Eccentric Drill Bit

What is Eccentric Drill Bit?

An eccentric drill bit is a drilling tool where the cutting section is offset from the drill rod axis. It works in conjunction with a guiding mechanism to achieve efficient rock breaking and precise hole formation. The centrifugal and impact forces generated by its eccentric rotation easily break through hard rock layers, while also preventing problems such as borehole collapse and deviation. Its performance is superior to traditional concentric drill bits.

Our eccentric drill bits are forged from high-strength alloy steel, and the cutting teeth are made of wear-resistant cemented carbide. They undergo multiple heat treatments for enhanced strength and are suitable for complex geological conditions ranging from soft soil and sand layers to moderately weathered rock, increasing drilling speed and extending service life.

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Features and Advantages of Eccentric Drill Bit

Enables Casing Follow-Up Drilling

The eccentric structure expands the borehole diameter synchronously during drilling, creating sufficient space for casing to follow closely. This integrated operation ensures stable casing placement and avoids the risk of casing jamming caused by borehole shrinkage, which is crucial for efficient well completion.

Suitable for Complex Formations

It exhibits excellent adaptability in loose sand, gravel, fractured rock, and weathered rock formations. The eccentric cutting force strengthens the crushing of unstable formations, while the optimized chip removal channel reduces sediment accumulation, effectively enhancing borehole wall stability and preventing collapse.

High Construction Efficiency

It eliminates the tedious processes of repeated casing installation, drill bit retrieval, and re-drilling. The "drilling + casing following" one-stop operation reduces non-drilling time significantly, improving overall construction efficiency by 30% or more compared to traditional drilling methods.

Reusable with Excellent Economy

The eccentric wings are designed with flexible deployment and retraction mechanisms, which can withstand multiple cycles of expansion and contraction without performance degradation. The durable structure allows repeated use in different drilling projects, reducing the frequency of replacement and lowering overall procurement costs.

High Borehole Accuracy

The precise eccentric offset and integrated guidance system ensure consistent borehole diameter and smooth wellbore surface. The stable drilling trajectory avoids deviation, laying a solid foundation for subsequent well completion operations such as well pipe installation and water filtering layer setting.

Strong Wear Resistance & Long Service Life

The drill body is forged from high-strength alloy steel, and the cutting teeth adopt imported wear-resistant cemented carbide. Through multi-pass heat treatment, the surface hardness reaches HRC 58-62, enabling it to maintain stable cutting performance even after long-term operation in harsh geological conditions.

Parameter of Eccentric Drill Bit

Eccentric Drill Bit
Model	Casing Tube Size (mm)	Casing Shoe Size (mm)	Maximum Reaming Size (mm)	Impact Hammer Size (inch)
108 Eccentric Casing system	108	86	118	3
114 Eccentric Casing system	114	94	124	3
127 Eccentric Casing system	127	102	136	3~4
146 Eccentric Casing system	146	117	156	4
168 Eccentric Casing system	168	138	178	5
178 Eccentric Casing system	178	148	193	5
183 Eccentric Casing system	183	152	193	5
194 Eccentric Casing system	194	167	208	6
219 Eccentric Casing system	219	193	237	6～7
245 Eccentric Casing system	245	210	260	6~8
273 Eccentric Casing system	273	242	308	8
325 Eccentric Casing system	325	285	355	8～10
377 Eccentric Casing system	377	333	420	10～12

What is the Working Principle of Eccentric Drill Bit?

The working principle of eccentric drill bits is rooted in their unique structural design, which integrates “efficient rock breaking” and “synchronous borehole protection” to solve core pain points in water well drilling, such as borehole collapse and low construction efficiency. Below is a detailed breakdown of its operating process:

Eccentric Body Unfolds to Enlarge Borehole At the start of drilling, the drill string drives the eccentric drill bit to rotate at high speed. Under the action of centrifugal force generated by high-speed rotation, the eccentric wings (the core component of the drill bit) automatically unfold outward. This unfolding action makes the effective cutting diameter of the drill bit larger than the casing diameter, quickly forming a large-diameter borehole that provides sufficient space for subsequent casing lowering.

Synchronous Drilling & Casing Lowering Unlike traditional drilling methods that require separate drilling and casing installation, the eccentric drill bit enables “drilling while casing following”. As the drill bit continues to advance and break rock, the casing is smoothly lowered into the already enlarged borehole. This synchronous operation avoids the risk of borehole wall instability caused by delayed casing installation.

Eccentric Body Retracts for Easy Retrieval When the drilling reaches the preset depth, the drill string is reversed. The reverse rotation triggers the mechanical linkage structure inside the eccentric drill bit, making the expanded eccentric wings retract inward. After retraction, the overall diameter of the drill bit is reduced to be smaller than the inner diameter of the casing, allowing the drill bit to be easily pulled out of the casing without obstruction.

Casing Remains to Stabilize the Borehole After the drill bit is completely retrieved, the casing remains in the borehole as a permanent support structure. It effectively isolates the unstable formation from the wellbore, preventing borehole collapse, sediment influx, and well diameter shrinkage, thus ensuring the quality of the borehole and creating favorable conditions for subsequent water well development.

This integrated working principle not only simplifies the drilling process but also maximizes the synergy between the drill bit and casing, which is the key reason why eccentric drill bits are widely used in complex formation drilling.

Eccentric Drill Bit Operating Steps

First Step

When starting drilling, the reamer swings out and reams the pilot-hole wide enough for the casing tube to slide down behind the drill bit assembly.

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Second Step

When the required depth is reached, rotation is reversed carefully, whereupon the reamer swings in. Allowing the drill bit assembly to be pulled up through the casing.

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Third Step

Casing tubes that are to be left in the drill hole should be sealed at the bottom of the hole by means if cement grout or some other sealing agent.

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Fourth Step

Drilling continues to the desired depth in the bedrock using a conventional drill string.

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Main Components and Their Functions of Eccentric Drill Bit

Main Body: The core of the drill bit, used to withstand drill pressure, mount the eccentric body, and guide drilling. It typically has several carbide teeth or PDC teeth.

Eccentric Wing: The eccentrically deployed section, a key component for enlarging the borehole diameter. It deploys during operation to drill a larger hole and retracts to facilitate drill bit recovery.

Pivot Axis: Connects the eccentric body to the main body, allowing it to rotate freely between deployment and retraction.

Carbide Teeth: Distributed on the main cutting face and eccentric wings, directly cutting the rock; the core of rock breaking.

Pilot Face: Located at the center of the drill bit, controlling the drill bit’s direction and maintaining drilling stability.

Flushing Channel: Used to spray air or flushing fluid to cool the drill bit and remove rock cuttings, preventing borehole blockage.

Thread Connection: Connects to drill pipe or down-the-hole hammer to transmit torque and impact force. Common standards include API, DHD, and QL.

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FAQ of Eccentric Drill Bit

Should It Be Used With a Mud Pump Or An Air Compressor?

The eccentric drill bit needs to be used with an air compressor. The air compressor provides a high-pressure airflow to drive the down-the-hole hammer. During drilling, the eccentric block rotates to enlarge the hole, driving the casing to advance simultaneously with the drill string, achieving integrated drilling and casing installation. After reaching the target depth, the drill string is reversed, the eccentric block retracts, allowing the drill string to be smoothly withdrawn from the casing, completing the casing operation.

What Types Of Geological Formations Are Eccentric Drill Bits Primarily Suitable For?

Eccentric drill bits are primarily suitable for loose, fractured, and easily collapsing overburden formations, such as sand and gravel layers, clay layers, weathered rock layers, and gravel-bearing formations. Their core function is to enable casing advancement simultaneously with drilling, effectively preventing borehole collapse and drill string jamming. They are especially suitable for complex geological formations requiring borehole wall protection in projects such as water wells, anchoring, and pipe roofing.

What Are The Differences Between Eccentric Drill Bits And Concentric Drill Bits?

Eccentric drill bits have a larger hole diameter and are suitable for loose, easily collapsing formations, offering good borehole wall protection;
Concentric drill bits have a simpler structure, are less prone to jamming, and are suitable for more homogeneous, less prone to collapsing formations, but their hole-enlarging capacity is slightly weaker;
The actual selection should be based on a comprehensive consideration of formation stability, drilling efficiency, and cost.

What Precautions Should Be Taken When Drilling With An Eccentric Drill Bit?

Before drilling, check whether the eccentric block rotates smoothly and whether the ventilation is unobstructed;
Control the feed rate during drilling, reduce pressure in loose formations, and frequently clean the borehole;
Lift the drill string slightly every 0.3-0.4 meters to prevent the drill bit from getting stuck;
Avoid forcefully pulling up the drill string to prevent damage or jamming of the eccentric block.

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Eccentric Drill Bit

What is Eccentric Drill Bit?

Features and Advantages of Eccentric Drill Bit

Parameter of Eccentric Drill Bit

What is the Working Principle of Eccentric Drill Bit?

Eccentric Drill Bit Operating Steps

First Step

Second Step

Third Step

Fourth Step

Main Components and Their Functions of Eccentric Drill Bit

FAQ of Eccentric Drill Bit

Should It Be Used With a Mud Pump Or An Air Compressor?

What Types Of Geological Formations Are Eccentric Drill Bits Primarily Suitable For?

What Are The Differences Between Eccentric Drill Bits And Concentric Drill Bits?

What Precautions Should Be Taken When Drilling With An Eccentric Drill Bit?

Related product recommendations

Drill Rod

DTH Hammer

Impact Drill Bit

PDC Drill Bit

Mud Pump

Tricone Drill Bit

Your SatisfactionIs Our Successe

Your Satisfaction
Is Our Successe