Top cap

Working on the top cap this weekend, the surface of the aluminum was quite rough, but armed with new sandpaper wheels for my right angle grinder and some heavy polishing it now has a mirror-like surface.
I have put some petroleum jelly on it right after polishing, to prevent oxidation for now.
Next time I will clean of the jelly and give it a potassium hydroxide bath, when the surface will be exposed to air after washing off the potassium hydroxide, it will form a thin dense layer of Al2O3, without the hydroxide it would form a thicker, more open layer of aluminum oxide.
Also made some clamps for the top cap:

Also got the viton o-rings last Friday, from Polymax, prompt delivery and good prices.
The o-rings are shore 75, I would have preferred shore 90 (the force will be high on the big rings) from Eriks, but their web-shop did not show any prices, and they asked extra money for orders lower than 350 euro's!
I would like to construct a double ring system where the space between the rings is connected to pre vacuum, a construction like that can prevent leakage caused by the permeability of the rings. But that's the next step.
There is a lot of machining to do....