Chronographs - Vertical And Horizontal Coupling

By request here is some information on vertical clutch chronograph watches. But before we talk about vertical clutch mechanisms, we should cover the basics of the more common horizontally coupled chronograph.

The first thing we should look at it the design of the teeth on the wheels (gears). Now here is what typical wheels look like in the wheel train of a watch. So here you see the teeth on these are multi-radius teeth, with rounded tips, and they are designed with efficiency, low running friction, and minimal wear in mind:



Here is a photo of an Omega Cal. 861:



Now I just want to point out that the part with the “A” on it will swing in and out in the direction of the red arrow to engage and disengage the chronograph.

Now here is a closer shot of the teeth, with the chronograph switched on, so that part A has swung in and the teeth are meshing to run the chronograph:



Now the shape of the teeth here are quite different than those I showed above, and they are very sharp and pointed. The reason for this is that the wheel on the left in that photo is always turning, and when the chronograph is switched, that wheel moves in towards the wheel on the right with much smaller teeth. If the teeth were not pointed, there is a much greater chance that the teeth will not mesh correctly, and the very tips of the teeth will hit each other, causing the chronograph to not engage or the hand to jump forwards or backwards. Even with these sharp teeth the hand can jump forward when you press the start button sometimes.

In addition, these teeth are not as efficient as those designed for pure power transmission as shown above, and these teeth can wear more both from just running and also from the teeth hitting each other when they are trying to couple and start the chronograph.

Another horizontally coupled chronograph is the very common ETA 7750. However is is a bit different design than the Cal. 861 is. In this style there is a very small gear called the oscillating pinion that is used to turn the chronograph on and off. Here is a video that shows the oscillating pinion being engaged and disengaged:


It also has teeth that are not really optimized for transmission of power, but to provide minimal interference when the chronograph started.

So how is a vertical clutch different? Well as the name suggests the action to engage and disengage the chronograph is vertical, so along the axis of the shaft of the chronograph runner. Here is a photo of an Omega Cal. 3301 that serviced a while back - I have added some information to explain a bit how this works:



So A is the column wheel, located under the cap that I have placed the letter on. The column wheel is just a type of switch, and both this and cam operated chronographs perform the same function, and are not related to the vertical clutch at all. Both perform the function of switching well, but the knock against the cam operated type is that the pushers can be more difficult to press, where the vertical clutch offers a nice easy pusher feel. Collectors seem to value the column wheel a lot, but the cam operated style is really just fine in terms of operation. I think because it cheaper to make, people see the cam as less effective, but really it isn’t.

Part B is the chronograph runner, and this is the part that carries the central seconds hand for the chronograph function – a long post goes through the middle of this assembly. In a horizontally coupled chronograph, this wheel is separate from the timekeeping train of the watch, and is only activated when the chronograph is switched on. In a vertical clutch system, this wheel serves 2 purposes. It is both a train wheel and a chronograph wheel, so in fact a portion of this wheel assembly runs all the time when the watch is running.

Note - please excuse the vibrant blue Moebius 9504 grease in the photo above. This watch is known for having some issues with lubrication, and Omega calls for a pile of lubrication in some areas such as the crown wheel shown here. I did clean up the excess grease, but this watch actually came in with the crown wheel seized to it's core, and the winding pinion with several teeth sheared off, so getting lots of grease in there is important.

Here is a shot of 2 runners from the Seiko 6139 A and B variants, and you can see this is a complex assembly:



The large diameter gear is actually part of the wheel train of the watch, and must run all the time just for the watch to function. The chronograph portion runs through the center of this wheel, and when the chronograph is off, it stays stationary, and the large gear is the only thing that turns. So the two portions of this part have some friction between them when the watch is running, and the chronograph is turned off. When the chronograph is switched on, the whole unit turns, so although there is some added load from moving other parts in the chronograph, the friction between the two parts of this runner (wheel and chronograph parts) is less than when the chronograph is turned off.

Now back to the Cal. 3301 photo, and parts C and D are the parts that swing in and out to engage/disengage the clutch, which is a spring loaded disk. When they swing in, they press on the underside of the flat disk like part on the runner, and this lifts the disk and disengages the chronograph portion of the runner from the train wheel, so the gear portion keeps turning, and the chronograph hand stops. When they swing out, they let the disk go back down, and the whole assembly turns.

The advantages to the vertical clutch, at least in theory, are many. For one it does not cause a "jump" of the chronograph seconds hand when the chronograph is started that you can have on a horizontally coupled system due to the teeth meshing. Second, because there are no sharp teeth to engage/disengage the chronograph, this one can run all the time with no harm done or excess wear. Lastly, this design actually causes less drag and amplitude drop when the chronograph is running than a horizontally coupled design does.

The biggest draw back is the chronograph runner assembly - these typically can't really be "serviced" at all, and they should not even be put through the cleaning machine according to most brands as this will wash away the factory applied lubrication. The lubrication between the gear that turns all the time and the chronograph runner post is critical, and it can’t really be renewed in the field, so if this part is seized, it has to be replaced. When these two parts seize together, the watch will run with the chronograph on, as the whole unit turns, but when the chronograph is switched off, the watch will stop as the large gear will no longer turn. I had mentioned the Seiko 6139 previously, and I will say that new old stock chronograph runners are sometimes quite hard to find for these models. One thing you should always check if you are considering a purchase is if the watch runs with the chronograph switched off on a 6139. If it runs with the chronograph on, but stops when it's turned off, the runner has seized and it will be difficult if not impossible to get it running again without a new runner.

Now about leaving your chronograph running all the time...personally for most watches where parts are available, I really would not have any problems letting the chronograph run. So on an Omega 861/1861, or a 7750 based watch, the parts that would need replacing from excess wear are readily available and not expensive. So if you want to let it run all the time, then in my personal view, go ahead. For a watch where parts are less easy to find, such as a Cal. 321, I would not recommend it. Again you want to preserve the parts in that movement as much as possible.

Now many people have asked on various forums “Does leaving my chronograph running all the time change the power reserve?” The answer to that is no it doesn’t. Power reserve is a calculated value based on the number of turns the barrel makes and the gearing in the watch, and since none of those change when the chronograph is switched on, the reserve is not changed. However with a horizontally coupled chronograph in particular, the load on the movement increases when the chronograph is running. So the watch will likely stop sooner with the chronograph on, simply because the torque supplied by the mainspring can’t overcome this additional load. If you leave a watch running with the chronograph on and let it stop, switch the chronograph off and the watch will probably continue to run for several hours.

Hope this helps, and if you have any questions, please let me know.

Cheers, Al

Finally, chronograph talk!

I didn't know about the vertical clutch not being able to be relubed. Makes complete sense of course once you spell it out for me....

Awesome piece Al!

Al, what are your thoughts on leaving the chronograph running on the two Seiko vertical clutch movements? I've read on some of the Japanese watch forums that it is actually recommended to leave them running and use the chrono hand as more-or-less of a seconds hand. They go on to say that there is less friction and wear to the movement with the chrono running.

Is this true?
gatorcpa

Yes, to a point. As I explained above, when the chronograph is turned off, the two parts of the chronograph runner have friction between them, since the large wheel must turn for the movement to run, and the chronograph hand does not move. Running the chronograph eliminates the friction between those 2 parts, but adds other loads such as the friction between the 2 ends of the shaft that the chronograph hand is attached to (one end in a jewel, the other in the tube of the center wheel). Also, there is the added load of the minute counter ticking over. Not sure I would say off or on has the most load - I would have to have the watch on the timing machine and measure the balance amplitude in both cases to confirm if one has more load (and lower balance amplitude) than the other.

But one thing you need to do with these is to run them with the chronograph off at least every so often. This will help prevent the chronograph runner parts from seizing together.

Cheers, Al

I can't speak for the Breitling, but the Omega 9300 tech guide does not indicate that the runner can't be washed, and it shows lubrication instructions for the runner, so it looks like that one can be serviced in the field.

Cheers, Al

The chronograph runner has the spring loaded vertical clutch integrated into it, however the parts that activate the clutch are not. If the runner is defective, it would be replaced. It can't be disassembled to have individual parts changed. This is true for any of these though, to the best of my knowledge.

Hi Ricardo and welcome to the forum. We hope to see you here often.

Since we are an English language forum, I have taken the liberty of having your question translated for the benefit of the majority of our members who don't speak Portugese. I used Bing traslator software. It seems to have given a decent result.


Hope this helps,
gatorcpa