I make a recess in the middle watch section to take the back piece. I'm cutting down 2.0mm into the back of the middle section to leave a 1.7mm thick shelf inside the middle section. This gives strength and acts as a border between the top and bottom watch sections but I think it could be slimmer in future.
The middle section wall thickness is 0.5mm, so it's important to make sure the middle watch section is properly centered on the lathe before making this cut.
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.
To cut the ellipsoid shape into the top ring section I've programmed the ellipse in g-code so that the lathe table will follow this shape. The cut gets incrementally closer to the final cut. In the diagram, above, the solid white lines are the tool paths yet to be followed and the red ones are the paths already done.
On the final cut I increase the lathe spindle speed to give the finest finish.
Going back over the photo's I remembered that I'd forgotten to include this bit, apologies about the 'part 10.5' but it fits between the part 10 and 11.
I'd like the edge of the watch-glass shelf to have some curvature so that it doesn't just end abruptly with a square edge. I'm going to use the lathe and some cnc to cut the curve.
Let's get the top of the watch finished, it's getting to look more and more like a watch so I'm getting quite excited!
I made some simple plans, above, with the key dimensions. I know it's a bit rough and ready but I didn't see much point in carefully drawing out plans, at this stage, when the real planning is going on as I make the watch itself. The next iteration may be a bit neater!