Hi,

A few things about circles. Many times the number of polygons used to make the circle is low which results in a "circle" made up of obvious straight line segments. In OpenScad you can add a line in at the beginning of the design that will increase the polygons so that it is obviously a circular hole. That said, I've always had trouble getting my holes to measure correctly. I've actually given up and just make them big enough so that I can run a drill through them to make them the right size. I know, shouldn't have to do this, but it does make for a quick solution and it is so easy that I haven't bee tempted to tackle the problem again.