A plunge point will be ignored if it results in a gouge to the part. You will see a warning in your Operations sheet when the program ignores a plunge point. For example if you specify a plunge point that is closer to a wall than the tool radius, then the plunge point will be ignored. There is also a more subtle variation of this rule that may come into play: if the user's chosen plunge point gouges on its way to the starting point of the toolpath, then here too the plunge point will be ignored. In order to understand this see Using plunge points to control the start point of a finish milling pass. .