As it is with any type of interpolated curve editing, it may be a challenge to get control of the surfaces to hammer in the forms that you want, and this is especially true of anything that needs to be a perfect circle within the face of an object. There is a simple way and enter Devin Sloan with a quick little demonstration of how you are able to create a perfect circle shape when using HyperNURBS in Cinema 4d, extending the premise to create a hole using this nifty trick.
Quick little tutorial showing a technique for making perfect circles
Using some simple techniques on a 3D cube and making some simple cuts with the Cinema 4D Loop Tool and dividing up the cube into divisions, and then manipulating the new additions into a circle shape onto the surface of the cube by cleverly using a bevel that essentially generates an extrusion on the center point giving you circular edges on the cubes face.