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The "center wheel"

RobBrandywine
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RobBrandywine Member

RobBrandywine

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I was reading this interesting site today:

Mechanical Marvels: Understand the wheel train

It says:

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Center, or Second Wheel – which turns once per hour. Its pinion is turned by the teeth on the Mainspring Barrel. Its arbor projects through a hole in the face and drives, via a friction coupling, the Cannon Pinion, which carries the Minute Hand. It also drives the pinion of the Third Wheel. In wristwatches with center seconds, that is with the Second Hand pivoted coaxially with the Minute and Hour Hands, this wheel is positioned off-center to allow the Fourth Wheel to be placed at the center of the Movement. In this arrangement, the wheel is called the Second Wheel, because it is still the Second Wheel on the train but no longer at the center of the Movement.

Does this mean that, on watches with the second hand in the center of the watch, that it is the shaft of the fourth wheel that is projecting through the cannon pinion -- and not the 2nd wheel shaft?

Edited by RobBrandywine
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Zandr Member

Zandr

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Yes, it's the fourth wheel if you have center-seconds. It's not something I've come across in watchmaking circles, but this is a beautiful explanation of the mechanics of a modern wristwatch, including calendar and automatic works:

https://ciechanow.ski/mechanical-watch/

All his explainers are really excellent, with great animations you can manipulate to see what's really going on.

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Kalanag Super WRT Addict

Kalanag

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This animated tutorial is based on the ETA 2824.

To avoid confusion it should be mentioned, that between the barrel (first wheel) and the offset center wheel (second wheel) this movement has an so called intermediate wheel.

Edited by Kalanag
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Zandr Member

Zandr

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Well, after Kalanag's post, now I'm confused. In both the tutorial and the ETA 2824 tech sheet, there's a barrel, three wheels in the train, and an escape wheel. The second hand is attached to the fourth wheel. Center seconds arranges to have the fourth wheel in the center of the watch. I don't know what you're referring to as an intermediate wheel in either.

The ST36 (ETA 6497 clone) on my bench has the same wheels, though the fourth wheel is off center, so you get "small-seconds". In this case the canon pinion is attached to the second/center wheel.

What am I missing here?

image.png

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RobBrandywine Member

RobBrandywine

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Thanks for confirming, Zandr.  So many videos that I've been confused by make sense now.

Kalanag - when you say "this animated video".  What video are you referring to?

I'm being a little lazy by not studying a bit more, but how does the minute and hour information get to the cannon pinion?  Does it come in from the dial side? The video I'm currently watching makes it look like the gear on the cannon pinnion is being turned by the "minute wheel".

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Jon Super WRT Addict

Jon

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I find it confusing as well, that's why I don't go with what the tech sheet for 2824 says because they have named the wheels differently. Bloody Swiss!! ; the intermediate wheel is the second wheel. In the 2824 tech sheet, they call the fourth wheel a 'seconds wheel' which is very confusing!  Let's keep it simple, from the barrel, which is technically the first wheel, which drives the second wheel (intermediate wheel) which drives the third wheel, which drives the fourth wheel (seconds wheel) which drives the escape wheel to the escapement. On a 2824 there is no centre wheel, as it is an indirectly driven minute movement. There is a fixed pipe in the centre that the fourth wheel (seconds wheel) passes through. The cannon pinion driving wheel that sits on the fixed centre pipe is driven by the third wheel pinion. All modern ETA movements have this arrangement, rather than the traditional hollow centre wheel (second wheel) in the centre with a fourth wheel passing through it that holds the second-hand, or a sub-dial fourth wheel.

Edited by Jon
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Zandr Member

Zandr

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14 minutes ago, RobBrandywine said:

The video I'm currently watching makes it look like the gear on the cannon pinnion is being turned by the "minute wheel".

This is the case on what Jon calls 'indirectly driven minute movements". Let's use that for consistency. So in these, as Jon says, the third wheel drives another wheel that turns the cannon pinion.

3 minutes ago, Jon said:

All modern ETA movements have this arrangement, rather than the traditional hollow centre wheel (second wheel) in the centre with a fourth wheel passing through it that holds the second-hand, or a sub-dial fourth wheel.

With this I think we're declaring the 6497 as non-Modern. 😄 By the tech sheet it looks like the cannon pinion is directly seated on the center/second wheel. Same with the ST36 on my bench right now. (There are other differences between the ST36 and the 6497, so I'm being cautious here.)

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RobBrandywine Member

RobBrandywine

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I'm watching an excellent disassembly of the NH36 by Macro Time:

Macro Time

at 12:12, he begins removing the wheels.  It looks to me like the shaft of the 4th wheel (which turns once per minute and drives the seconds hand, right?) goes thru the center of the center wheel behind it with a small gear (pinion?) sandwiched between them.  Is that the way most center seconds watches are set up (but from the above comments, NOT the ETA 2824?

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Kalanag Super WRT Addict

Kalanag

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2 hours ago, Zandr said:

Well, after Kalanag's post, now I'm confused. In both the tutorial and the ETA 2824 tech sheet, there's a barrel, three wheels in the train, and an escape wheel. The second hand is attached to the fourth wheel. Center seconds arranges to have the fourth wheel in the center of the watch. I don't know what you're referring to as an intermediate wheel in either.

You are absolutely right! Sorry for my confusing comment!

ETA calls this wheel falsely „intermediate wheel“.

Edited by Kalanag
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Zandr Member

Zandr

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Just now, Kalanag said:

You are absolutely right! Sorry for my confusing comment!

No worries, naming on all this stuff is inconsistent at best, *especially* if you start looking at names in other languages.

I looked back at that ETA 2824 tech sheet and it does indeed call what we're describing as the second wheel an "Intermediate Wheel". It calls the fourth wheel a "Second Wheel", which is deeply confusing in English, but more obvious in German ('Sekundenrad' not 'zwieter Rad').

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