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 A revolutionary reverse actuation mechanism ensures and maintains full tool opening, while the drill string weight prohibits tool closure in a direct ratio of 1:1. A large piston area provides the hydraulic horsepower, which also functions to maintain full tool opening. To dose the underreamer, the drill string must be physically lifted off the bottom with the mud pumps shut down, thus allowing the cutter arms to collapse downward and into the body.

The patented cone is specifically designed for underreaming application. The rolling radius of these cones is consistent with undereaming diameters downhole, resulting in longer seal and bearing life.

A patented internal cage design doubles seal life and substantially reduces bearing wear. As the cone completes on revolution, the cage only rotates one half turn. Thus, the lives of both seals and bearings are substantially increased allowing for longer downhole times and a reduced number of trips.

 Because the cutter arms move upwards in the body, the hinge pins which attach them to the yoke are trapped within the arm slots. This feature makes it virtually impossible for hinge pins to vibrate lose, leaving cutter arms downhole. Without changing any internal parts, the Underreamer can be adjusted to any size within it's range in as little as 10 - 15 minutes on the rig floor.

An integral jet sub located neat the bottom of the underreamer enables cone washing via three or six replaceable jets. Effective and thorough washing means longer tool life, better penetration rates and fewer downhole trips. The technological advances inherent in the DTU Underreamer design have made it the strongest, most trouble-free and economical underreamer to ever hit the market.

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