Need advise on aluminium cone/horn design, ideally from a lathe machinist.

[JOGARA]

You could go sub 1mm wall thickness, but 1mm should be thick enough to not have to worry too much about strength while machining.

What do you mean by round over? Just a radius on the end?
On a CNC the difference between square, chamfered, and rounded, is a line or two of code. The only problem would be if you wanted both ends radiused internally and externally, as you're then potentially into a second op.

Ah okay.
I probably wont go too thin but 1-2mm sounds good to me. This is going to be one of those things that gets knocked a lot so need some thickness I believe. Though obviously a round tube is stronger than a flat 1-2mm sheet...

Yea just a little radius to take the edge off.
A chamfer will be okay too. Just so the powder coat does not mess up on the ends.
Wont need it on the smaller end, that will get fitted to another part..