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Milling and Drilling Differences in CNC

Aug 28, 2023

In the realm of modern manufacturing, Computer Numerical Control (CNC) machining has revolutionized the way intricate parts are fabricated. Two fundamental processes in CNC machining are milling and drilling, each serving distinct purposes with unique characteristics. This article delves deeper into the nuances of CNC milling and CNC drilling, highlighting their differences, applications, tool selection, and advantages.


What is CNC Milling?



CNC milling is a precision machining process that employs rotary cutters to remove material from a workpiece, producing a desired shape. This subtractive manufacturing technique is widely used for creating complex parts with high precision and tight tolerances.

Milling machines utilize a multi-point cutting tool that rotates about an axis. At the same time, the workpiece is affixed to a platform that moves along multiple axes to achieve the desired dimensions.


Types of Milling Operations

Milling operations are classified into several types, each catering to specific outcomes. Some common types include:

● Face Milling.

● Peripheral Milling.

● End Milling.

● Slot Milling.

● Plunge Milling.


Uses of CNC Milling

CNC milling is a versatile machining process with applications across several industries:


● Aerospace: CNC milling is essential for creating intricate components used in aircraft and spacecraft, ensuring precision and reliability in critical parts.

● Automotive: The automotive industry relies on CNC milling to manufacture engine components, transmission parts, and complex molds for vehicle bodies.

● Medical: In the medical field, CNC milling is employed to fabricate medical implants, surgical instruments, and devices with intricate geometries for improved patient care.

● Electronics: CNC milling is vital in producing printed circuit boards (PCBs) and electronic components, enabling precise designs and reliable connections.

● Prototyping: Rapid prototyping benefits from CNC milling, allowing designers to quickly create accurate prototypes for testing and validation before mass production.

● Mold Making: CNC milling is utilized in creating molds for injection molding, die casting, and other manufacturing processes, ensuring high precision and reproducibility.

● Precision Parts: Industries requiring components with tight tolerances, such as watchmaking and optics, rely on CNC milling to achieve intricate shapes and precise dimensions.

● Custom Manufacturing: CNC milling caters to producing custom parts and one-off designs, meeting specific requirements without requiring extensive tooling changes.

● Architectural Models: Architects and designers use CNC milling to craft detailed architectural models and prototypes, showcasing intricate design features.

● Consumer Goods: The production of consumer goods, from appliances to electronics, benefits from CNC milling for creating aesthetically pleasing and functional components.

● Jewelry Making: In the jewelry industry, CNC milling helps produce intricate and detailed jewelry pieces with precision and fine craftsmanship.


What is CNC Drilling?



CNC drilling, on the other hand, is a machining process that involves creating cylindrical holes in a workpiece using a rotating drill bit. Unlike milling, drilling is a single-point cutting operation that focuses on creating holes of precise diameter and depth. The workpiece remains stationary while the drill bit is brought into contact, penetrating the material to create holes.


Types of Drilling Techniques

Drilling techniques can be categorized based on the method and purpose. Some drilling types include:

● Twist Drilling.

● Gun Drilling.

● Counterboring.

● Countersinking.


Uses of CNC Drilling

CNC drilling plays a pivotal role in various industries where precision holes are essential:


● Printed Circuit Boards (PCBs): In electronics manufacturing, CNC drilling creates the holes required for components and connections on PCBs, ensuring accurate alignment and reliable electrical connections.

● Aerospace Components: The aerospace industry relies on CNC drilling to produce holes in components like turbine blades, aircraft frames, and structural parts to exact specifications for safety and performance.

● Mechanical Assemblies: Mechanical systems and assemblies require precisely drilled holes for proper alignment, fitment, and functionality, making CNC drilling indispensable.

● Automotive Manufacturing: CNC drilling is used in the automotive sector to create holes for bolts, fasteners, and various components, ensuring structural integrity and safety.

● Oil and Gas Industry: In oil wells, CNC drilling is crucial for creating precise holes in well casings and equipment, facilitating resource extraction and well maintenance.

● Medical Devices: Medical equipment and devices require accurately drilled holes for features like tubing pathways, connectors, and mounting points, ensuring proper functionality.

● Construction: In construction, CNC drilling is utilized for creating holes in building materials like concrete, steel, and wood, aiding in structural integrity and utility installation.

● Jewelry Making: Precision holes are essential in jewelry fabrication for inserting gemstones, creating clasps, and adding intricate designs to various jewelry pieces.

● Manufacturing Processes: CNC drilling is a critical step in many manufacturing processes, including stamping, forging, and extrusion, where accurately drilled holes enable efficient operations.

● Electrical Installations: CNC drilling creates holes for conduits, wires, and electrical components in commercial and residential installations.

● Plumbing and Pipelines: In plumbing and pipeline systems, CNC drilling is essential for creating holes in pipes, fittings, and fixtures for proper fluid flow and connections.


The Difference Between CNC Milling and CNC Drilling




One of the primary distinctions between CNC milling and drilling lies in their flexibility. Milling is highly versatile and capable of producing various shapes and features on a workpiece. It can perform operations like face milling, contouring, and threading.

This versatility stems from the multi-axis movements of milling machines that allow for intricate patterns to be realized. In contrast, drilling is specialized for creating holes and lacks the versatility of milling regarding the variety of operations it can execute.



CNC Milling

CNC Drilling


Versatile; various shapes and features

Specialized; primarily for holes


Face milling, contouring, threading

Hole creation


Chips Removal

During machining, the removal of chips or swarf is a critical consideration. In milling, chips are generated as the cutting tool engages with the workpiece, and effective chip evacuation is necessary to prevent tool damage and surface defects. Milling machines often employ chip conveyors and coolant systems to facilitate chip removal.

In drilling, chips are typically produced as coils, making their removal comparatively less complex. The spiral or helical nature of chips produced during drilling aids in evacuation from the hole.



CNC Milling

CNC Drilling

Chips Removal

More complex due to diverse operations

Comparatively simpler



Milling and drilling operations are conducted using distinct machines. CNC milling machines have multi-axis capabilities that enable intricate workpiece movements, allowing for complex geometries. These machines come in various configurations, such as vertical and horizontal milling.

Vertical milling machines are well-suited for applications that require end milling and face milling operations, while horizontal milling machines are ideal for heavy cutting tasks and multiple-side milling operations. On the other hand, CNC drilling machines are designed specifically for hole creation and lack the multi-axis movements of milling machines.



CNC Milling Machines

CNC Drilling Machines

Machine Type

Vertical, horizontal, multi-axis

Primarily designed for drilling


Multi-axis movements for complex shapes

Limited movement for hole creation


Motion Path of Cutting Operation

The motion path of the cutting operation differs significantly between milling and drilling. In milling, the cutting tool rotates about its axis while simultaneously moving along multiple axes to shape the workpiece. This results in intricate patterns and shapes being carved into the material. Their multi-axis configuration enables the complex, fluid movements of milling machines.

On the other hand, drilling involves a straightforward axial motion of the drill bit into the workpiece to create holes. This axial motion is comparatively simpler and is sufficient for hole-making operations.



CNC Milling

CNC Drilling

Motion Path

Complex multi-axis for shaping

Axial motion for hole creation


Position of the Workpiece

The orientation of the workpiece also sets milling and drilling apart. Milling machines can hold the workpiece at various angles, facilitating the creation of inclined surfaces and intricate contours. This capability is particularly useful for applications where complex three-dimensional geometries are required.

The multi-axis movements of milling machines enable the tool to approach the workpiece from various angles, giving rise to diverse shapes. In drilling, the workpiece is usually held in a fixed position, allowing for consistent hole creation. The stationary workpiece simplifies the setup process and ensures consistent hole placement.



CNC Milling

CNC Drilling


Various angles for complex shapes

Fixed position for hole creation


Tool Selection for CNC Milling and CNC Drilling


The selection of cutting tools for CNC milling and CNC drilling is critical to achieving precise and efficient machining operations. These tools determine the final product's quality and the manufacturing process's overall effectiveness.

In this context, understanding the distinctions between various tool types is essential. Two primary categories of cutting tools, each with distinct characteristics and applications, are double and multi-point. This table provides an overview of these tool types, shedding light on their features and the operations for which they are best suited.


Tool Type






Double Point Cutting Tool



- Has two cutting edges

- Primarily used for drilling operations

- Engages both cutting edges to remove material from the workpiece.

- Creates holes with precision.

- Some tools with more than two cutting edges can also be used for drilling operations.




Multi-Point Cutting Tool



- Has more than two cutting edges.

- Used for milling operations.

- Multiple cutting edges remove material from the workpiece.

- Shapes and contours the


- Includes tools like Endmills and milling cutters.

- Suitable for complex geometries.


The selection of cutting tools for CNC milling and drilling depends on the specific machining tasks and materials involved. Here's a breakdown of tool selection for each process:


Tool Selection for CNC Milling

CNC milling encompasses a variety of operations, each requiring specific tooling. Multi-point cutting tools are commonly used for milling tasks due to their versatility and ability to shape intricate features:

● Endmills: Endmills are versatile tools with cutting edges at the bottom and sides. They are used for tasks like profile milling, slotting, and contouring, and are available in various shapes and sizes for different applications.

● Face Mills: Face mills have cutting edges on the face of the tool. They excel at producing flat surfaces and are often used for facing operations and shallow pocket milling.

● Ball Nose Cutters: Ball nose cutters have a rounded tip and are used to create curved surfaces, 3D contouring, and sculpt complex shapes.

● Shell Mills: Shell mills have cutting edges on the periphery and are suitable for larger cutting depths and heavier machining tasks.


Tool Selection for CNC Drilling:

CNC drilling primarily focuses on creating holes with precision. Different drill bits are used to achieve specific hole characteristics:

● Twist Drills: Twist drills are the most common type of drill bits, featuring spiral flutes for chip evacuation. They come in various sizes and point angles for different materials and hole diameters.

● Center Drills: Center drills create precise center holes that act as starting points for subsequent drilling operations, ensuring accurate hole placement.

● Spot Drills: Spot drills create shallow indentations on the workpiece to guide the drill bit, enhancing accuracy in hole placement.

● Indexable Drill Heads: Indexable drill heads are used for larger hole diameters and drilling depths. They consist of replaceable inserts, allowing for cost-effective maintenance.

● Gun Drills: Gun drills are specialized tools for deep hole drilling, often used in industries like automotive and aerospace for creating deep and precise holes.


The choice of tool depends on factors such as material type, hole diameter, hole depth, required surface finish, and machining speed. CNC operators consider these factors to select the most appropriate tool for achieving the desired machining outcome in accuracy, efficiency, and quality.


Pros and Cons of CNC Milling and Drilling

Here are the advantages and disadvantages of employing both of these operations:


CNC Milling


● Versatility and Complex Shape Cutting: CNC milling offers the advantage of efficiently cutting intricate and complex shapes with precision due to its multi-axis movement capability.

● Repeatability and Batch Production: CNC milling allows for producing multiple identical parts from a single design, ensuring excellent repeatability in mass production.

● Labor and Productivity Efficiency: Being computer numerically controlled, CNC milling reduces labor costs and enhances productivity by automating machining processes.



● High Initial Investment: The expense of acquiring and setting up CNC milling machinery is considerable, making it a substantial upfront investment.

● Skill Requirement: Operating CNC milling machines demands highly trained personnel due to their complexity, adding to operational costs.

● Repair and Downtime Costs: In case of breakdowns, repairing CNC milling machines can be expensive and time-consuming, affecting production schedules.


CNC Drilling


● Precision and Repetition: CNC drilling offers exceptional accuracy and repeatability in creating holes, ensuring consistent quality across multiple parts.

● Speed and Precision in Complex Structures: It excels in drilling holes rapidly and with utmost precision, even in intricate structures, thereby boosting productivity.

● Suitability for Low-Volume Production: Due to its lightweight design and efficient hole-making capabilities, CNC drilling is advantageous for low-volume production scenarios.



● Complex Repair and Maintenance: Repairing and maintaining CNC drilling equipment can be intricate and costly, impacting overall operational expenses.

● Limited Cutting Motion: The cutting motion of CNC drilling is primarily focused on hole creation, limiting its application to tasks beyond hole-making operations.

● Lack of Versatility: Cannot create complex shapes or contours.




In the world of CNC machining, both milling and drilling are indispensable techniques, each serving specific purposes. While milling excels in shaping and intricate detailing, drilling is vital for creating holes. Understanding their differences and applications empowers manufacturers to choose the right technique for optimal results.



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