Patent ID: 7370702

Claim:
A mill for cutting a window in a well casing, comprising: a mill body adapted for mounting on a work string for rotation downhole in a well casing; a plurality of blades formed on said mill body; a row of primary cutting inserts mounted on each said blade; a row of secondary inserts mounted on each said blade behind said row of primary inserts relative to the direction of rotation of said mill; and a buffer section on said mill, said buffer section having an outer diameter substantially at the full diameter of said mill, said buffer section being positioned to protect at least one of said primary cutting inserts at substantially full gage from impact damage; wherein said primary cutting inserts are formed of a relatively harder material than said secondary inserts, and said secondary inserts are formed of a relatively more durable material than said primary inserts; wherein said buffer section comprises a substantially full mill diameter section of said mill body.