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onzenuub

A Solution for the Sunken DW of the Asian 7750

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onzenuub

From Fransico on RG etc.

 

Some gen watches employ an ETA 7753 movement. This movement is quite similar to ETA 7750, but the minute counter is at 3 position, whilst 7750 has the minute counter at 12.

 

As there is no rep of the 7753 movement, reps factories use a modification of the Asian 7750. This mod moves the minutes from 12 to 3. However, this mod produces a sunken Date Wheel (DW). Therefore, it is very easy to detect that the watch is a rep.

 

The objective of this tuto is to solve the problem of the sunken DW of modified Asian 7750, to move the minutes from 12 to 3, simulating a 7753.

 

First of all, let us check the final result, to clarify the objective.

 

Before the tuto:

3576037013_bbeef8d6e5.jpg

After:

3576842232_17684cb58c.jpg

 

Let us find out why the DW is sunken and how we can solve it. Next picture shows better the sunken DW problem:

 

3576842270_451185d722.jpg

After removing the dial, the modification is visible. With 3 gears is possible to move the minutes from 12 to 3. However, the DW is below these gears, and that is the origin of the problem we want to solve.

3576037215_faface9d11.jpg

 

The solution consists of placing another DW on the top of the gears, just at the same level as the DW is in the 7753, very close to the dial.

 

However, next picture shows the problem…. There is very little space available … it is a very complicated mod…

 

3576037441_b5d1f2282a.jpg

 

There is only 0.8 mm from the DW to the top of the movement. And the gears take aprox. half of this distance.

 

The idea is the following. We are going to manufacture a ring that will be placed where the red circle shows in next picture:

 

3576037513_7375f1b709.jpg

 

This ring has to be taller than 0.4 mm, taller than the gears. However, let us remember that the total height is only 0.8mm and the new DW has to be placed on the top of the ring. The problem is that the DW has a height of 0.52 mm. Therefore, the total length of ring + DW will be more than 0.8 mm, and the DW will touch the dial. It is extremely complicated. Solution is to modify the top DW.

 

In addition, there is another problem. Next picture shows that if a DW is placed on the top of the gears, the teeth of the DW will touch in some places, and the top DW cannot rotate.

 

3576842760_bc9ff208f4.jpg

 

Therefore, the teeth have to be removed. Two tasks to be made: reducing the height of the DW and eliminating the teeth. And with extreme precision, because the total length has to be 0.8 mm.

 

 

1.- MAKING THE RING.

 

Material for the ring has to be very strong steel because the ring is extremely small. I have employed a watchmaker lathe. A normal lathe is not useful, due to the high precision required.

 

First step is to turn a steel tube. Here turning the exterior:

 

3576842830_4f997fed9d.jpg

 

Polishing:

 

3576037815_faf68693e6.jpg

 

Turning the inside face:

 

3576037867_ab787773d8.jpg

 

The final ring is really thin… 0.35 mm

 

3576037915_9813a230f0.jpg

 

And now we have to cut it. This is really complicated, due to the high precision required. After several trials I have found that the best way is employing the milling attachment of the lathe with a diamond cutting disk.

 

3576843168_5fbe150e51.jpg

 

Follows a video that shows how the ring is cut… Amazing.

 

 

A picture of the ring. It is a very small part… and it has to be very precise…look such a small dimensions…

 

3576843236_7e98ce2082.jpg

 

2.- MODDING THE TOP DW.

 

For the top DW I have employed an ETA 7750 DW. If the gen watch uses a special font DW, and the rep has this font, then we have to use this special DW for the top, and the ETA DW for the bottom.

 

Next picture shows the back of a gen ETA DW. It is golden, because the material employed is brass. The DW is fastened between a grinding wheel (white) and a washer (black). Numbers (font) of the DW are protected using a plastic. Next step it is to reduce the width of the DW.

 

3576843288_a90cea9577.jpg

 

This video shows how the width (or height) or the DW is reduced:

 

 

Next step is to take out the teeth. This is the last step, because the teeth are used for fastening the DW. Again the milling attachment is employed.

 

3576038145_fb8cd0e1a9.jpg

 

Finished parts:

 

3576843428_ab4325c441.jpg

 

3.- ASSEMBLING.

 

To glue the ring to the top DW I have employed Araldit 5 minutes

 

3576843478_54f0507c5e.jpg

 

To glue ring + top DW to the bottom DW I have employed Hypo Cement.

 

3576843548_1cc29fccd5.jpg

 

Before gluing, we have to check that everything fits well:

 

3576843630_cfffbb6802.jpg

 

And we have to check that the minute counter works well, i. e., the top DW is not touching the gears of the mod.

 

Last step is to glue the top DW with ring to the bottom DW. Employing Hypo Cement or similar we have time enough to adjust the position of the top DW. This is an easy task…you only have to rotate it. The tight tolerances place the top DW is its correct position, you only have to rotate it.

 

And this video shows the final result:

 

 

The original idea of this tuto is from my colleagues Okabum and Vikingo. Thanks, friends.

 

Francisco.

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greg_r

wow. just wow. :D

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Luthier

More complicated and precise than heart surgery. Simply fantastic.

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jameo210369

I think a good watchsmith would make a great heart surgeon, I would imagine the watchsmith has steadier hands.

 

Love the thread Onze, :D

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oscarmadfish

great stuff

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FilBack

Would this work on a TAG Grand Carrera Calibre 36?

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Caliper

I assume you're referring to the calibre 36 RS2.

Additional gears were added to allow the A7750 to have the model watch dial configuration thus the sunken wheel. A solution like this could work, but the dials have wheels instead of hands, so the wheels could interfere with the raised datewheel, serious modding is to be done. Good luck.

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FilBack

I assume you're referring to the calibre 36 RS2.

Additional gears were added to allow the A7750 to have the model watch dial configuration thus the sunken wheel. A solution like this could work, but the dials have wheels instead of hands, so the wheels could interfere with the raised datewheel, serious modding is to be done. Good luck.

 

Ha Ha, not me! I never even opened a non quartz watch in my life before. I was thinking about buying one and sending it to someone who could do it.

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UmpaHimself
wow. just wow. :D

 

Nuff said. When I opened this tut I thought it would be something I could tackle... NOPE. You are elite my friend

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SSTEEL

I'm currently carrying out this mod, with the exception I don't have a lathe :P Thanks for reposting the tutorial Onze mate, the photos and videos links don't work next door, so this was really helpful.

 

What I have done due to not having that all important lathe (yet) is to reduce the outside diameter of the lower date wheel, and fitted a crystal gasket to the circumference. This not only gives me the clearance of those additional gears, but also is light enough, and a continuous ring for the piggyback date wheel to adhere to.

 

The removal of the top date wheel teeth will be a challenge, but will have to do it manually with my dremel tool somehow.

 

Here's a few photos of my method..

 

15846742550_36b2057cee.jpgUntitled by Micky.!, on Flickr

 

15846571528_c2752b4b26.jpgUntitled by Micky.!, on Flickr

 

I had to painstakingly reduce the outer diameter again once the gasket was fitted, this was easier than having to thin it out loose.

 

15412141654_b91f73c1ab.jpgUntitled by Micky.!, on Flickr

 

Anyway, I am still in the process of perfecting the above method, but will let you know how I get on. Oh, and just for fun, here's a few failed attempts :lol:

 

15802508108_4858692030.jpgUntitled by Micky.!, on Flickr

 

15810947929_a17a337d56.jpgUntitled by Micky.!, on Flickr

 

16003277315_865161f4af.jpgUntitled by Micky.!, on Flickr

 

My next big investment in watchmaking will for sure be a lathe.

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kennycoder

If this works out all right, you will have my navi with you immediately :D

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SSTEEL

Its a Navi that I'm doing this for :)

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pfcdre

Very impressive job, well done mate, how has the timekeeping been since the mod? just interested if the added load has cause any drag on the running gear. cheers

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SSTEEL

Thanks.

 

Its not finished yet, and if all goes well it won't impede the timekeeping at all. Using a Hytrel rather than a metal ring is lighter, so should be fine

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BentleySharp

Holy Mazoly. What an ingenious solution to the sunken datewheel problem. My hat goes off to you.

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aitcharGMT

Wow, @Francisco, incredible! I had been looking for this thread for a long time until @Glaude pointed me to it! (Thanks!). Unfortunately I was stupid enough to associate it with Navitimer when it's all 369 w/a7750 watches that have the issue. So here I go: Breitling, Navitimer, sunken date mod (modification), Montblanc Timewalker 7750. No date pusher. (Hope that makes it easier to find.)

(Now to find why the 7753 (a7753) won't fit on a Navitimer case.)

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