No need to apology Bony, there's no trouble at all, your remark was absolutely relevant, but I never miss an occasion to play with my tools and to give myself some challenges.
Here I did know this brass copler I had could fit, but it was not easy to predict the exact milling to be done with precise dimensions . Hence the 3d modelling, I could make some virtual cuts and see the intersection between the cylinder with the odd shape of the button.
It's just fun for me, I like doing this, and I was initially thinking of doing the complementary shape of the button with my small cnc, stacking layers of plywood I would have cut following the different sections of my drawing.
But at the end I had fun playing with my conventional mill and the rotary table.
But for sure, do not see any logic but trying to have fun with my tooling and finding solution to unprobable challenges I set to myself.