This video from cutting tool supplier Sandvik Coromant suggests the ideal way for a milling cutter to enter material from the side. As the different animations show, if the tool “arcs” into the material along an arc that follows the same direction as the tool’s rotation, then the load on the cutting edge varies gradually. By contrast, if the arc is opposite the tool’s rotation, or if the path is straight, then the shock to the tool is more pronounced.
These animations portray the tool entering into the straight edge of a rectangular part. However, the same idea applies to a tool entering the material from within a hole—such as a milling tool for roughing a pocket that enters the material from within a pre-drilled hole.