeorge Daniels in 1974 and by this timehe was already deeply involved with hisself-imposed task of reviving theflagging fortunes of the mechanicalwatch in the face of the quartz watchrevolution.

4. The first of a series of lever-escapement tourbillons with a one-second remontoiremade by Derek Pratt (HJ July 1991). The remontoire is a second escapement, co-axialwith the normal lever escapement. Its purpose is to rewind the small spiral springwhich provides the impulse to the balance. This spring is the sole connection betweenthe escape pinion and the escape wheel. The action of the remontoire is controlled by a3-lobed cam (Reuleaux Triangle) embraced by a fork. Later watches had ruby cams.

Photo: Toni Baggenstos.

3. In the Daniels Independent Double-Wheel Escapement, the contra-rotatingescape wheels are independently drivenby separate wheel trains. The escapewheels are alternately locked andunlocked by the lever with 3 pallet jewelsfor locking. The balance is impulseddirectly by the escape wheel teeth actingon the roller impulse pallets.

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I well remember seeing the first ofGeorge’s watches with his IndependentDouble-Wheel Escapement 3. The twoescape wheels are each driven byindependent trains. This eliminatedmost of the problems suffered by theéchappement naturel in one masterfulstroke. Draw on the locking pallets gavethe final security that was required for afirst class escapement that did notdepend on oil. The escape wheelsmove alternately, the inertia is low andthe lockings are secure. Theescapement is extremely lively in actionand very elegant, too. George went on

to make a number of watches using thisescapement, culminating in the brilliant‘Space Traveller’s Watch’.

I could immediately appreciate theconsiderable merit of this escapementbut my first thought was that it was apity that it could not be readily used in atourbillon because of the independenttrains driving the escape wheels. Istarted to think of ways around thisproblem and soon thought that two fixedfourth wheels, one with conventionalteeth, the other with internal teeth,would give the necessary contrarotation of the escape wheels. However,

it did not take long to realise that theproblem was much more complex thanthis. Two escape wheels pivoted in thecarriage would both have to movetogether and all that the two fixed fourthwheels achieved was to give therequired contra rotation. My originalsketch on a scrap of paper hassurvived, complete with my comment atthe time. I consigned the idea to the‘needs further thought’ file in my mindbut ‘took it’ out every so often for review.Many years passed but I simply couldnot just forget the idea because theescapement had really captured myimagination.

Meanwhile, George Daniels went onto develop the Co-Axial Escapement todispense with the complication of thesecond train. He immediately put thenew escapement into a tourbillonpocket watch where it performed verywell. Subsequently, he reduced thedimensions of the Co-Axial Escapementto wristwatch size and the rest, as the

5. The Pratt Independent Double-Wheel Escapement for use in a tourbillon watch. Onceagain, the sole link between the escape pinions and the escape wheels is the spiralimpulse spring. The escape pinions engage the two fixed 4th wheels. The outer wheelhas internal teeth and the inner wheel conventional teeth. Note that the teeth are onslightly different planes. The escape wheel units turn in opposite directions.

6. The tourbillon carriage with the bridge and balance removed. Note the black polishgiving the impression of a blued carriage! The insets show an extension of theremontoire-spring stud, fixed to the stop arm, resting on a fine radial pin in the band ofeach escape wheel. With no power applied to the watch, this arrangement is necessaryto retain the pre-set tension in the remontoire springs. In operation, the stud extensionoperates in the space between the radial pin and the adjacent wheel spoke but does notcontact either of them. Each escape wheel alternately serves the dual purpose ofimpulsing the balance directly and serving as the control wheel of the remontoirespring rewinding. As one escape wheel is delivering impulse to the balance, the otherremontoire is being rewound. Then the rôles are reversed. The remontoires provide anear-constant impulse to the balance, in each direction, and isolate the tourbilloncarriage from the inertia of starting and stopping the entire train of the watch at eachlocking and unlocking of the escapement.

8. The complete tourbillon carriage.

7. The lower pivot of the tourbilloncarriage is located in the central jewel.The 3rd wheel driving the carriage is justvisible adjacent to the jewel. As thecarriage rotates, the twin escape pinions(drawing left) rotate around their axes,driven by the fixed fourth wheels, but inopposite directions. The fourth wheelsand escape pinions have the same toothcounts but the internally-toothed wheelhas a larger module.

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saying goes, is history. But in this case itwas history in the making as the Co-Axial Escapement entered seriesproduction at Omega a decade ago.

Independent Double Wheelwith Single Train

Returning to the Double-WheelEscapement, I found that the solution tothe problem of both escape wheelsmoving at the same time arrived ratherunexpectedly during a session of lateralthinking. My brain suddenly gave outthe message ‘It is not strictly true thatthe escape wheels are obliged tomove at the same time; it is theescape pinions to which thisapplies.’ That was exactly theinformation I needed and the rest fellinto place very quickly. Having madeseveral tourbillons with remontoiresbetween the escape wheels and pinionsit was at last obvious in which directionthe solution lay.

In a remontoire mechanism, thewheel and pinion concerned are notrigidly connected to each other, as is thecase with a conventional train mobile.Generally the wheel runs on the arbor ofthe pinion and some kind of spring,often a spiral one, connects the twoparts. Additional parts provide a controlmechanism which defines when thespring is re-tensioned and by howmuch. The control mechanism is usuallyanother wheel which is concentric, or

co-axial, with the wheel which ispowered by the spring. In the case ofthe other remontoires that I have made4, this is the wheel with three teeth,fitted below the conventional escapewheel with fifteen teeth. The controlmechanism is a subsidiary escapement.I realised that the control wheel did nothave to be concentric with the escapewheel, provided that there was a directconnection. Such a connection isprovided by the carriage itself, so theoriginal problem now offered thesolution! If a remontoire mechanismcould be applied to each of the escapewheel-pinion units, both pinions wouldbe able to turn at the same time but onewould use this rotation to rewind itsremontoire spring while the otherpreviously wound spring delivered thestored energy to the balance via itsescape wheel 5-8. In this way, each of

the twin escape wheels serves a dualfunction. At any instant, one escapewheel is the impulse wheel and theother is the locking, or control, wheel.The carriage itself, via the pinions,provides the necessary connection.After delivery of an impulse, by one orthe other wheel, the roles reverse. I didthe opposite to George Daniels, whohad made the two escape wheels co-axial. I separated them, but for verydifferent reasons.

I drew a layout of the escapement at20X to explore the idea in depth andthen made some cardboard escapewheels and a lever. I call this design-aid‘CARD’, rather than ‘CAD’, which I donot use. The cardboard components arethen correctly positioned on the drawingboard with pins and the action of theparts can be readily investigated. I tookthis a stage further and animated the

9. An underdial view of the twin-barrelwatch. The mobiles of the Daniels-typepower reserve indication are beneath thecock near the left-hand winding wheel.The associated cone is visible on thefront-cover view of the movement. Thebimetallic blade of the thermometer isjust visible passing below the right-handwinding wheel.

10. The silver engine-turned dial is made from one piece of silver, with the exception ofthe seconds chapter ring which is a separate piece, held in place by three tiny screws.The linkage between the power-reserve cone and the indicator hand is a system ofsmall levers which convert a linear movement into a rotary one.

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previously static parts with elastic bandsto provide power and the resultingmodel is even capable of a few ticks,albeit with some hand assistance. Theidea looked feasible and it was time toget to work in metal. This was in 1996and the successors of Abraham Louis,Breguet SA, announced a competitionfor innovation in mechanical horology.The competition was to celebrate the250th anniversary of Breguet’s birth in1747. I had less than a year to make thewatch as my entry in the competition,although the rules did not call foranything to be made, just an innovativeconcept. However, I was impatient toactually make the watch now that thelong process of solving the basic designproblems had been completed. Thecompetition was exactly the stimulus

that I needed to start work in earnest. Ijust managed to complete the watch 9,

10, by the deadline for entries at the endof March 1997. I did not win thecompetition but the watch now existedand worked. I felt that at least AbrahamLouis Breguet would probably be quiteintrigued by my solution to the problemsthat he had experienced with theéchappement naturel in a tourbillon.

PostscriptI continued to think about the Double-

Wheel Escapement after completing thetourbillon, but for a wristwatch, withouttourbillon. I made an initial design studyto investigate the layout possibilities ofthe keyless work and other details butdidn't progress much further. Soon after,I was asked to make a prototype

wristwatch with a pivoted-detentescapement. This ran reasonably wellbut I felt that it would be very difficultindeed to make the watch absolutelyreliable under all circumstances ofnormal wear, without adding excessivecomplications to an otherwise very pureescapement.

Meanwhile, other good friends inEngland were thinking about detentescapements for wristwatches (see ValCarr: HJ September 2004 p318-21‘Developing a Wristwatch with aChronometer Escapement’) and wediscussed the pros and cons at length.In particular, the team at CharlesFrodsham had several spring-detentprototype wristwatches running verywell. However, the watches didsometimes fail, despite well-madecountermeasures, and we eventuallycame to the conclusion that a single-impulse escapement was never goingto perform with the absolute reliabilitythat we were seeking.

In May 2004 we spent a long daytogether at the Charles Frodshamworkshops in Sussex talking around theunfortunate truth. At this point, theinevitable question arose; ‘What can wedo now?’ I mentioned my thoughts onthe Daniels Double-WheelEscapement, indeed I had the tourbillonwith me, and a new chapter ofhorological history began that eveningas the ideas started to flow again.

Within nine months a prototypewristwatch was running 11, andshowing great promise. Since then agreat deal of careful development andpre-production work has beencompleted and ‘Independently Driven; aWork in Progress’, together with threepre-production movements, waspresented at the BHI 150th AnniversarySeminars by Charles Frodsham & Co.in June 2008.

Derek Pratt FBHI

11. Charles Frodsham’s wristwatch version of the double-wheel escapement. To give anidea of the scale, the balance diameter is almost 14 mm.Note the sophisticated attention to detail in the design of the timing weights on the free-sprung balance, the Frodsham balance shock-proof settings and the bankings (shapedscrew heads visible below the balance). Also note the great rigidity of the balance andescapement bridges. The frequency is 21,600 vph (3 Hz).