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How A Chronometer Works Part II |
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Articles -
Watchmasters Corner
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Written by Ziggy Zumba
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Page 1 of 4
The second part of Ziggyzumba's series where he takes apart a chronograph movement used in a replica watch. This article focuses on the sub-dials.
Chronograph movement – PART 2, Running seconds, 12-Hour Sub-DialsDisclaimer:
the information here is mine only, it is based on my experiences and findings servicing these
movements. It’s only my opinion, however, I have tried to illustrate and support my reasons
with real data and pictures to help you understand why I come to the conclusions that I do.
That doesn’t mean I am right, it’s just how I see things. If you would like to offer a
different view, then it please support it with similar information to back it up for the
benefit of all reading this post. Posting a reply that “All Asian 7750’s are junk and will
break…” or “Don’t use the chronograph…” or something similar doesn’t help anyone without valid
reasons backing up your point of view.
I would like to add that every Asian 7750 that
I have serviced has been dirty, had pieces of metal in them floating around, and needed oiling,
especially the balance cap jewels. Once cleaned, oiled, and adjusted, they have all worked
fine. And the same goes for the seconds hand not resetting to “12” (you’ll see the fix later
on).
I am not advocating you have your 7750 serviced, that is a personal choice, but I
am also not going to state they are fine as delivered, because all the ones I have worked on,
aren’t.
Review
Before moving on to the actual chronograph, I wanted to
review what we covered in part 1, and simplify it so we can all understand and build a
chronograph from the basic movement. I know it’s hard to visualize this stuff without the
actual movement in you hand. I also realize that not everyone is familiar with how watches
work or what the parts and pieces do. This short review and pictures should help illustrate
these points.
Here’s the movement as assembled so far:
Here’s what all the parts are and what they do, and a
schematic of the basic movement (I did the CAD drawing on my new laptop my kids got for me,
it’s a “Etch-a-Sketch” brand, a bit slow, but works good….).
The only thing needed to make this watch work, is to install
a few more gears, and the balance wheel (I only install the balance wheel at the very end, it
is very fragile and I don’t want to risk damaging it during assembly).
The gears you
would need to install are these on the dial side of the watch, they take the motion from the
cannon pinion and transfer it to the hour and minute hands. Here are the gears, and some other
parts that make up the chrono part, we’ll see them later.
Dial side, gears etc to finish the basic watch.
So with these gears and the balance wheel in place, we have a
fully working watch movement. This however is a chronograph, so lets get started and turn it
into one.
Were going to install these parts first, they make up the basic chronograph
movement pieces.
Chronograph Cam and Levers
The heart of this
chronograph is the cam assembly. Before we move onto each sub-dial, lets review and understand
how this cam works. We will then add to this basic information and address each sub-dial in
detail.
The cam is the piece that starts, stops, and resets the chronograph, it controls
everything and looks simple enough, but serves and does many things at the same time. We are
going to examine each one in turn and at the end of it all, it will be easy to understand how
it all works.
Here is a view of the chronograph cam, and the upper and lower pusher
levers. Note that we are looking at the bottom of the movement in this view, it is upside
down.
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Last Updated ( Tuesday, 14 August 2007 )
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