Why Can’t Milling Picks Be Directly Used as Bullet Teeth in Pile Drilling?

What Is a Milling Pick?

A milling pick is a replaceable cutting tool installed on a milling drum, milling roller, or other rotary cutting equipment. It is used to cut, scrape, strip, and break materials such as asphalt, concrete, rock, and coal.

What Are Bullet Teeth in Pile Drilling?

Bullet Teeth in Pile Drilling are replaceable cutting components installed on foundation drilling tools such as drilling buckets, drilling augers and core barrels. They are primarily responsible for directly cutting into, shearing, crushing, and breaking soil or rock formations during pile drilling.

What Are the Core Differences Between Milling Picks and Bullet Teeth in Pile Drilling?

1. Cutting Method

Milling picks primarily use the tooth tip to continuously scrape and mill the material as the equipment moves.

For example, during pavement milling:

Milling drum rotates → Tooth tip contacts the pavement at high speed → Tooth tip penetrates the material → Material is scraped and broken → Milled material is discharged

Therefore, milling picks generally place greater emphasis on:

- High-frequency cutting

- Wear resistance

- Cutting-edge sharpness

- Suitability for continuous cutting

- Stability at high rotational speeds

By contrast, Bullet Teeth in Pile Drilling typically operate on rotary drilling rigs through a combination of rotation and axial down pressure to cut or break the formation.

For example, during rock and soil drilling:

Drill string rotates + axial pressure is applied → Cutting teeth penetrate the soil/rock → Shearing, crushing, and breaking → Cuttings enter the drilling bucket

Therefore, Bullet Teeth in Pile Drilling place greater emphasis on:

- Penetration capability

- Impact resistance

- Bending resistance

- Adaptability to different ground conditions

- Tooth holder strength

- Performance under high torque, low rotational speed, and heavy loads

2. Working Parameters

Comparison	Milling Picks	Bullet Teeth in Pile Drilling
Typical equipment	Road milling machines, mining equipment, etc.	Rotary drilling rigs, drilling buckets, core barrels, etc.
Main movement	High-speed rotation / continuous milling	Low-speed rotation + axial pressure
Main function	Milling and scraping	Cutting, crushing, and breaking
Load on individual tooth	Relatively lower but frequent	Generally much higher
Impact conditions	Depends on the application	Frequently present
Key considerations	Wear resistance and cutting efficiency	Strength, impact resistance, and penetration capability
Typical materials	Asphalt, concrete, rock, etc.	Soil, sand, gravel, weathered rock, hard rock, etc.

Milling and scraping Cutting, crushing, and breaking

In rotary pile drilling, in particular, the load acting on an individual cutting tooth can be extremely high. When drilling through gravel layers, strongly weathered rock, or even hard rock, the tooth tip may be subjected to axial force, tangential force, and impact loads simultaneously.

3. Tooth Design

Milling picks typically feature a relatively characteristic conical or bullet-shaped carbide tip. This design allows the tooth tip to continuously roll and cut into the material during high-speed operation.

By comparison, Bullet Teeth in Pile Drilling are available in a wider range of designs, including:

- Flat teeth

- Bullet teeth

- Rock cutting teeth

- Soil cutting teeth

Different tooth geometries are designed for different ground conditions.

For example:

- Soft soil and clay: The focus is on soil cutting and spoil removal, so the tooth geometry can be relatively sharp.

- Sand and gravel: The teeth need to balance cutting performance with impact resistance.

- Strongly weathered rock: Good wear resistance and impact resistance become more important.

- Hard rock: Greater emphasis is placed on the overall impact resistance of the carbide tip, tooth body, and tooth holder.

4. Tooth Holder System

With Bullet Teeth in Pile Drilling, it is important not to look at the tooth alone.

In practice, the cutting system typically consists of: Cutting tooth + Tooth holder + Welding/Fixing structure + Drilling tool body

Because rotary drilling rigs can generate very high torque and down pressure, even a highly wear-resistant tooth can fail if the tooth holder does not have sufficient strength. Potential problems include:

Cracking of the tooth holder

- Tooth loss

- Tooth holder wear

- Tooth jamming

- Damage to the drilling bucket body or base plate

Therefore, the design of pile drilling tools generally needs to consider the overall load distribution and interaction between the tooth tip, tooth holder, and drilling tool body.

5. Applications

Milling Picks: The Focus Is on “Milling Away”

Typical applications include:

- Asphalt pavement milling

- Concrete surface treatment

- Road surface rehabilitation

- Continuous mining

- Continuous cutting in tunnels and underground construction

- Certain rock milling applications

A key characteristic is that the material is already exposed in front of the equipment. The equipment primarily performs continuous cutting on the material surface or working face.

Bullet Teeth in Pile Drilling: The Focus Is on “Drilling Into”

Typical applications include:

- Building pile foundations

- Bridge foundations

- High-speed railway and railway bridge foundations

- Metro and underground construction

- Wind turbine foundations

- Port and marine infrastructure foundations

- Large-diameter bored piles

- Deep foundation engineering

6. “Final Goal”

Milling picks：Remove material from a surface or working face.

Bullet teeth in pile drilling：Cut and break the ground to create a borehole.