Drilling apparatus

The apparatus of any of the preceding claims, wherein cutting portions of each blade extend across the full width of the blade in a direction parallel to the pivot axis or axes of the blades.

The apparatus of any of the preceding claims, wherein the maximum gauge cutting portions comprise part-cylindrical cutting areas.

The apparatus of any of the preceding claims, wherein, with the blades in the retracted position, the retracted position gauge cutting portions define part-cylindrical cutting areas.

The apparatus of any of the preceding claims, wherein, with the blades in the extended position, the retracted position cutting portions provide cutting areas adapted for back-reaming.

The apparatus of any of the preceding claims, further comprising means for locking the blades in a selected position.

The apparatus of any of the preceding claims, further comprising means for mechanically locking the blades in a selected position.

The apparatus of any of the preceding claims, further comprising means for locking the blades in the extended position.

The apparatus of any of the preceding claims, further comprising means for mechanically locking the blades in the extended position.

The apparatus of any of the preceding claims, wherein the retracted position gauge cutting portions are adapted to facilitate extension of the blades by allowing the cutting of an increasing diameter bore to accommodate blade extension.

The apparatus of any of the preceding claims, wherein the cutting blades each define a cutting portion which, with the blades fully extended, defines a forward facing cutting face.

The apparatus of any of the preceding claims, wherein, with the blades fully extended, each gauge cutting portion presents a cutting area in an axial plane.

The apparatus of any of the preceding claims, wherein the body has a leading end defining a cutting area.

The apparatus of any of the preceding claims, wherein the blades are pivotable on a common axis.

The apparatus of any of the preceding claims, further comprising a blade actuation arrangement.

The apparatus of any of the preceding claims, wherein the body defines one or more fluid passages which direct fluid onto or towards the blades.

The apparatus of any of the preceding claims, wherein the body includes at least one body passage which is only opened when the blades are at least partially extended.

The apparatus of any of the preceding claims, wherein the body includes a body passage which is progressively opened as the blades are extended.

The apparatus of any of the preceding claims, wherein the body includes a plurality of body passages which open in sequence as the blades are extended.

The apparatus of any of the preceding claims, wherein the body includes at least one body passage which directs fluid to an area of the apparatus for cleaning or purging purposes.

The apparatus of any of the preceding claims, wherein cutting portions or areas of the blades and body are provided with cutting elements.

Drilling apparatus comprising:

• a body;
• and
• at least two cutting blades pivotally mounted to the body and movable between a retracted position and an extended position, each cutting blade having a retracted position minimum gauge cutting portion and an extended position maximum gauge cutting portion.

Downhole drilling apparatus comprising:

• a body defining a diameter;
• and
• at least two cutting blades pivotally mounted to the body and movable between a retracted position and an extended position, the blades being adapted to cut in both the retracted and the extended positions and in the retracted position the blades describing a swept diameter larger than said body diameter.