Most watch fans think that the most important to get a good sealing in diver are O-rings. They think that if there are two O-rings instead of one, the watch cases will be much more sealed. Although O-rings are important for sealed, with one is enough. What is important is that the contact surfaces of the middle case and the case back are well flattened. In Théorie de la construction horlogère pour ingénieurs the necessary parameters for a good surface finish are well described.
To have the best seal between two surfaces is do not allow water to pass to the watch case inside when is assembled. The O-ring that is placed between two surfaces is compressed and helps not to pass the water. However, two of the easiest factors of altering it are flattened surfaces and its finishing. From this subject there are two parameters to consider,
– Flattened defects should be less than 10%
– The quality of roughness between the two surfaces must be
N7 (Ra <1.6 μm and Rmax <3,2 μm ) for static sealing
N6 (Ra <0.8 μm and Rmax <1,6 μm ) for dynamic sealing
These defects are due to few machining time. A minimum of machining the surfaces to be assembled to flatten the surfaces, from a mold or turning or milling is needed. Hence, the well finished cases are more expensive due to the time of manufacture. In addition, to avoid unequal polished surfaces, often is used the vibratory finishing what allows to remove the surface material in a homogeneous way, without ending surfaces not flattened.
Finally, to measure the surface roughness profilometer is used. The device is applied directly to surfaces and data displayed on the screen. Data refer to Ra, Rz, Rmax, etc., that are most important to check the surface roughness.So the best sealing proceeds flatted surfaces or with the same, machining surfaces perfectly in order to get a good sealing watches diver