Downhole tool with extendable members

A downhole cutting tool for mounting between first and second sections of a drill string, the tool comprising:

• a mandrel for coupling to a first section of drill string;
• a body axially movably mounted on the mandrel and for coupling to a second section of drill string whereby application of weight to the string induces axial movement of the body relative to the mandrel;
• fluid pressure responsive means for moving the body axially relative to the mandrel on application of a fluid pressure force between the body and mandrel;
• and
• a radially extendable cutter mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induces radial movement of the cutter, the mandrel including means for drawing the cutter inwardly to permit positive retraction of the cutter from an extended configuration.

A downhole cutting tool for mounting on a drill string, the tool comprising:

• a mandrel;
• a body axially movably mounted on the mandrel;
• and
• at least one radially extendable cutter mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induces radial movement of the cutter, application of axial tension to the tool producing axial movement of the body relative to the mandrel tending to retract the cutter from an extended configuration,
• wherein the mandrel and body define a throughbore to permit drilling fluid to pass therethrough, a conduit extends from the throughbore to permit fluid to be directed towards the cutter and wherein the conduit is initially closed and is opened by relative movement of the mandrel and body resulting in extension of the cutter.

A downhole cutting tool for mounting on a drill string, the tool comprising:

• a mandrel;
• a body axially movably mounted on the mandrel;
• and
• at least one radially extendable cutter mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induces radial movement of the cutter, application of axial tension to the tool producing axial movement of the body relative to the mandrel tending to retract the cutter from an extended configuration,
• wherein the mandrel and body are rotatably coupled, the coupling permitting axial movement therebetween, and wherein the coupling is formed of co-operating hexagonal parts.

A downhole cutting tool for mounting on a drill string, the tool comprising:

• a mandrel;
• a body axially movably mounted on the mandrel;
• and
• at least one radially extendable cutter mounted in the body and being operatively associated with the mandrel such that relative axial movement of the mandrel and body induces radial movement of the cutter, application of axial tension to the tool producing axial movement of the body relative to the mandrel tending to retract the cutter from an extended configuration,
• wherein the mandrel and body are initially releasably fixed relative to one another to permit manipulation of the string without activation of the tool.