Information hub and thought leadership portal by Boart Longyear


julio 18, 2019

Overburden Casing Bits - Design, Materials, and Manufacturing

Z Design Casing Bits

Overburden drilling equipment and drill strings (including casing, rods, casing shoes, casing bits,  bits) along with a skilled driller are required for drilling straight and consistent boreholes through all overburden materials, fluctuating from very soft, broken ground to exceptionally hard, compact conditions. Drillers balance thrust, torque, rotary speed, flush parameters, and percussive force to penetrate the varying ground encountered.

Boart Longyear historically named their overburden and construction drilling products line for this type of drilling “Delta” tools. In addition to being the fourth letter of the Greek alphabet, and a code word representing the letter D, (used in radio communication), delta is also defined as the difference between two things or values, or the average change of any changeable quantity. In short, the overburden construction drilling product line was designed for drilling through changing ground conditions typically encountered above bedrock.

With more and more challenging and larger specialty geotechnical construction projects in difficult, complex, and varying ground conditions, rotary and percussive drill rigs in the construction industry were getting stronger and more powerful. Bigger, stronger, and more powerful rigs subsequently required larger, stronger, longer-lasting construction drilling tools – including better designed and manufactured casing bits.

Casing bits are used in deep, difficult overburden when a casing shoe is not sufficient to drill to depth. There have not been any significant advancements made in casing bit designs since the 1990’s. The so called “proven, bullet-proof” bits were made day after day without questioning the physical mechanics or what might be possible with a new or improved design.

In light of this, Boart Longyear decided to partner with its customers to look at redesigning casing bits in the geotechnical construction drilling field.

The first discovery in this initiative was that drilling site feedback often compared apples to oranges about bit designs and there was no real definition of drilling bit designs or any so-called standard. The sum of differing opinions needed more segmentation and analysis. After interviewing customers, experienced drillers, and engaging our internal engineers, all of the feedback was segmented and combined with proven manufacturing information and our new Z Design casing bits were created, tested, and are now available to the industry.

Combining the three main aspects in faster and longer lasting casing bits: cutting, flushing, and gauge protection, Z Design casing bits provide improved flushing, faster ROP (rate of penetration), and longer lasting bits. The difference is in the design and materials. Using premium tungsten carbides, high quality steel, improved gauge protection, and induction brazing to reduce blistering, Z Design casing bits are manufactured in our ISO-Certified, Eiterfeld, Germany manufacturing plant.


Casing bit bodies are constructed of high strength quenched and tempered steel. The high-quality tungsten carbide inserts are induction brazed into the steel bodies ensuring a secure fit without overheating issues associated with flame brazing. Strict machining control of the carbide seats prevents premature loss of carbide inserts.


Tungsten carbide gauge protection on casing bits prevents excessive wear on the outer diameter of the bit in abrasive ground conditions. Additionally, in unconsolidated conditions where the ground is caving in on the drill string, gauge protection assists in freeing the bit and casing by providing another cutting surface.


When required, Boart Longyear offers shrink fit installation of all hemispherical, ballistic, and two-step tungsten carbide inserts instead of the standard induction brazing. This very precise construction method is often utilized when drilling in extremely hard ground conditions and provides both increased button retention and longer overall life.


  • Computer controlled induction brazing of tungsten carbide inserts for superior process control and overheating prevention, common with flame brazing
  • High-grade body construction with quenched and tempered steels
  • Optional tungsten carbide gauge protection available for unconsolidated grounds and increased bit life in abrasive conditions
  • Specialized designs for unique drilling situations such as drilling through reinforced concrete and drilling without inner bits.

Better casing bits means better drilling outcomes and ultimately results in better ROI (return on investment). Casing bits are designed for rotary percussive or rotation only drilling based on the tungsten carbide inserts utilized as well as the geometry of the bit. Customized tools for unique drilling applications are also available upon request.

Contact your local Boart Longyear representative or distributor to order the best casing bits in the overburden drilling market. Still not convinced? Contact us for help designing and implementing a testing drilling program to prove using Boart Longyear casing bits have a higher ROI.

For part numbers, download the Boart Longyear Overburden and Construction Tooling catalog here.


Download the Soil Class Casing Bit Comparison Chart 


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James Burris


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