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Inside the Seiko 6r15 with a comparison to the 7s26..

April 26 2009 at 2:22 PM
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Dr.Seiko  (Login DrSeiko)
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What follows is the final installment in a series of articals I started writing about the new Seiko "Scuba" divers watch and its caliber 6r15 some two years ago.


You can find the previous articals here:

Seiko SCUBA essay #1, the bezel

Seiko SCUBA essay #2 & 3, that gritty winding and a SAP!

This instalment is going to deal with the watches moter, or the new caliber 6r15 that Seiko originaly introduced in the Alpinist model in 2002 (?).

When Seiko first introduced the new model Alpinist, I may have been the very first to say: "Hey, wait a dogone minute there! Thats a 7s26!!

And it was`nt long before everyone else saw the same thing I saw and we all concluded that the new 6r15 WAS in fact a caliber based off Seiko`s mainstay, mainline, extreamly ubiquitous,,,,,,,,,,,,,,,,,,(Quite voice now) caliber 7s26.

But, the bigist questions still remained, LOL. HOW DID THEY DO THAT? How do you stuff handwinding and hacking parts in a caliber for that all intense purposes, is already pretty well stuffed. happy.gif

So please follow along as I get elbow deep in one of Seiko`s newest calibers, and find the answers to these pressing Seikoholic questions.
First, I ask you to at least read the second previous essay. The handwinding system was partially covered in the second artical, and I wont try and incorperate it here, but I`ll refere you back to it.
Second, this essay is not going to be a new or improved review of Seiko`s caliber 7s26, John Davis has already done an excelent review of this proceding caliber. Because of this, many aspects that are general to both calibers wont be touched on at all. Rather, this essay`s focus is on how the 7s26 was modified to became the 6r15, or how the 6r15 was adapted from the base 7s26 movement. When direct comparisons are to be made, the 7s26 is always on the left, the 6r15 on the right.

The engine. Looks like a hot rodded 7s26 to me, LOL.


Your eyes are not lieing, that case has been blasted, happy.gif

Now with the movement out, dial and hands removed, we turn it over and look at the bottom plate (Top is bottom and bottom is top in watchmaking, OK).


What is truley interesting above, besides all the hardware that I`ll get to, is that Seiko has desgined this caliber to easily accept a day wheel with nothing more then simply needing to put it on. You can see the day wheel finger (Or click) which is held over from the 7s26, and the grove for the retaining collor on the hour wheel was also held over from the 7s26. As well, the day wheel driving finger has been left on the final drive wheel. So there you go guys, a MKII day-date dial and the appropriate parts, and you can easily have a day display in your Sumo, err, Scuba.

Before we get into the meat of the "Under dial" or bottom plate stuff, I want to turn it over again and compare its top plates to a 7s26. Yes, there is a definate 7s26 resembelance.


It is pretty obvious they are very closely related to each other when looking at both sides of the movement, and comparing the verious landmarks we can easily see.

OK, Back to the front, err, bottom plate. Front is bottom and Back is Top, happy.gif



The two movements are virtually indentical except for that area right above where the stem comes into the movement. This is the redesigned "winding works" and we`ll get into that right now............


There are two seperate pinions above, which to most watchmakers will be a real surprise. Its usually assumed that one pinion can do the jobs of winding, setting, and changing the date, but in this case Seiko had to use two seperate pinions due to the fact that they where redesigning an already existing caliber and this was the easiest-softist way to accomplish the objectives of providing both handwinding and hacking in the redesigned movement. The pinon on the left is only for winding, and only comes into play (is Connected) when the crown is in the first position, this transfers windng rotation up to the rocker wheels that we will get into in a bit. Its really the date change mechanism that takes the cake here, what a way to do it! Build a bridge so that the date changing train can go up, around, and in front of the pinon that its being driven off!! There are no fewer then SEVEN seperate wheels involved in changing the date here!! I bet you had no idea you were pushing that many wheels, LOL. We`ll take that hold down plate off and you can see how these all mesh...........


OK, So we`ve figured out the date change, but how does that second pinon, moved so far towards the inside of the movement, wind the watch? You have to remove the top plate on the other side of the movement to find out.

Here is the top plate at the back of the movement with the "rocking" winding system expossed, and this is where I`ll refere you to essay #3 so that you know how this design and its parts work. It is this train plate/peice that I`m going to remove and turn over now so that you can see what completes the winding train in Seiko`s re-design, and where the last connection in this winding train is.


And I`ll remove it and turn it over now, so you can see what those above wheels are doing on the bottom side of this plate.


And there you have it, this is how is winds. That wheel under there is connected to the winding pinon that we see on the front dial side, and completes the handwinding train connection. All in all, this is actually pretty simple and straight forward, Seiko only needed to design a new top plate to hold the rocking parts and then a few stem parts to engage with them. This is IMHO, pretty accademic if you dont include that bridge. Again, its that bridge that takes the cake as far as "How we gonna do it" and then getting it done. Seiko really outdid themselves, Yes?

OK, so that takes care of how Seiko made the 7s26 handwind. But how does it hack?............................

With that top train plate above removed from the movement, its not immediately obvious how they accomplished the HACKING! "I seeeee nothing" said Shultz, LOL.


Stop looking, cause you wont see it. To see whats going on you have to remove the balance, but before I remove it, let me talk about the balance right quick........


Above we can see Seiko`s new Balance spring "pinning" system. It not only looks just like the ETA pining system, its just as ajustable! This leads me to believe that Seiko plans on making this caliber (or a sibling) into a chronometer grade watch at some point. It`s just too refined a system to languish in the base 7s26`s and their derivatives forever, for no reason happy.gif

OK, by pulling the balance cock off we can start to see where the hacking lever is.............


There it is! Right above the pallet fork. Notice that large-ish post sticking up vertically, that is what is used to stop the balance.

We now have to continue to remove the rest of the base 7s26 guts to see how it connects to the stem. Oh yes, the guts are pretty much ALL 7s26, happy.gif.


And there it is. Again, all in all, it is pretty simple and straight forward. While it may ride towards the outside of the movement much like a 4500 GS caliber, it does`nt have the complications of extra linkage points the 4500 does.

Looking at the stem end of the lever gives us a better idea of how it works............


As you can see, the ball rides through the elongated socket and moves the lever in and out towards the balance. I believe the extra fine side of the socket is there so as to add some gentalness to the system, but I`m just guessing this is why it (That end of the lever) is so thin?

What I find truley remarkable, is the way Seiko had to machine the plate in order to get this hacking lever to where is has to go, and how they got it all under the existing setting detent parts that are all part of the base 7s26 caliber. Now, keep in mind that when I`m at the bench, I look at everything through a 10X loupe, as the great watchmaker Homer Barkus once said: "I spend my life in a one inch world." So true Homer, LOL. And so this simple machining had a great impact on me when I first saw it. I call it "The Trench". What is truely remarklable about this trench is the fact thats its machined to within a few fractions of a MM from going all the way through the plate. THIS IS PRECISION machining here folks!!!!


And to sum up! One last comparison to the 7s26 base plate, totally NAKED!


And so that is it Gentalmen, this is how Seiko turned the watch world, and their own 7s26, totally on its head, and made the 6r15, happy.gif

I truely hope you enjoyed this last artical on the Seiko Scuba and its redesigned moter, and I hope you can appriciate Seiko even more now! What is very interesting to note to this watch machanic, is that this is`nt the first time Seiko has done this. The 6106 becomes the highly regarded 6159. The 5106 becomes the lowely 5123. The 6309 becomes the 6306, ect, ect. Seiko has always left room, one way or the other, to either down grade a movement or up grade a movement. What is remarkable to this watchmaker is that in Seiko`s history, they usually created the higher grade caliber first (Think Bellmatics, the 27 came first, then the 21, and then a whole slew of 17 jewlers) and then they continued to down grade the movement until the simplist form could be acchieved. But in this movement, a movement that has been in production for over 20 years, they did it the opisite way around, upgrading a movement that had been in production for 20+ years. To my knowledge, Seiko has never redesigned a base movement after 20+ years, except maybe the 52xx into the 4s24 stream (The 52XX caliber was never originally a handwind), and even then, there was virtually no actual redesign of the base 52xx, all but some minor balance sizing specs where held over in that redo and the autowind parts were simply left out.

And DON NOT forget to read the belowe post where we see exactly where Seiko is taking this new movement, another first for the lowely 7s26 base!!

The 6r15 gets to be a CHRONOGRAPH!

On a more personal NOTE. It has been strongly suggested by myself that Seiko should not have gone with a completely new caliber number for this movement. But I now feel that Seiko did so much to the base plate, so much redesigning, that it is COMPLETELY deserving of a totally new caliber designation. The two base plates WILL not interchange, but most of the guts will, happy.gif


Seikoholic #1
Dr.Seiko, Aka:2manywatches
Specializing in Seikology, Seikotherapy, and other Horological Dis-ease.
Made in the U.S.A.

This message has been edited by DrSeiko from IP address on Apr 28, 2009 11:45 AM

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