Automatic Movements : 2824-2 / SW200 vs 2892-2 / SW300

I received an e-mail asking me about a movement in the Oris Aquis Date. While I am no professional to talk about the watches' movements (leave that to watchsmiths like my father), I have read a fair bit of information over the years; and one of my favourite explanation was from http://www.chronometrie.com which I would reproduce below later with credit back to the writer.

Essentially, the Aquis Date utilises the Sellita SW200 automatic movement, which in itself was a clone of ETA's 2824-2 after the latter's patent ran its course. Essentially a workhorse of the Swiss watch industry, this movement is built tough, robust, thick (well, relative to its elder brother ie 2892-2 (ETA)/SW300 (Sellita) which are 1 mm thinner), and inexpensive. Dependable as heck, it was no coincidence that the movement is so widely-used in various Swiss watches and especially so in Breitling's range. The 2824-2/SW200 has 25 jewels.

The ETA 2892-2/Sellita SW300 is thinner by 1 mm, more refined, has better built-in shock absorb-ability (which could be due to its thinner self thereby requiring the extra protection), less wear-and-tear during the long run due to is larger rotor and claimed (and counter-claimed by lovers of 2824-2/SW200) to have better time-keeping. The 2892-2 has 21 jewels only, while SW300 has 25 jewels. Of course, more jewels would be welcomed but in the horology world, ETA is still the bigger entity compared to Sellita.

Watches with GMT would utilise a variation of the above ie 2893-2, which accommodates the extra time module.

For a more in-depth study, please read ETA 2892 part 1, ETA 2892 part 2 and ETA 2824, which were re-produced as per the following :


The Little Engine that Could
An indepth look at the ETA 2892  
 
Hans asked me a while ago to do a write up on the ETA 2892. Both because of its enormous popularity and also the fact that it is deemed accurate and reliable enough to be used as a base movement for many high-end manufacturers complications. 
There’s not much I can add to Walt Odets’ history and evolution of the movement itself, except to say that most changes and updates were done in order to improve the efficiency of the automatic winding. 
 
The first problem arose because originally the basic movement beat at a leisurely 18,000 beats per hour (BPH) and had a fairly large diameter balance wheel. When ETA upgraded the movement by increasing the beat to 28,800 BPH, this required a much stronger mainspring than what was used previously. This required upgrading the automatic unit by improving its winding efficiency in order to deal with the extra resistance due to the stronger mainspring. 
 
No sooner had the above problem been adequately dealt with, when ETA gave themselves more winding efficiency headaches by reducing the diameter of the movement from 28mm to 25.6mm so that it could be used in a wider range of cases. Hence the change in model number from 2890 to 2892. Thickness remained unchanged, i.e. 3.6mm for both models. This had the effect of reducing both the diameter and mass of the oscillating weight. A problem that was finally put to rest with modifications that resulted in the latest model, 2892/A2. 
 
For the more technically minded, the final modifications to the automatic winding was to reduce the chamfer around the circumference of the oscillating weight – thereby increasing its mass. And to switch the stud and the jewel which supported the intermediate reduction wheel. This wheel, which drives the ratchet driving wheel, originally had a stud, but now has a jewel. The stud has now replaced the jewel in the upper part of the automatic winding bridge. This resulted in less winding friction due to this wheels much greater stability. Omega (and Girard Perregaux) have increased the winding efficiency further by reducing the diameter of the ball bearing support. 
 
I have ‘dissected’ a Bulgari labeled Girard Perregaux modified 2892 for you. So let’s take a closer look at it starting with its source of power, the mainspring. While not being very high, this is quite a strong mainspring and provides the movement with a more than adequate supply of torque. The barrel arbor has a small diameter relative to the size of the barrel. This is in keeping with most modern movements that use fairly long mainsprings. This results in the mainspring taking up about 75% of the available space, as opposed to older movements whose mainsprings only utilized about 50% of it.
 



Picture 2 shows the barrel complete. Like the rest of the watch train, it utilizes micro gear toothing. Also known as ETA style teeth. This particular shape, invented by ETA, was chosen for both the wheels and pinion leaves, in order to improve the efficiency of energy transmission by keeping friction to a minimum. Most modern movements, regardless of the factory producing them, have switched over to these style teeth. I think it was Curtis, after much research, who gave us a pretty accurate description of these teeth quite a while back.
 


What amazes me as a watchmaker, is how well these teeth work. One can easily check this out by assembling the going train of any high grade watch that has the epicycloidal teeth. Without oiling any of the pivots, give the great wheel a push with a thin oiler. Now do the same with an ETA 2892, or even a Rolex 3135 for that matter. The wheels of the latter turn much more freely. 
 
Picture 3 shows the complete train and the escapement. Nothing fancy there, just overall good basic engineering. Note that the wheels are made of glucydur and the pinion leaves are made of steel. Dissimilar metals rolling together produce considerably less friction than if they were made of identical material. All the wheels in quartz watches, high grade ones included, are made of brass. Due to the fact that there is much less torque in a quartz movement, there is no need for the greater strength of the glucydur wheels.
 



The main plate, like almost all of the rest of the bridges and plates, is made of stamped brass. Most manufacturers rhodium plate these, both for aesthetic reasons and corrosion resistance.
 


Here is the going train and barrel sans bridges. The brass colored wheel on the barrel is the ratchet wheel.
 


The inner workings of the wheels that fit under the barrel bridge. The ones on the left facilitate hand winding, while the one on the right, the ratchet driving wheel, is the final working wheel of the automatic unit. The spring, together with the smaller diameter steel wheel, serves a double function. The part engaged with the brass colored wheel functions as a click. While the part resting on the steel wheel, functions like a clutch. Forcing the wheel to be engaged during hand winding, and allowing it slip and move out of the way when the auto winding is engaged. The football (rugby for our European readers) shaped post that it turns on determines its free play in both directions.
 


Picture 7 shows the barrel bridge fully assembled and ready to be installed.
 

Here is the complete movement sans the balance wheel.
 


Picture 9 shows the balance wheel installed. The 9mm diameter balance is a good compromise between weight and size. Both the ETA 7750 and Rolex 3135 have approximately 10mm balances. In ETA’s cheaper versions the balance is made of nickel. The ETA-Chron system makes centering the hairspring and adjusting the gap between the regulator pins very quick and easy. Unfortunately it also makes replacing the balance wheel complete quite a bit more difficult. The screw for fine regulation of the timekeeping, should not be used for more than a 5 second adjustment. Ideally it should be centered, as shown.
 


The dial side of the movement with stem, setting and winding system installed.
 


The complete dial side ready to be fitted with a dial. The large brass wheel at the 11 O’ clock position is the calendar driving wheel. The brass tooth peeking out from under the steel wheel cover, is the tooth that actually flips the date. This ingeniously simple design has been copied by many other manufacturers due to its simplicity, reliability and the fact that it gives a virtually instantaneous date change without needing extra parts. It’s also foolproof, such that one can change the time whether it’s engaged or not without damaging anything.
 


The automatic winding train. The wheel second from the right is the reversing wheel. This wheel, together with the middle wheel, facilitates winding in both directions. The first wheel on the left is the intermediate reduction wheel. One can clearly see the jewel that replaced the stud. It sits on the small stud fitted at the top 12 O’ clock position of the automatic winding bridge.
 


Here is the auto winding unit complete, ready to be installed in the movement. With weight upside down one can clearly see the heavy weight riveted to its circumference.
 


Voila!! The complete movement ready to be installed in the watch case.
 


So what exactly is it that makes this movement so special? Or to rephrase the question, how come this movement is so accurate and reliable? Beats me if I know!! To be perfectly honest, I think that it is just a great design with compromises that have been intelligently chosen and superbly executed in its best incarnation. It incorporates all the latest knowledge and advances in both materials and movement design. Its generous supply of available torque means that it will not be easily stopped, even when powering extra complications. 
If I was given carte blanche, what would I do to improve this movement? 
 
Firstly, I would make all the bridges out of invar. This wouldn’t do anything for its accuracy, and probably as much for its reliability. But as a watchmaker it distresses me to see high end movements made out of brass. Brass is just so…… cheap. It also has a very poor coefficiency of expansion. Invar has a virtually zero coefficiency of expansion through a very wide temperature range. It’s also considerably stronger than brass. Being stainless obviously obviates the need to plate it too. How come Hamilton, Elgin et al produced zillions of inexpensive movements made of invar or similar alloys, but Rolex, JLC, Patek Phillippe etc make their very expensive movements out of cheap brass?? 
 
Secondly, I would do a complete redesign of the automatic winding unit to improve its efficiency even further. I would eliminate the reversing wheel and incorporate a JLC style switching rocker. And I would further reduce the diameter of the ball bearing oscillating weight support. That’s one of the reasons for the Rolex’s winding efficiency, the weight spins on a tiny diameter post. Unfortunately they’ve taken winding efficiency to the extreme. The net result is that said tiny diameter post doesn’t offer enough support to the weight. This results in the weight scraping up against the movement bridges, even with mild shocks. 
So how does it compare to the competition? There are some movements that match it in terms of accuracy and reliability, but in my humble opinion, none exceed it. The Rolex 3035 and 3135 match it toe to toe. But they are a lot thicker and considerably more expensive too. The PPs, while being very pretty to look at, do not match it for accuracy and are more delicate as far as reliability is concerned. Of course they’re also slightly thinner, so that does put them at a disadvantage. The JLC 889/2 does match it for accuracy, but is also too delicate to give it any competition in the reliability department. The main reason for the latter is its very weak mainspring. The whole design, while being well thought out and superbly executed, relies too much on everything being just perfect. It is just thrown out of wack too easily, when even minor things go out of adjustment. I don’t have too much experience on the Blancpain/Piguet movements. But from the few that have crossed my bench, they don’t seem to deliver the same accuracy that the 2892 has no trouble delivering. Let me know if I’ve left any of your favorite movements out, and I’ll gladly comment on them.

 ETA 2824 - Another Little Engine that Could
text and images by A Watchmaker
 
In response to an article on the ETA 2892 written by a befriended watchmaker, many people requested that he took a closer look at that movement's "smaller brother", the ETA 2824.  

Looking through Heinz Hampel’s excellent book, ‘Automatic Wristwatches from Switzerland’, it appears to me as if the ETA 2824 is also an Eterna derived caliber. Although not identical, it definitely seems that the Eterna Caliber 1429/1439 U was used as the base design for the ETA. I’m no expert in movement design, or movement history, so perhaps one of our technically minded history buffs can make further enquiries in that regard. Like its Eterna cousin, the Caliber 1466U, it too started out at a leisurely 18,000 BPH. It does predate the latter by a couple of years though, being introduced in 1961 according to Hampel.

Click here for the corresponding view of the ETA 2892

Eterna Caliber 1429U

image from Hampel's 'Automatic Wristwatches from Switzerland'

Like all ETA products it too has undergone continuous refinements to bring us the work horse that we know today. If one were to check through old technical literature, one would see that this caliber has also had many reincarnations in slightly different guises and beats. All the way from 18,000 BPH, right up to the super-fast 36,000 BPH. Often times, many of the parts being completely interchangeable.

Dimensions and Differences 

Dimensions are very similar to the 2892. Casing diameter is identical, 25.6mm, but the overall height is slightly more, 4.6mm versus 3.6mm. That doesn’t sound like much, only 1mm thicker. Still, considering the small dimensions that we’re dealing with, 4.6mm is almost 28% thicker than 3.6mm.

As one can see when comparing pictures of the two movements, they have many similarities. I’m not going to point out every single difference between them, but the main differences are;

a)     more generously proportioned wheels

b)     larger diameter balance wheel

c)      smaller diameter ball bearing race support

d)     crown and ratchet wheel fit on top of the barrel bridge

e)     two reversing wheels in the automatic winding system, and lastly

f)        the automatic unit fits on top of the movement.

 

Why Both are so Beloved by the Watch Companies

Click on image to view a larger version

Click here for the corresponding view of the ETA 2892

Generally, integrating the automatic unit into the movement and fitting the crown and ratchet wheel underneath the barrel bridge, results in a slightly thinner movement. Both of them have a very similar layout of the drive train, namely, the great wheel, third wheel and second wheel (still erroneously referred to as the fourth wheel by many) are almost in a straight line, with the escape wheel slightly offset to the side. Both of them supply the drive to the dial train via the third wheel. Most significantly, both lend themselves well to the attachment of modules and extra complications and both have plenty of torque to spare in order to drive said complications without drastically affecting either the amplitude or the timing.

 Click on image to view a larger version

Click here for the corresponding view of the ETA 2892

In fact, if the attachment of any module reduces the balance amplitude by more than 15 to 20 degrees, then that module is obviously in need of a service. This should be a cause of concern for most customers, because the majority of watchmakers do not service these modules. They are removed, the basic movement serviced and then reattached. Most major brands don’t bother servicing them either, they just fit a brand new movement and module and return the old one to Switzerland for refurbishing, and the service charge usually reflects this.

Why? Because most of these modules, be they chrono or perpetual calendar modules, are very complicated and require qualified technicians to service and adjust them. Attachment of a module in dire need of a service, or one serviced incorrectly, can pull the amplitude down by as much as 200 degrees. Such a watch, regardless of how stellar the performance of the basic movement is, will not keep good time on the customer’s wrist.

Accuracy

So, the million dollar question that most aficionados have been waiting for – how does the ETA 2824/2 compare to the ETA 2892-A2? Or more specifically, is it as accurate and as reliable as the latter?

Keep in mind that the following is my own personal opinion, and in that area I am influenced only by what I see at the bench and my experience gained from working on these and many hundreds of other movements.

I don’t see any difference in accuracy between the two, provided that they are both fitted with the highest – chronometer – grade parts, carefully lubricated and adjusted to the best accuracy possible. Of course, very few fall into that category, so it’s no wonder that the 2824 has gotten a bad rap as the 2892’s poor cousin.

Reliability

As far as reliability is concerned, they seem to be on a par, but I do think that the 2892 has the edge when it comes to long-term wear, or lack thereof. The larger support for the ball bearing races means better support and hence better shock protection for the oscillating weight. Also, because this has been ETA’s inexpensive work horse for so long, and only recently started supplying it with the highest quality parts, ETA haven’t invested the same amount of effort into refining this movement, as they have in the 2892. This is best seen in the automatic unit which doesn’t appear to have undergone much change since its days as an Eterna incarnation. As a result, it seems that parts in that unit seem to wear out faster than the rest of the movement.

Having said that though, there really shouldn’t be any significant difference in wear between the two if both are serviced at regular intervals. Which should be every three to five years if the watch is worn every day, depending on how hard one is on one’s watches.

Personally, I am amazed that ETA can produce such a thin movement as the 2892-A2 and not only make it as sturdy and as reliable as their thicker movements, but as I mentioned earlier if there is a more accurate or reliable movement than this, I haven’t seen it.

Tying it All Together from My Soapbox

While I’m on my soap box there are a few other related issues which I feel need to be addressed.

First of all, the basic issue of what makes an accurate movement? Repeating what I said before, I believe that any good movement is an excellent execution of a design whose compromises, while as few as possible, have been intelligently chosen. Making any one area outstanding, while neglecting others will result in a flawed movement.

An example of the above? I think that the Patek Philippe Caliber 315 is a perfect example. In its incarnation as Caliber 310 they had a movement that was very thin, had a large central oscillating weight, was very accurate and reliable, but had undue wear in its automatic winding system. Instead of just refining and fixing up what was wrong, namely choosing better reduction ratios etc better suited to the higher torque 28,800 beat movement, they completely redesigned it and simultaneously reduced the stress on it by reducing the beat to 21,600.  So now they have a movement that is outstanding in its efficiency of the automatic winding, and only mediocre as far as accuracy is concerned. Mediocre for PP that is.

In my experience, the PP Cal. 315 is not as accurate as its older cousin, the PP Cal. 240 and significantly less accurate than its predecessor, the PP Cal. 310. Don’t get me wrong, it’s still a great movement, and is capable of reasonably good timing, but in their quest to improve one area – automatic winding wear and efficiency – they had significant losses in another area – the important area of accuracy. In my opinion, the change in accuracy is due mostly to the reduced beat and the gyromax balance, as the basic going train is virtually unchanged. Specifically, the great wheel, third wheel and pallet fork are interchangeable between the two. So, all in all, in my book, the compromises for this movement could have been more intelligently chosen.

A second example of the above is Rolex’s insistence on sticking with the archaic oscillating axel for the sake of winding efficiency, instead of switching over to ball bearing races like virtually everyone else. Including them for their new Cal. 4130 chrono movement.  The result is movements that are very accurate, but suffer undue wear due to the oscillating weight scraping up against the movement bridges every time the watch suffers a slight shock. And not to mention many broken axels, and, although less common, broken axel jewels for the same reason.

Which brings me back to the issue of accuracy. What exactly is my (and most watchmakers) definition of an accurate movement. Easy, one that is consistently easy to get good amplitude and good timing from, and doesn’t have undue loss of balance amplitude from the horizontal to the vertical positions. COSC quality timing can be achieved by most good quality movements, but ones that are inherently accurate don’t require any special skills or hours of delicate tweaking to achieve that goal. If one achieves outstanding timing from a movement after many hours of tweaking, to me that’s not a reflection of how accurate the movement is, but rather a reflection of how talented the adjuster is. As has been pointed out before, almost any movement can achieve outstanding timing if enough time, effort and talent are spent on it by one who is an expert in that area. 

 

On the other hand, if most watchmakers can achieve outstanding timing with a minimum of time and adjustments, that’s a reflection of the inherent accuracy of the movement. Of course there’ll be those that disagree with me. This is just the way that I see these things.

 
The Proud, the Few, the Accurate

So which movements meet my criteria? This short list of outstanding movements should all easily achieve a daily consistency of five seconds or better on the wrist. Those people wanting better accuracy than that, will be much happier with a thermo or radio controlled quartz watch.

Of those currently in production, I’d list the ETA 2892-A2, ETA 2824/2, ETA 7750, JLC 889/2 (and its variations by other brands), JLC 960, all of the current Rolex calibers, Longines 990 (Lemania 8815), PP 215, PP 240, Zenith 400. This is a very small list, I know, mainly because there are many fine movements with which I have very little, or no experience at all. L.U.C. Parmigiani etc.

Some movements that I’ve found delivered excellent timing, but I’m reluctant to put them into the above category because I’ve only serviced/timed one or two of them. FP 1180, FP 1150, Lange 901.0, Omega 2500, Zenith 670, GP 3100.

ETA 2892 Flavors

Quite a few people were curious about the fit and finish of the various 2892’s currently on the market. That’s a really difficult question to answer, as some types of finishes are more attractive than others. Also, some give the appearance of a better finish, when in reality it’s just a finer decoration finished to the same degree. For example, fine perlage versus heavy stripes.

My experience has been that the ones that have the nicest quality finish are Breitling, Cartier GP/Bulgari 220, Frank Muller 2800 , IWC’s 375XX and the Ulysse Nardin. The Omega 1120 is one small step above the others. Why do I put it slightly ahead? Because it’s the only one that is as nicely finished on the dial side as it is on the working side.   

Omega Caliber 1120

Click on image to view a larger version

All of the above tend to be very well adjusted in terms of fit and timing, excepting the Cartier. Unless, of course, the watch was in a package that was used for football practice by UPS/FEDEX or the USPS on route to your wrist. A small investment in time and effort could easily bring the Cartier up to par. I should also point out that only the Frank Muller and IWC appear to completely lubricated by hand, save for the barrel and mainspring. The others appear as if they have gone through bulk lubrication. Not necessarily a bad thing, but certainly quicker and cheaper.

Omega’s Co-axial

  

Finally, just a few words about Omega’s co-axial escapement. I don’t have enough words of praise for Omega’s sheer courage, guts and fortitude in taking on Daniels co-axial escapement. This is a project that required not only enormous courage in venturing into the unknown – is there anybody out there that can say with a straight face and 100% honesty that they really understand this design, besides Dr. Daniels himself? – but also a significant investment on their part in order to make and adjust parts to tolerances of unbelievable precision. Yes, there were teething problems in the first batch. No whining and crying on their part. Back to the drawing board, ever tighter tolerances and even greater precision in manufacturing and voila, it finally seems to be delivering what was promised all along. Greater long-term stability in amplitude and timing.

Yes, I know that Omega boasted that now service intervals can be dragged out to ten years. I don’t see how, as all the other parts are still subjected to the same stress and wear as a movement without the co-axial escapement. For example, the barrel and mainspring, the automatic winding unit, the great wheel and third wheel and the dial train too.

From what I’ve seen, it definitely seems to deliver long term accuracy and stability. As far as long term wear and tear are concerned, it’s still too soon to tell. But I’m going to put my money where my mouth is, and hopefully buy one for myself in the not too distant future. I think it’s that good. And no, I neither work for Omega nor have shares in Swatch or any of their subsidiaries.