Drag Type Underreamers



Drag Type Underreamers are custom ordered to customers spec’s.  Please fill out and submit our Drag Underreamer Application Questionnaire

Mills Machine Company has been manufacturing and continually improving the design of its Drag Type (Blade) Underreamer for over twenty years. The design is simple, yet rugged enough to provide the most efficient operation for opening up a soft to medium formation hole. Through the use of highly efficient tungsten carbide tipped alloy steel blades, the tool is exceptionally fast in opening up a hole below the casing. The primary uses for this type of tool is to provide clearance for running casing, to obtain adequate annular space for cementing, to enlarge zones for gravel pack completion or tie back anchor holes. Recommended for use in sand, dirt, clay, sand rock, sandstone, and hard shale formations. The Mills Machine Drag Type (Blade) Underreamer:

  • Enlarges the borehole below the casing.
  • Produces positive cutter blade opening by direct pump pressure.
  • Several blade designs are available for soft to hard formations.
  • 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 4″ casing and larger with tungsten carbide inserts or crushed carbide chips.
  • 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 milled opening in the side of the piston forces the cutter blades 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 blades 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.