Hole Openers and Underreamers (Section 8)

Hole Openers

The Mills Machine holeopener is used to enlarge or ream an existing pilot hole or can be run above a pilot bit to simultaneously drill and enlarge a hole. These rugged tools are built for the toughest drilling applications. The use of holeopeners has gone from an optional operation to standard practice for most drillers. The prime reasons for using holeopeners are economy, accuracy, speed, and flexibility of size. With over forty-five years of experience Mills Machine can design and manufacture the exact tool for your individual requirements. Fabricated Roller Cone ( see Rotary Holeopeners, in this catalog) Fixed Arm Roller Cone (see Rotary Holeopeners, in this catalog) Drag Bit, fixed and replaceable blade (see Rotary Drag Bit in this catalog) Claw Bit (see Rotary Claw Bit in this catalog) Holeopeners or Roller Back Reamers are available for Horizontal Road Boring or Horizontal Directional Drilling applications. Configurations include roller cone, drag (blade) type or claw (bullet) type in any size and with any connection. These rugged units are manufactured with a reverse pitch on the cutters for pulling back through the pilot hole. We also manufacture a line of Free Bore and Casing Push bits for the Horizontal road Boring market. Configurations include roller cone, drag (blade) type or claw (bullet) type in any size and with any hex connection. The Roller Cone type features a special Positive Cam Lock Design for pushing casing as you drill. This type of bit is made to cut very hard rock formations. Blade and Bullet configurations are offered with a flip out cutters for soft to medium formations.


Roller Cone and Drag Type Underreamers are just two more examples of our goal to bring expensive Oil Field technology to other drilling markets at an economical cost. We have been manufacturing both types of Underreamer designs for over twenty years and based on the feedback from our customers out in the field we have been able to offer continual improvements. The primary use for both of these tools is to open up the bore hole below the casing. Most drillers are trying to straighten up a dogleg down the hole, which may be preventing advancement of the casing. Other uses include opening up zones down the hole to increase the yield of a well or seal off salt water intrusion from the bottom of the hole. The construction industry has used underreamers for tie back or anchor holes in any type of dirt, rock or concrete formations. Our Underreamers can be opened up anywhere down the hole and as many times as needed but, you must have adequate annular space for the blades or rollers to open up. Most drillers pull the casing up 3 or 4 feet and lower the underreamer below the casing and then open the tool and start drilling. The tools operate with either air or fluid pressure and require as little as 60 – 100 lbs. of pressure to force the cutter arms out. The bodies and cutter arms are manufactured from heat treated steel. The piston is carbonized steel to reduce abrasion and features a replaceable tungsten carbide jet nozzle to adjust to your individual compressor or mud pump output. Additional circulation holes have been added into the side of the piston body to keep the cuttings out of the cutter slots. The simple, rugged design features easily replaced components for long term, trouble free operation. The operation of our Underreamers is very simple. The tool 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. When the pump pressure is shut off, a coil spring forces the piston upward causing the cutter arms to retract back into the body. We can custom manufacture an underreamer to meet your individual requirements.

Hole Openers and Underreamers