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By LittleWatchShop · Posted
I picked a nice ST 124 for $75. It is very very close to the E701 electric clock (I have serviced maybe four or five), so I am familiar with all of the little calibrations you must do during assembly. This is the first fully spring-driven version I have worked on. The mainsprings were a real pain. The barrels are riveted in, so I did not think I could use the mainspring tool, so I did it by hand. It was not horrible, but challenging. Anyway, it is done now. In retrospect, there might have been a way to do this on the winder if I manufactured an arbor just for this purpose. Who knows. -
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By Michael1962 · Posted
To my untrained eyes, wheel 1 does not look too bad. Wheel 2 appears to be showing some wear on the left hand face of the teeth. Wheel 3 appears to be a little bit worse than wheel 2 in the same place. The faces on the pinion on wheel 3 appear to be rolled over/deformed as well. I'm not sure what the tooth profile should be, but I think the wheels are showing some wear. It might be the angle of the photos though. -
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Hi guys, Some of you who have been stuck down the rabbit hole of watchmaking know that a fair part of it is finding a solution to a particular problem, especially when it come to vintage watches and all their idiosyncrasies. And, to find the solution, some unorthodox approaches and methods are employed. I find a good watchmaker will find a way to overcome. So, I'm servicing this Tissot 784.2 and find the centre wheel jewel is toast. The flat side of the jewel which the centre wheel sits on is intact, but the oil sink/dial side is crumbling and half of it is gone. It might last this way for some time, but maybe not and I'm guessing more on the latter. When I pressed it out, it fell apart. I teach my students there are two golden rules of watchmaking. Rule one: You are like the S.A.S. with servicing. You are in and out with no one knowing you were ever there. Not leaving gnarled screw heads and scratched bridges, etc. Rule two: Always think and consider the next watchmaker who is going to work on the watch. Don't leave obvious problems, or bodge something together, knowing it will create problems for the next watchmaker who works on the movement. If rule one is adhered to, rule two covers itself. The point I'm making here is, I could have left the centre wheel jewel and it might have lasted, but that's leaving the problem for the next guy and not very SAS. For some reason Seitz have discontinued the jewel size I needed (Sods law!), so I found one in a scrap movement that was the correct inside diameter. 0.8 mm to take a 0.79 centre wheel arbor. The outside diameter of the replacement jewel was 1.5 mm, so I had to ream the centre hole a little bigger from 1.19 mm to 1.49 mm. The problem was the jewel was 0.4 mm deep, so sat proud on the dial side and stopped the cannon pinion from seating properly, as you can see from this photo. I needed the jewel to be 0.27 mm deep like the cracked old one. Now, synthetic jewels are made from aluminium oxide with some colouring thrown in. Aluminium oxide is what is coated on wet and dry paper and as I don't have a diamond honing wheel, I decided to glue a piece of 400 grit onto a blank 8 mm collet and glue the jewel to a faced off wax chuck. Make sure the jewel is off-centre. Then I used my 8 mm lathe to hone the jewel from 0.4 to 0.27 mm. I can only use a GIF, so here it is... Then I lay another jewel that is 0.4 mm deep next to the one I'm honing and compare how much has been honed. I use a feeler gauge between the wax chuck and the wet and dry to gauge how deep the jewel is, so when I remove the jewel from the chuck using acetone, I know it is pretty close to what I want and found on my bench micrometre that I had honed it to 0.275 mm, so 0.005 mm bigger, which I'll force myself to live with. 🤣 I was pretty impressed by the accuracy of doing this by eye with no CNC or even micrometre gauges whilst honing, just a rudimentary feeler gauge I made. Then I pressed in the jewel with a jewelling tool and set the correct end-shake for the centre wheel and ensured the cannon pinion sat correctly without touching the centre wheel jewel. There was no real need to polish the face of the jewel, as it isn't an acting surface, but could have done using the same method with different diamond micron pastes to get a mirror finish. The whole process probably took me close to an hour to figure out and work. Obviously the next time, it would be half as long. The diamond wheels would have made the job a lot quicker, as the wet and dry was wearing out making honing more difficult. I think with a diamond wheel, this could be done in a matter of minutes. A lot of the time was taken soaking the wax chuck in acetone and gently teasing the jewel away from the chuck. Because the jewel is so slim it is also very brittle and will easily break if this stage is rushed, so it's a matter of being patient and letting the acetone do its work and wipe away the melted superglue and gently prying it off with your fingers, not tweezers. You can't gauge how much pressure you are putting on the side of the jewel if you use tweezers. I could have saved myself time and effort by making a brass bush to fit, but I didn't like that idea I had robbed a jewel and broken one of my cardinal rules, which was more 'Dad's Army' rather than S.A.S.! It's a very similar way I hone down brass bushes, as parting them off on a lathe can't get total accuracy on the depth, so I finish them off like this. Now I've been successful using this method, I'm going to invest in some different grade diamond wheels for my lathe. These kind of skills and problem solving, I teach here in South London in evening first and second year courses. I hope this gives you ideas of overcoming obstacles and another reason to buy a lathe!
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