Only the 2 Axis Contour and the 3 Axis Z Finish operations use this Clearance parameter.. The parameter is only active when the Plunge Type is set to Ramp or Helical.
A horizontal plunge move is added to the end of a Ramp or Helical plunge move. The tool is kept away from the part contour by the additional plunge move. The Clearance parameter is the length of the additional plunge move. This value (labeled "d" in the following illustration) is the distance between the end of a Ramp or Helix plunge move and the first cut move. This examples shows a Ramp plunge move.