How round are your milled parts?

Group,

Just out of curiousity, how round will your mill cut parts?

I was making some flat plates, 1/8" thick, 6061-T6 aluminum.
Different diameters, about 6" to 8.5". Using a .010" finish pass
with a 3/8" diameter end mill, I'm getting from .0005 to .0012" out-
of-roundness. Well within the customers tolerance of .002"+/- on
diameter.

My curiousity is aimed more at factory made CNC's or retrofits of
factory machines, especially newer machines. For instance, how
accurate are the new, low cost knee mills as they come from the
factory?

I know most home-brew setups can't be expected to hold close
tolerances so I'm not particularily interested in those. But, it'd
be interesting to hear stories if you have one that is very accurate.

BTW, I'm not asking how to tune my mill so it will make more accurate
circles. I know how to do that, it just isn't worth the effort on
this 10 year old machine.

thanks,

Doug