Consider helical interpolation over plunging to achieve better tool life, surface finishes and usually faster cycle times. Helical interpolation is producing a circular hole by having the carbide end mill describe a helical motion as it moves to down to the full depth. This greatly reduces cutting forces and chip flow of the end mill which leads to longer carbide end mill life and improved surface finishes. Consider a 5 to 10 degree angle for a conservative approach and if you want to be aggressive 10 to 20 degrees should speed up your cycle time.
14th Dec 2015