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How A Chronometer Works Part III |
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Articles -
Watchmasters Corner
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Written by Ziggy Zumba
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Page 1 of 4
The final part in looking at an ETA 7750 used in a replica watch. Ziggy tears the movement apart to see how it ticks. He provides a detailed analysis as to its function and lifespan.
Part 2A, Chronograph Seconds Sub-Dial
OK, since this seems to be the 7750 weekend, lets carry on with our understanding of the workings of this movement.
Review time.
Due to the length of Part 2, I decided to leave this part out and use it here.
Remember this CAD drawing of the basic movement:
Well I have been busy adding the 12-hour display that we covered in detail last time to the drawing, now it’s fairly complex and you may want to have a beer or coffee and get ready to study the intricacies of this highly detailed and confusing diagram before moving on the next part.
Are you ready???
OK, here is the drawing of the 12-hour chrono sub-dial added to our movement.
Fairly complex isn’t it?? NO, and neither is the rest of it if we examine each part individually.
Main Chronograph Seconds display
This one is a bit more complex, so lets break it down into manageable pieces.
The main seconds Chronograph seconds display is the large center seconds hand on the dial.
Earlier we saw that the running seconds sub-dial comes from the 2nd wheel of the basic movement. So where do you think we get the input to drive the seconds gear for the chronograph??? If you did not answer the 2nd wheel, then you have failed the test (again), and…. well you know the drill…..send me all your watches…..
Remember the chronograph is simply add-on’s to the basic movement. Lets see how this one is done.
First off, we should know what the chronograph seconds hand going to do for us, it will display:
1. seconds
2. have the ability to start and stop when we want it to, and
3. be able to be reset to the “12” or zero position on the dial
Chronograph seconds are displayed on the center of the dial. Since the basic movement 2nd wheel is our source of motion for the chronograph seconds, we need a way to take the turning motion from the 2nd wheel to the chrono seconds wheel. We will do this with a new pinion (a pinion is a shaft with gear teeth on it, a wheel is the larger gear that mates with the pinion). This pinion has two sets of gear teeth on it, one on the bottom (to engage in the 2nd wheel) and one on the top (to transfer the motion to the chronograph seconds wheel).
This new gear is called a “tilting pinion” and here it is:
Here’s an ETA and Asian tilting pinion next to each other, guess which is which??
Here is the tilting pinion in place, note how it is taking the motion from the 2nd wheel
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Last Updated ( Tuesday, 14 August 2007 )
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