Have you looked at your GCode in the program.
If you are cutting a circle, then the correct GCode command is G2 to cut clockwise, G3 to cut counter clockwise. This is a single code for the whole of the arc or circle, and it either specifies a radius (with an R command) or specifies the centre of a circle (with an I,J, or K command) Mach 3 understands these two commands and adjusts the speed of both axis smoothly and simultaneaously to produce a circle.
The only way you can get "choppy" circles is if your Coral Draw or Lazy cam is not producing a circle when you draw, but is making up what appears to be a circle from lots of little, straight lines - a G1 code.
If you are using Constant Velocity, then this will smooth out a lot of the changes, until the straight lines get too long, and then you will get a threepenny bit effect or a fifty pence effect (a multi sided round coin with smooth edges).
You GCode will tell you which this is. The post Chip has highlighted is identical to your query and comes up with the same reply - although I don't think it resolved it.