How To Set Time On A 6498?

[Dave]

Hi,

 

Its a trivial question "How does setting the time work on a 6498?", but the penny has yet to drop. If anyone could add some detail I would be grateful.

 

I've assembled a couple of 6497 watches, and can appreciate how pulling out the stem moves the barrel and engages the two intermediate wheels.

I also know that the 6497 is non-hacking, so the second hand continues to move. *But* there is a constantly engaged set of wheels from the escape-wheel to the hour hand. How does setting the time not spin the second hand or jam the palette-fork?

 

I'm trying to expand the time-setting functionality to my 6498 Simulator, and I'm missing some details on how I've got the various components connected up.

 

 

Thanks,

Dave

[Geo]

Hi Dave, to clarify matter first, the part that is moved when you pull out the stem is called the clutch wheel. The barrel is the wheel that contains the mainspring.

Here is a very sussinct article on watch motion work where the operation of the cannon wheel is clearly described. Please note that I have copied this information in compliance with David Boettcher's copyright conditions by including :-

"Information from VintageWatchstraps.com © David Boettcher"

Motion Work

The motion work is a set of wheels under the dial that takes the motion of the centre wheel, which turns once an hour, and divides it by twelve to drive the hour hand.

The picture here shows how the motion works operates. The drive from the great wheel turns the centre wheel, coloured yellow. The rate at which this turns is of course governed by how quickly the escapement, through the "going train", allows it to turn, which is arranged to be once an hour. The arbor of the centre wheel is extended through the bottom plate and the dial and turns the cannon pinion, which carries the minute hand on a pipe extending from the pinion.

The pipe that carries the minute hand is what gives the cannon pinion its name. In watchwork a pinion is a small gear, such as the one at the base of the cannon pinion. Etymologically the word cannon means a 'large tube', derived from the Latin canna for reed, which also gives us the word 'cane' for tall grasses with hollow stems, especially bamboo or sugar cane. So the cannon pinion is simply a pinion with a large tube attached to it.

To drive the hour hand, the cannon pinion turns the minute wheel, which carries a smaller pinion that drives the hour wheel. Why this is called the minute wheel escapes me, because it neither carries the minute hand nor turns once a minute. But it has to be called something, and minute wheel it is.

The gearing of the cannon pinion to the minute wheel and the minute pinion to the hour wheel are arranged to give an overall 12:1 step down in turning speed, so that the hour wheel turns once in twelve hours. The hour hand is mounted on a pipe projecting from the hour wheel. Using the same logic as for the cannon pinion, this could have been called the cannon wheel, but it isn't.

The cannon pinion is a friction fit on the centre arbor so that the hands can be turned to set the time. The cannon pinion has a slight indent that snaps into a groove on the centre arbor as shown in the picture. This stops the cannon pinion from floating up and down on the centre arbor, and also provides the means by which the friction between the cannon pinion and the arbor is controlled. If the friction is too great, the hands cannot be set easily, but if it is too small the hands slip whilst the watch is working and don't indicate the correct time. The friction between the cannon pinion and the centre arbor is increased by lightly tapping the indent with a punch to make it grip tighter, or decreased by broaching the hole in the cannon pinion. To prevent the hour wheel from floating up and either rubbing on the dial or causing the hour hand to touch the crystal, a very thin concave brass dial washer is usually fitted as shown in the picture.

If a centre seconds hand is fitted, as is shown in the picture, this is driven separately and not connected to the motion work. It is driven either "indirectly" from the third wheel as shown in the picture, or "directly" by rearranging the layout of the movement to bring the arbor of the fourth wheel to the centre as described in the section about Centre Seconds elsewhere on this page.

If there is no centre seconds hand the centre wheel arbor is solid in modern movements. In older movements, mainly pocket watches and some very early wristwatches, a Lépine friction centre post was used to drive the cannon pinion. This replaced the extended arbor of the centre wheel with a post or pin fitted into a hole bored through the shortened arbor of the centre wheel. This pin is a friction fit into the hole in the centre wheel and drives the cannon pinion. Its purpose is to allow the hands to be set by a key from the back of the watch.

The friction centre post was invented by Jean Antoine Lépine in the eighteenth century. Before this invention the hands were set by applying a key directly to a square boss on top or front of the cannon pinion, which meant that the front of the case, the bezel carrying the crystal, had to be arranged to open, and also that there was the constant danger of the owner slipping with the key and marking the dial or damaging the hands. Lépine's invention allowed the bezel and crystal to be fixed to the middle part of the case, which made the case simpler, and allowed the crystal to have a lower dome, which made the case slimmer. This was just one of Lépine's contributions to the design of the modern watch.

[clockboy]

Absolutely brilliant  explanation Geo 5*****

 

You should be a teacher or least go to the top of the class.

[Geo]

Absolutely brilliant  explanation Geo 5*****

 

You should be a teacher or least go to the top of the class.

No credit to me Clockboy, it just happened to be the best explanation I have come across. That is why I double checked the conditions if copyright before posting. So all credit to David Boettcher! :)

[Dave]

Awesome, thanks. I hadn't appreciated the centre-pinion / cannon-pinion element before.

 

So everything from the barrel (correct use!), through the centre-pinion, to the escape wheel rotates from the power supplied by the mainspring. 

The canon-pinion rotates from the friction of the centre-pinion (and mainspring power), or from the setting wheels, whichever exerts the largest force.

 

Should be able to add all that to the program.

 

Thanks again,

Dave.

[Rob]

That's a very good explanation, and I have to agree with the special mention of how stupid the naming of the "minute wheel" is. This caused me a lot of headache when first trying to learn how a basic movement works. Since the hour wheel does indeed carry the hour hand one would assume that the minute wheel would carry or drive the minute hand but noooope.  :pulling-hair-out:

 

Anyways, that simulator app sounds fun. Any more details on it?

[Dave]

Anyways, that simulator app sounds fun. Any more details on it?

 

I started out getting frustrated that watch brands didn't quite produce what I wanted, so I started assembling my own (http://instagram.com/david.steadman/). Then I found that the parts available online weren't entirely right either. Sometimes the lume won't match or you could end up making an exploring-military-submariner. So I was motivated to explore other watchmaking ideas, and as a software engineer, my doodles (https://www.khanacademy.org/profile/DavidSteadman/programs) kept accumulating. So that's the starting point.

 

The picture above has a 4-by-5 rectangle around it. Thats the aspect ratio of the upcoming Apple Watch screen, thats the aspirational end point. Currently the software development kit can't handle a heavy-weight app, but it will be capable soon enough. If Apple lets the "genie out of the bottle" and allows people to design custom watchfaces, there will a rush of various styles. My only hope will be to have the most *legitimate* simulation around. So in everything I do, I want it to be real.

 

To that end, its a *real* simulation. The cogs all mesh properly, the balance wheel oscillations really flick the palette fork, and the whole thing winds-down and stops when the mainspring is empty.

 

The presentation is also real. There are no images or pre-canned resources. Its all drawn from first principles every time. The first iteration was some miscellaneous sin() and cos() calls. Its now a small maths framework of points and vectors, which perform over 10,000 trig calls to setup the view. The most complex bit is the mainspring. A dynamic-spiral which coils inwards or outwards depending on the charge, and maintains the same length (pretty much) throughout.

 

What you see above is the blueprint-mode, it also has a real-mode where I draw everything in a more photorealistic manner. The bridges are on the to-do list, along with so much else.

In terms of bluesky future-stuff... I can change the lume to glow when its dark. I could add a 24hour hand to a 6498. I have the chance to create my own watch designs and scratch-the-itch which started this train-of-thought.

[BlakeL]

I'm working on a 6498 right now so this is very interesting info.  That simulator looks awesome!  Would you share the code?  

Going to send you a request on Instagram.

Edited February 13, 2015 by BlakeL

[Geo]

That's clever stuff you're doing Dave, I'm well impressed! :)