Cutting edge solid state hard disk technology

Found an aluminum disk on marktplaats.nl, 20mm thick with a diameter of 235 mm, the right size for the top of my vacuum chamber.
Machining is easier with aluminum:

The surface was not really smooth, but it's a very solid and hard disk.
It took some maching to get the surface clean, I'm not there yet, but this is what it looks like now:

It will be on top of the fusor, with a viton ring between the aluminum cap and the stainless steel hemisphere.
Which brings us to our "cutting edge" technology.
The upper and the lower hemisphere have to be connected to the aluminum cap and the turbomolecular pump. But the edges were damaged, so I tried soft soldering, which was not a good idea (bakeout impossible). I tried heathing the hemisphere is a coal fire and then hard soldering with a torch. That didn't work, the temperature was too low.
Finally I just tried cutting the edge with the right angle grinder. First with a grinding wheel and after that with 2 different radial flap discs.
And it worked, this is the result:

The first time I also tried the whetstone, but that is not needed, grinding wheel, rough radial flap disc, smooth radial flap disc and then some polishing does it.
This is a first impression of the construction, imagine the turbo pump under the chamber: