Opening a screw-back watch case is fairly a straightforward operation and allows you to change the battery on a quartz watch (so long as that watch has a screw-back case) or diagnose some common issues on a mechanical watch (so long as you know what you’re looking for, but that’s a subject for another post). Understand that this procedure takes some finesse and patience (and that if you’re not careful, you can scratch your watch case back), but that once you learn how to do it, it’s fairly easy to do, and can help save you a big tab at your local watchmaker – just try not to leave the case back off the watch for too long, as you’re only inviting the ingress of dust, hair, and all sorts of other gunk into a very delicate mechanical system.
Acquire The Appropriate Tools. While you don’t need to invest hundreds of dollars in the grade of tools that the pros use, there are a few things that are essential if you want to open your own case back (see the Buying Guide below). At minimum, a friction ball, case back wrench, case holder and common shop vice will make your life easier (you could conceivably do without the case holder and vice, but if you want to drastically reduce the likelihood of scratching a case back, we highly recommend them. Besides, you should have a shop vice lying around already – what kind of man doesn’t have a shop vice?)
Use the friction ball. If the case back hasn’t been tightened down to the watch case all the way, you can use that handy, inexpensive friction ball to open it. In this case, simply flip the watch over, grip it in one hand by the watch strap, and hold the friction ball against the case back with your other hand. Apply some pressure and rotate the ball counter-clockwise – if the case back is loose enough, it should unscrew fairly easily.
Set up your workspace. If the friction ball didn’t yield results, chances are the last guy who tinkered with your watch screwed the case back on there all the way, and in this case, you’re going to have to use the case back wrench to open it. First things first: take your case holder and place it in your shop vice, securing it in place so that it doesn’t move around. Then, place your watch (dial-down) in the case holder and tighten the nylon pins to secure it (if you want to be sure of not marring the case at all, we recommend putting down a cleaning cloth onto the pins before placing your watch in the holder).
Set up the case wrench. While it’s likely best to invest in a finer, Jaxa or LG-designed case back wrench if you’re a professional watchmaker, a less expensive version is generally fine for our purposes (keep in mind that the cheaper the tool, the more quickly and likely the threading will strip). Your wrench will likely come with several different types of chucks, which are the small pieces that fit into the actual grooves on your case back (some are polygonal, some slotted, some are small holes, etc.). Find the type that match up with the grooves on your case back and screw them into the three threaded slots on your wrench – make sure you screw each one in all the way, or they will be at different heights, and you won’t be able to get a good grip on the case back.
Size the wrench. Okay, now begins the delicate part: in order to size the wrench to your particular watch’s case back, you have to first carefully hold the wrench over the case such that one of the chucks lines up with one of the case back grooves – this way you can see what kind of adjustments need to be made to the wrench (of course, this must be done carefully and with a steady hand, lest you slip and scratch the case back). Once you have one chuck lined up, size the wrench such that the chuck opposite the first one fits into the groove opposite it on the case back; this is done by adjusting a thumb-wheel on the wrench between the two chuck-holders. Now, carefully try fitting the chucks into the case back slots – if they don’t line up well, re-adjust the thumb wheel on the wrench until they do.
Begin opening the case back. At this point, if you find that you have a good grip on the case back with only the two chucks, you can try to open the back. Very carefully, holding the wrench steady in one hand and, while applying some mild downward pressure with the other hand, try moving the wrench counter-clockwise. If the case back is really stuck on there, you may need to affix a third chuck into the third chuck holder on the wrench and adjust until all three are slotted into grooves on the case back (in order to move the third chuck closer or farther from the other two, spin the handle on the case back wrench clockwise and counter-clockwise). Now you have three, evenly-spaced chucks gripping the case back, and the added surface area should help you get some leverage (again, just be careful not to let the chucks slip and scratch the case back!).
Open the case back with the ball. Once you’ve gotten the case back partially unscrewed, you can set the wrench down and use the friction ball to open it the rest of the way, without any risk of scratching it. If you’re working on a quartz watch, you can now change the battery, and if you’re working on a mechanical watch, you’re now free to do whatever it is you need to do in there (what exactly are you doing in there, just looking around for the pure fascination of it? Okay, fine – I’m guilty of doing this myself) – just keep in mind, again, that the longer the case back is off the case, the more opportunity there is for schmutz to get in there and gum up the movement (if you don’t know what “schmutz” is, go pick up a Yiddish dictionary – that’s your homework assignment for the day) – so don’t leave the case back off for too long. Do what you gotta do, and reverse these steps in order to screw it back on such that it forms a tight seal, but not so tight that it’ll be impossible to get back off again.
Here are some good options for the aforementioned tools:
Large Watch Movement & Case Holder by Esslinger $18
Watch Case Opening Friction Ball by Esslinger $6
Waterproof Watch Case Wrench by Esslinger $17
Microfiber Jewelery Polishing Cloth by Esslinger $3