The watch is going to need some sort of protection against water and dust. I'm not planning on making this a diving watch but some sort of gasket mechanism needs to be put into place.

This is an experimental project, so I'm using what I've got to hand to make the components. So I'm using a cut-off tool (ground a bit slimmer at the cut-off end) to put a groove into the top watch section. The groove will hold the rubber gasket just proud enough to make a seal when the watch components are screwed together.

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I didn't do a very good job at my first attempt and got a lot of chatter due to my not positioning the tool correctly as you can see in the following photo:

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I put the ring back on the lathe and adjusted the tool. The next cut was much better, with no chatter, however, I could see that I was getting too close to the screw hole shafts that are inside the top section sides (see this earlier post on putting in the screw shafts).

 Here's the top watch section with the gasket in place:

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Now check the top and middle section fit together,

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yes they do, with a bit of pressure! I didn't leave much play between the two sections so with the gasket in place too it makes the sections fit together very snugly. Here's the view from the side

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That's great, now I need to make, and fit, the bottom section of the watch.