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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 3 of 4
This is a very special gear that although at first glance looks simple, is far from it. Lets
see what it does and how.
The 12-hour gear consists of 4 individual pieces, the bottom
gear which engages and is driven by the mainspring barrel, a clutch assembly, a heart piece for
resetting the gear to center, and a notched wheel that acts as a brake disk.
So how does it all work? Lets get started.
First off,
I said the mainspring barrel always turns when the watch is running. Then I added that this
part of the 12-hour gear was connected to the mainspring gear at all times, so that should tell
you that the 12-hour gear is always turning. Here’s a view of the gear in place and some
information.
This gear would always turn if we did not hold it in place
with a brake lever and clutch assembly.
The top half of the gear has a wheel with
“notches” around the outside edge, these are not gear teeth, but brake notches.
When the chronograph is OFF, this lever presses on the side
of the gear, and holds the top half stationary. The bottom half will continue to turn as long
as the watch is running. This is where the clutch comes in, it allows the top half to remain
fixed, while the bottom spins around - 2 times a day. If the chronograph is OFF, this clutch
is slipping all the time.
The bad part is that so far, I have not seen any lubricant
on this clutch, or the one on the cannon pinion (they are both the same type of design). As
you can see here, I have added some grease to lubricate this part and prevent wear, if it wears
out, then the sub-dial will not turn when the chronograph is ON, as it will be
slipping.
Now lets see what moves this plastic brake lever over. It is
connected into this arm here and moved by………..you guessed it, the cam assembly.
Here’s how it’s done:
When the chronograph is OFF, the
cam turns the shaft that engages the brake lever.
When the chronograph is ON, the cam turns again, and releases
the brake lever
When the chronograph is Stopped, the cam sets the brake
again
The metal arm that the plastic lever is connected
to is the reset lever for the 12-hour sub-dial. This lever is activated by the bottom pusher;
but only when the cam is in the OFF position, see here:
OFF position, note how the two tabs are lined up. The piece
next to the levers is the bottom pusher lever, remember it from the first views of the
cam.
In the ON or Running position, the lever is like
this, the two tabs are not lined up, and pressing on the bottom pusher does
nothing.
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Last Updated ( Tuesday, 14 August 2007 )
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