Resolution and surface finish

I am milling a circlular pocket with a 1/2" 2 flute HSS. The sides
of the pocket don't have that great of a surface finish. My mill has
.0005" minimum step resolution. Can this be causing the vertical lines
or is it something else like vibration? Dull tool? Will a 4 flute give
a better side finish?
The thing is that the original Bridegeport series 1 (boss5) only had
.001" resolution