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Discussion Starter #1
So how hard would it be? I was reading a description of how the Bernhardt Instruments Globemaster modifies an ETA 2836-2. Why couldn't this be done on a 6309? Or am I showing a complete level of ignorance on how the 6309 controls day/date which perhaps differs completely from the ETA?

"The modification is really quite clever - in its native, unmodified form, the 2836-2 adds day of the week display capabilities to the 2824-2 - basically just a gear train which rotates a wheel a complete revolution once every 7 days. By modifying the gear ration of this gear train, it makes a complete rotation once every 24 hours. Replace the standard under-the-dial day of the week display wheel on the standard 2836-2 with an on-top-of-the-dial orange skeletonized 24 hour hand, and viola! You have yourself a watch with a 4th hand which can be independently set, and rotates around the dial once every 24 hours - giving the Globemaster very unique GMT functionality."
 

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I did this one a few years ago. Not a true GMT (ok more of a world time), but I can still tell the time on two timezones:

 

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Discussion Starter #4
She's a beaut Gabe but I'm thinking 4th hand and an Explorer II style bezel.
 

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Discussion Starter #5
TheTigerUK said:
It has been done !! Noah Riley did it a while ago, really nice.
Hmm...so is there any reason it couldn't be done on a 7S26? I'm thinking an SKX031/033 would be a great platform for it.
 

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Hi Saul,
The description you quote is overly simplified. The ETA 2836 has an instantaneous day/date change, meaning it changed over to the next day in an instant (and actually pushes the day disc ahead two steps each time, due to the bi-lingual day disc). Otherwise the day disc is not rotating at all. So there is more than a simple change in a "gear ration" (I think they meant "ratio" ;) ), they must also supply continuous rotative force to the 24 hour wheel. They also must supply some sort of mechanism that allows slippage between the driving force and the 24 hour wheel, so that it can be independently set at will as the description mentions. Both of these conditions necessitate access to manufacturing equipment and/or know-how to make such parts that aren't available off the shelf.


My 6309 GMT is a little different- it is a "simple" GMT in that the GMT hand cannot be independently offset from the 12 hour hand. I borrowed/ripped off the design from the earlier Seiko 6117 caliber (which is also a "simple" GMT watch), and then modified it to work in the 6309, which shares enough similarities with the 61xx stream that the existing infrastructure could be altered to fit everything inside. Here are more details:
http://www.thewatchsite.com/index.php/topic,432.0.html


It'd be nice to have independent setting for the 12 hour hand or 24 hour hand, but I'm still a ways off from that- I'd have to be able to manufacture some pretty complex parts to allow this, and find space to put them in the 6309 without altering it's height. I dream at night, but only dreams at this point. It kind of seems like a redundant project anyways as Seiko has an excellent Diver's watch with this feature already present, the SBDB001 Marine Master 600M GMT. The cost of this watch would be similar to custom-making the parts to do this in an automatic version, at least on a small scale, so it doesn't really make much sense to pursue.


The 7S26 doesn't have the same calendar system that the 6309 does, it is a little more compacted and there are a few components physically in the way of adding a 24 hour wheel. The simple answer is that the 7S26 is not an viable candidate for adding a GMT hand, at least without extensive manufacturing/re-manufacturing of parts.
 

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Discussion Starter #7
rileynp said:
Hi Saul,
The description you quote is overly simplified. The ETA 2836 has an instantaneous day/date change, meaning it changed over to the next day in an instant (and actually pushes the day disc ahead two steps each time, due to the bi-lingual day disc). Otherwise the day disc is not rotating at all. So there is more than a simple change in a "gear ration" (I think they meant "ratio" ;) ), they must also supply continuous rotative force to the 24 hour wheel. They also must supply some sort of mechanism that allows slippage between the driving force and the 24 hour wheel, so that it can be independently set at will as the description mentions. Both of these conditions necessitate access to manufacturing equipment and/or know-how to make such parts that aren't available off the shelf.


My 6309 GMT is a little different- it is a "simple" GMT in that the GMT hand cannot be independently offset from the 12 hour hand. I borrowed/ripped off the design from the earlier Seiko 6117 caliber (which is also a "simple" GMT watch), and then modified it to work in the 6309, which shares enough similarities with the 61xx stream that the existing infrastructure could be altered to fit everything inside. Here are more details:
http://www.thewatchsite.com/index.php/topic,432.0.html


It'd be nice to have independent setting for the 12 hour hand or 24 hour hand, but I'm still a ways off from that- I'd have to be able to manufacture some pretty complex parts to allow this, and find space to put them in the 6309 without altering it's height. I dream at night, but only dreams at this point. It kind of seems like a redundant project anyways as Seiko has an excellent Diver's watch with this feature already present, the SBDB001 Marine Master 600M GMT. The cost of this watch would be similar to custom-making the parts to do this in an automatic version, at least on a small scale, so it doesn't really make much sense to pursue.


The 7S26 doesn't have the same calendar system that the 6309 does, it is a little more compacted and there are a few components physically in the way of adding a 24 hour wheel. The simple answer is that the 7S26 is not an viable candidate for adding a GMT hand, at least without extensive manufacturing/re-manufacturing of parts.
Hey Noah, appreciate the feedback. I found your write up on the N54 mirror earlier this evening. Seems like a bit more work than I would have guessed. I also came to figure that modifications to the Globemaster were not really going to relate to a Seiko mod.

So the GMT hand on the 6117 was not independently settable? Hmm. I don't know where I'm really going with all this. I don't need a GMT but I have become enamored with the Rolex Explorer II aesthetic and I am having my doubts about the various Chinese clones. Well, we shall see. I love to tilt at windmills... ;D
 

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So the GMT hand on the 6117 was not independently settable? Hmm. I don't know where I'm really going with all this. I don't need a GMT but I have become enamored with the Rolex Explorer II aesthetic

Hi Saul,
That is correct, the 6117's 12-and 24-hour hands are linked and cannot be adjusted independently of each other. It's funny you mention the Exp II- the first model was also a "simple" GMT caliber (as was the first GMT-Master model)- and with the Exp II you couldn't even rotate the bezel- making the 24 hour hand not very useful for telling the time in another time zone. At least with a rotating bezel, one can set it to a desired time zone apart from their own. Later models of both the Exp II and GMT Master II's rectified this with independently settable 12-hour hands, and they are more complex in their construction on the dial side because of this added feature.


I find 24-hour hands are kind of like a seconds hand- no one really needs one, but once you have one, it's hard to go without (OK, slight joke). Your mention of windmills reminded me of this shot:
 

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Discussion Starter #9
I think I need to start by picking up a 6117 Navigator just to get a GMT on my wrist and work off some of this energy. If a complicated mod follows than so be it. Actually looked at an EXPII over the weekend at one of the large chain jewelers in the mall. Have the same complaint about the real thing as I do about most current generation Rolex "tool" watches. Dial is way too busy. If I had the $6K to spend on a swiss watch I would rather split it in half and pick up a vintage Speedmaster and Seamaster 300...ah well...always been more of an Omega freak...I wouldn't really mind a globemaster but I would have to factor in the cost of changing the dial and bead blasting the case...oh the curse of WIS-dom... :p

So as the GMT hand on a 6117 is linked to the hour hand, what determines it's positional relationship? Like, if it is 12:00, where is the GMT set?
 

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So as the GMT hand on a 6117 is linked to the hour hand, what determines it's positional relationship? Like, if it is 12:00, where is the GMT set?

If I understand your question, whatever relationship the watchmaker sets up when installing the hands is kept. Traditionally on "simple" GMT watches the 24 hour hand is installed so that 2400 is straight North on the dial, starting at the top and taking 24 hours to make one revolution. When it is 1200, the 24 hour hand is pointing directly South on the dial, when it is 1800, the 24 hour hand is pointing directly West, and so forth. Therefore when the 24 hour hand is on the left 1/2 of the dial, it is AM, and when it is on the right 1/2, it is PM. Here is another picture of a Mod that incorporates two 24-hour tracks, so that "home" 24 hour time can be kept via the dial track, and an "away" 24 hour time can be kept by rotating the bezel an appropriate offset of hours and reading whichever hour the 24 hour hand is pointing at on the bezel:

In this example, the local time is just shy of 1300 hours (1pm). The bezel is offset by 13 hours (when it is midnight at home, it is 1pm in the 2nd location), so at the 2nd time zone it is almost 0200 hours (2am).
 
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