Patent ID: 7575070

Claim:
A downhole abrading tool for rotatably abrading an object in a well, the downhole abrading tool comprising: a body for connection to a drill string and having a drilling fluid passageway therethrough with an outlet for the passage of a drilling fluid having a drilling fluid pressure; a cutting end on the body for rotation against the object in the well; a chamber having a wear-away portion that is recessed within the cutting end, the wear-away portion wearing away and exposing the chamber to a wellbore pressure when the cutting end wears a selected amount; and a movable restrictor in fluid communication with the chamber and the drilling fluid passageway and, for movement from a first position to a second position, creating a pressure increase in the drilling fluid passageway when the chamber is exposed to the wellbore pressure; a partition disposed within the drilling fluid passageway; a sleeve disposed on an exterior surface of the body, the sleeve and the body defining an annular cavity, the restrictor being disposed within the cavity and the chamber being in fluid communication with a lower end of the restrictor; an upper port in the body above the partition leading from the drilling fluid passageway to the cavity; and a lower port in the body below the partition leading from the drilling fluid passageway to the cavity, wherein, while in the first position, the restrictor allows unrestricted flow of drilling fluid from the drilling fluid passageway, through the upper port and the lower port to the outlet and, in the second position, the restrictor at least partially blocks the lower port.