Hey all I was just cleaning the caseback on my seiko 6105 the other day and noticed that the lip had very fine concentric circle graining. I was wondering if that was for watertightness purposes or whether it was a product of the manufacturing process. Interesting. Also, what's more water tight - brushed or polished case lips? I can think of arguments for both...
Forgot to mention... probably negligible practical differences re the brushed v polished Only theoritical.
Yes, would be much more interesting too - alas I am at work but will update. In the meantime, the graining honestly reminds me of the monkey's tail of the Nazca Lines.
The fit of the o-ring and surface profile of the seating surfaces of the o-ring groove have the most to do with water-tightness (once the engineering is set). What this means is once the engineer(s) determine the thickness of the parts, (the o-ring groove size, the o-ring size, material and condition), it is a matter of the contact of the o-ring to the surfaces. Properly engineered, the pressure of the water bearing on the o-ring causes it to seal tighter. This is true to a point. Which ever profile provides the best contact is the best for water-tightness. Polished. For reference, I used to do engineering on submarine watertight boundaries.
This discussion needs Richard Feynman explaining why the Challenger O-rings failed and it blew up....
In the Naval Fleet Maintenance world there are many organizations providing technical direction/guidance/policies, etc. I was one of many (thousands of) engineers working on subs, using all the guidance that came before me, prepared by others. The world of a shipyard engineer is one of using tech manuals and powers of observation. We repair or maintain what others designed, in accordance with existing direction (even though I worked in the Design and Nuclear Engineering Divisions). What I'm saying is I had a lot of help and very little allowance to ad lib anything. If you do a search of SUBSAFE, you'll get an idea of how things were and are. I like my past experience, but am happy to be on the civilian side of things now. The pace is a lot faster and the need to rely upon my own judgement is more pronounced.
Brushed? Or are you just referring to superficial lines left by a cutting tool? The surface finish left by a machining operation depends on a lot of factors, including the condition and shape of the tool and the care taken with the operation. I think that high-end watch manufacturers are more likely to make efforts to leave a very smooth surface finish, while mid-range watch manufacturers presumably take a more utilitarian approach, especially for hidden surfaces.
You want: Smooth. Planar groove surface. Planar case back where o-ring contacts. Then you want planes parallel of both case groove and case back where 0-ring contacts. And all the previous mentioned regarding depth, o-ring cross section and o-ring material. So concentric lines sound like course machining.
In engineering terms, this doesn't mean anything. If you want to be specific with regards to surface finish tolerances, this is a general guideline... For a static mating surface: Ra 16-32 µinch For a dynamic mating surface: Ra 8-16 µinch Note that for the case back seal, this would be a static "face" style application, so the surface finish requirement is not terribly high. The crown could be considered dynamic, however that is typically referring to an application like a reciprocating piston, or some higher speed rotary application. The crown is a bit of both since in moves in and out from the case, but also rotates, but the speed/frequency is very low for both. Cheers, Al (watchmaker and engineer)
I realize that "smooth" is subjective but I hoped that all interested could envision a maybe shiny unlined surface versus the stated one with machine lines or grooves. I doubt many understand your surface call outs in micro inches but it is interesting and gives something those interested could track down and learn. I mentioned that the mating surfaces that trap the o-ring need to be parallel (again I do not call out how parallel as the drawing would say that the case designer used) I was not clear but just pointed this out cuz if the case back screws on crooked then one side could be higher than the other and maybe the o-ring would not be captured very well, but then again the 0-ring cross section can be designed to take up that imperfection. I would think that a screw down crown is static like the back and that a non-screw down crown is dynamic but non-screw down design is not usually considered very water tight. Oh, and I'm not sure a simple annular groove, 0-ring and case back make for a pressure assisted seal. Can we talk about the press (interference) fit of the crystal next or is it sealed with a gasket or adhesive....
If you simply look at any case back, you can clearly see the lines from machining. Here's an example of an SMP (25318000) and the surface where the O-ring seats is not shiny...machining marks are clearly visible on the surface that contacts the seal (it is a bit dirty though): And here is a Tudor Pelagos case back for a different brand - same thing the surface in question is not shiny or polished: Well since the thread was addressed specifically to engineers (and yes tinkerers too), I thought I would give a proper engineering answer that provides something other than subjective information. The thread pitch would have to be VERY fine in order to have the O-ring cross section take up the gap from cross threading - this really isn't a design consideration to be honest. What are you basing this on? Do you know how the crown seal works? To use Omega dive watches as an example (same sort of SMP as above), there is a seal inside the crown the contacts the outside diameter of the case tube - that seal is in contact with the case tube at all times, no matter what position the crown is in, so fully screwed in, out to position 1 for winding, out to position 2 for calendar quick adjust, and out to position 3 for time setting. The crown does not have to be screwed down for the watch to have water resistance - again a quartz SMP for example: Pressure tested with crown fully screwed down: Passed using the dive watch program, so -0.7 bar vacuum, and +10 bar pressure: Crown is now unscrewed to the first position - this position doesn't actually do anything on this watch): Tested and passed: Pulled out as far as the crown will go, so all the way out to the time setting position: Tested and passed: Here's another SMP doing the same test, but this one is an automatic: So the idea that a screw down crown's seal would be static doesn't make any sense - it is in contact with the case tube when the crown is moving in and out from the case, and also every time you wind or adjust the watch. So it is being flexed as the crown is turned or moved in and out from the case - it is not static at all times. There are some crown designs that use an additional seal that butts up against the end of the case tube, so those do provide more sealing when the crown is screwed down, but many don't. BTW there are plenty of non-screw down crown watches that are rated for 100 m, and I'm sure some that are rated for more. For example the DeVille automatics that with the earlier co-axial movements were rated for 100 m and didn't have screw down crowns. Advert for reference to the sort of watch I'm referring to (Ref. 45333100): https://www.amazon.ca/Omega-Deville-Coaxial-Watch-4533-31-00/dp/B000K1ZLPI And the same applies to most non-screw down crowns - the crown seal is in contact with the case tube at all times. Here is the same test done using a Speedmaster: Pressure testing passed even with the crown pulled out to the time setting position. I don't know what you mean specifically by pressure assisted seal, but a "simple annular groove, O-ring, and case back" are pretty much the standard method of sealing a wrist watch case back, and this goes for watches that are rated for very high depths, so 1000 m plus - deeper than humans go in the water...here is a Sinn U2 for example - good to 2000 m: Simple annular groove, O-ring, and case back: If you want to talk about the crystal we can certainly. Most dive watches are fitted with a thick crystal that is held in place by a hard plastic gasket. This gasket is deformed when the crystal is installed, and the gasket is a one use only item. Some watchmakers who may not have access to parts will sometimes use the crystal gasket again, but that is a veryt bad idea - the friction created after the gasket has been deformed once is just not as good as it is the first time. Here is an example of another SMP that came into my shop and I pressure tested it on arrival: It initially passed the vacuum test, but failed the pressure test: I used the extended leak finder test (extended pressure applied to case) in an effort to determine where the leak was: It initially passed the testing - here the pressure is dropping inside the test chamber: As the chamber was depressurizing, I heard a sound, and the chamber opened the crystal had popped out: Inadequate friction between the seal and the crystal, most likely due to using the seal over again: So a new gasket was used: The sides of the crystal are textured, and this helps hold the crystal in place - along with a relatively heavy interference fit: Pressing it in place: Passed fine: Note that when you press in a thick crystal like this with a tall gasket, and heavy interference fit, you need to seat the crystal rwice. The gasket will "relax" a but after the initial pressing in of the crystal, and this will push the crystal out slightly. After 1q5 minutes or so, you should go back and seat the crystal again, and you will hear a click - this video shows the second seating of the crystal installation and you can hear the click: There are other methods for securing a crystal in a watch, but again this type of hard plastic gasket is by far the most common with brands like Omega. I hope this helps shed some light on this subject for you, and maybe dispels some misconceptions you may have had. Cheers, Al
When diving wouldn't the crown seal be static (you would not be turning or pulling it out)? Especially if a screw down type and it is screwed tight as is the case back? I was just pointing out that the case back needs to mate parallel to the seal surface in the head. It was addressed to engineers but don't think we need to even reply if we are just answering to ourselves. As far as calling out surface requirements, Ra, the average of the peaks and valleys could be explained to the rest if you care to bring them along for the ride. I really do not know much about watch cases, especially newer dive types but the seals I worked on required extremely smooth surfaces and were even silver plated so the sharp edged lip of the seal would contact the sealing surfaces quite well. And fitting to this forum it was referred to as an "omega" seal because that was its cross section. The concave side faced toward the high pressure and it was a pressure activated seal as the gasses filled the inside of the curved portion of the "omega" and expanded the ridges to the sealing surfaces. I like your crystal pics and seal explanation. None of my Omega dive watches have a seal. Too old. Maybe my Marine Standard? But its crown is its Achilles heel.
Well, your initial comment was this... So what doesn’t make any sense is to say a screw down crown is static and a non-screw down crown is dynamic. That was the context of my answer. But with your new context, both styles of crown are static when not being moved but dynamic when being moved. I don’t agree with this definition by the way...a static application is the case back, where the back is screwed down and it stays that way until the case is opened. To me a dynamic application is one in which wear is a consideration, such as a crown, pushers, etc. that are moving frequently. By the way the other type of seal system you are describing is a different thing to a simple O-ring. I’ve dealt with lots of lip style seals as well, but those tend to be used in more high speed rotational situations, at least in my experience in industrial applications. On those surface finish of the sealing area is much more important, and I suspect the “silver plating” was likely a hard chrome, rather than silver. We used to have machine tools with hydrostatic bearings in them, so the spindle that the grinding wheel was mounted to would float on a film of high pressure oil, and lip seals would be used on the spindle to keep that high pressure oil in place. That area was subject to high wear, and spray chrome and rearing was a typical repair procedure. Cheers, Al
Ahh, I see my screw down vs non screw down inconsistency. I still think that when diving that it would be considered static but I guess in every day usage such as in the rain that the non screw down would be dynamic. No, the omega seal is used in a cryogenic plumbing flange on an upper state liquid hydrogen/liquid oxygen fueled rocket engine and I was just using it as an example as to an extremely smooth seal surface. It is not a lip or flange seal as used in rotating machinery. I guess this info is not so useful here with our simple watch and o-ring. Think of the omega (the seal's cross section) on its side between the two mating surfaces like our seal groove bottom and case back flange. Since it was a line on surface contact and tolerances were so high it actually was silver plated. The little feet tips of the omega dig in (on a very magnified scale). Kind of an old proprietary pressure assisted seal design that was costly to implement. Money is no cost on a 3.5 million dollar engine that sees more service on the test stand for validation than it does running on its mission. An interesting thing to show would be a pic of an example of the surface spec you stated earlier in relation to the original case we're supposed to be talking about. I must apologize as I have gone a bit afield.
This is a very odd way of thinking about this in my view. You appear to be thinking in a ":minute by minute" way, rather than looking more generally at the application. In your example any seal that isn't moving at a specific point in time is static, and when it's moving it's dynamic. That's not really how design is done, but if that is the way that helps you understand things, have at it. I'm not sure many people use their non-screw down crowns while out in the rain, but hey maybe it rains a lot where you live...odd... A "bit" afield? Yes I think so...