Roller Cone Underreamers



These are custom orderd to customer specs.  Please fill out and submit our Roller Cone Underreamer Application Questionnaire

Mills Machine Company has been manufacturing and continually improving the design of its Roller Cone Underreamer for over twenty years. The design is simple, yet rugged enough to provide the most efficient operation for opening up a hole. Through the use of highly efficient rock bit cones on the cutting arms, the tool is exceptionally fast in opening up a hole. The primary uses for this type of tool is to provide clearance for running casing, to obtain adequate annular space for cementing, or to enlarge zones for gravel pack completion. Recommended for soft to hard rock formations. The Mills Machine Roller Cone Underreamer:

  • Enlarges the borehole below the casing.
  • Produces positive cutter arm opening by direct pump pressure.
  • Rubber piston cup is designed for fluid or air drilling.
  • Features simple, rugged construction with a minimum of parts to ensure trouble-free operation.
  • Has adjustable carbide jet orifices to match output from your pump or compressor.
  • Features additional circulation holes drilled into the piston body to keep cuttings out of the cutter slots.
  • Sizes for 6″ casing and larger with Steel Tooth or TCI Button Cutters. -Any thread type, breakout flats, or float valve bore available.
  • The Mills Machine Underreamer is hydraulically operated by pump pressure which forces a spring loaded actuating piston downward. A cam attached to the lower end of the actuating piston forces the cutter arms out to the desired cutting diameter.

Adequate annular space is required to open the blades. When the pump pressure is shut off, a coil spring forces the piston upward causing the cutter arms to retract back into the body. The tool can be opened up anywhere down enabling you to open up as many zones as you like. To maintain your Mills underreamer simply clean and lubricate after each use and store in a dry area. Spare parts kits are available with the original purchase of your underreamer and for field repair of tool.