onzenuub 308 Posted June 26, 2009 Found on another board: I took apart a 7750 and I got it back together again. Well, not entirely: we didn't take apart some of the chronometer subsections, basicaly due to time considerations, but we did get it completely apart (and yes, back together again). I thought I'd share this with y'all so you can see what many of you are wearing on your wrists and why the 7750 is just so doggarnded popular with watchmakers. Plus I finally had the equipment to do this right: all pictures taken with an Olympus E510, 35mm f3.5 macro lens, and a Bower SFRDL LED ring light to give some decent illumination in the basement of the Windecker shop. I've resized the pictures to 800x600 for posting purposes, but they've not been otherwise modified. They were also done with no other lighting, and to be honest I was concentrating more on working on the movement than taking the best possible photos... So what did we start with? This, of course: the 7750, in this case the top version from IWC. It's a schooling movement and has been taken apart probably around 50 times or so. Pretty spiffy if you ask me, and it's very similar to what is in my Guinand (which I wore on that day, of course!). Now, what is missing is the day wheel, but that's okay. You start not from the back of the movement, but rather from the front... So, you remove the screws from the date jumper maintaining plate... ...and remove the plate itself. Simple, stamped metal. Functional, but that's okay, no one ever sees it anyway. Remove the screw from the data indicator maintaining plate, and you can remove that plate as well... You also need to remove the jumpers spring, the day and date jumpers (the little things that move the day and date wheel one step), and the date indicator as well (aka date wheel). This shows the double connector (the gear with five teeth on the right-hand side) in all of its glory. You remove the 3 screws for the date platform and then gently remove the date platform in its entirety. You then remove the hour hammer spring, the hour counter lock, the hour hammer operating lever, the hour hammer itself, the hour counting wheel, the date indicator driving wheel, the day star driving wheel, the intermediate calendar wheel driving wheel, as well as the hour wheel and the minute wheel, the free cannon pinion, and you're done for the dial side of the movement and it looks like this: And these are the parts of the day/date stuff: At this point you have to turn the movement over to proceed further. I've already taken off the oscillating weight here... So, the hammer spring and the clutch spring are removed...and the screws for the automatic device bridge, then the bridge itself. Hammer, reversing wheel, minute counting wheel are gone, chronograph wheel, and that damned 60 minute oscillating pinion (this is a real to get back together!), and reduction wheel are off... And now the screw for the minute counter and the minute counter... ... and the screws for the chronograph bridge and the chrono bridge itself... Then you remove the ratchet wheel driving wheel, the chronograph wheel friction (Delrin plastic!) and you have... ... then the screws for the operating lever, the operating lever, lock, the minute counter driving wheel, the operating lever, the operating lever spring, the switch, the chronograph cam, the hammer cam jumper, and by this point the balance wheel assembly is gone as well. And you're left with the basis: This is all the parts: These are the date and day parts (missing the day dial...): Date platform with screws: Winding mechanism parts: Weight parts and other parts... Gearing and pinions, oh my! Chrono stuff... Balance, escapement, etc... Chrono assembly...this is what we didn't take apart due to time constraints. Attached to the barrel and train wheel bridge assembly. Mainspring, gear train and hack lever... And the perfect watchmaking work area: plain, simple, good lighting, clean and quiet, with right and proper tools, all at the right height... At this point it was lunch time: 4 hours had passed! We went for a brief lunch (it was a wet and miserable day), and then we came back to start putting it back together. First of all the mainspring and the gear train: Mainspring barrel, great wheel, third wheel, second wheel with long lower pivot, escape wheel... But actually you put in the barrel, then the escape wheel, then the second wheel, then the third wheel, and then the great wheel. The next part is difficult: you have to line up all the jeweled holes in the barrel and train wheel bridge with the gear train. This took me about 20 minutes and about 10 different attempts to do: Jürgen Windecker, the master watchmaker who gave the course, did it in three tries in about 4 minutes... Add then the balance wheel assembly. While this looks difficult, it actually goes pretty quickly if you've pre-aligned everything. The key is having the escapement slightly off-center engaging the escape wheel, and making sure that the pin on the balance staff is engaging the escapement. Took three tries, but it's pretty straightforward... The rest of the assembly is basically the disassembly reversed: My impression of the 7750? Built like a tank. There are a lot of small compromises to the design: lots of stamped parts, rather than milled, and the chronograph system is simply not very pretty compared to the nicer chronograph types. But it's built to be robust, to be fairly easy to work on - Windecker said basically that he can do a complete disassembly, clean, reassembly and lube, as well as basic timing, in around 4-5 hours, including 30 minutes in a cleaning machine for the parts. That makes it feasible, given labor costs, to make it possible to maintain the watch at a reasonable price. There are some damn tricky bits. Getting the bridge over the gear train ain't easy (this is usually true of most watches, though), getting the oscillating pinion to mesh properly with the chronograph wheel took me quite a while. On the dial side, you need to make sure that the day star and date indicator wheels point the right way, but this worked pretty well for me. Where I really sweated was getting the the day and date jumpers with the damn jumper spring in right and engaged into the date wheel! That took me close to 20 minutes, and just when I thought it was right, it locked up and I had to do it again. Learned a lot, mostly a huge amount of respect for the folks who do this on a daily basis, as well as for the engineers who designed it. For the real blow-by-blow disassembly and assembly, take a look here: http://www.eta.ch/swisslab/7750/7750.html This is the best way possible to figure out how things work: let the maker show you! And now for some criticism of the movement, which has to do with perhaps taking cost-cutting too far (in my opinion): this is, even in the higher grades of the movement, a modern mass-production movement that cuts corners very, very tightly in order to reduce costs. Take another look at this photo: Share this post Link to post Share on other sites
