That's quite a project - anodising it!
Nice machining there, I don't think my lathe skills are up to it (gave my lathe to a friend). We could try though
Anodising isn't too difficult. The problem lies with the electrolyte - sulphuric acid which needs to be about 30%. However, I use another chemical that is a lot safer and just as good ( but I can't remember what it is at the moment!* ). Other than controlling the electric current, it's fairly easy.
The machining was dead easy. All I did was get some 15mm ( IIRC ) aluminium bar. I faced it off and centre drilled it and then drilled it out to 11mm. I then bored it out to ( again IIRC ) 11.04mm.
I then parted it off to length and put the bit that was to become the button to one side whilst I turned the last 20mm of the bar ( still in the chuck ) down to about 11mm.
I then superglued the button onto the end of the bar ( the bar now being a mandrel ). With the button glued to the bar, I faced off the end and did a very light cut along the side. The bar was the correct size so this light cut was only done to clean the surface.
I then formed the radius using a suitable tool.
With the button still in the lathe, I switched on at fairly high speed and polished it with buffing pads on a dremel coated with blue metal polishing compound. It polishes up very quickly like this ( both the dremel and lathe rotating! ).
Finally, a few seconds with the blowtorch destroyed the superglue and allowed me to separate the button from the mandrel. When it cooled, I fitted it to the car. The 11.04mm(?) boring gave me a very snug fit to the car. No glue required.
Final tip : when machining aluminium, use WD40 as a lubricant! It does a really good job and results in very smooth work.
* It's used to pH balance swimming pools.