by Sam Brown
CNC milling has become a cornerstone of modern manufacturing. It plays a crucial role in producing precision components for industries like aerospace, medical, and defence. If you’re sourcing parts that need to be exact, fast, and reliable, this is a process worth knowing.
You’ll discover what the CNC milling process involves, how different machines and operations are used, and what steps are needed to get started. The process offers a high level of precision, flexibility, and repeatability across a wide range of materials. Whether you’re working on a new design or managing production runs, understanding this process can help you make more informed decisions.
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Understanding CNC Milling
CNC milling is a process that uses computer-controlled machines to cut and shape materials into custom parts. It works like an automated carving tool that follows a digital set of instructions. If you’ve ever wondered what is CNC milling, it’s the process that transforms digital designs into physical components with precision.
This process works with a wide range of materials, including aluminium, stainless steel, engineering plastics, and composites. The CNC milling process is trusted in industries such as aerospace, medical, defence, and general manufacturing. Whether you’re prototyping or producing at scale, it delivers reliable, high-quality results every time.
Unlike CNC turning, where the part rotates and the tool stays still, the machining milling process keeps the material fixed while the cutting tool moves. This movement allows the tool to approach the part from multiple directions to achieve complex shapes. The metal milling process is ideal for parts that demand high precision and a clean, accurate finish.
Key Stages of the CNC Milling Process
Every CNC milling process starts with a 3D digital model created using CAD (Computer-Aided Design) software. This design includes all the necessary dimensions, geometries, and features of your part. CAM (Computer-Aided Manufacturing) software then converts the model into a set of instructions known as G-code.
These instructions tell the machine how to move, what speeds to use, and when to change tools. The raw material is secured in place, and the machine begins cutting based on the program. After machining, parts are inspected and may be finished with processes like deburring, anodising, or coating.
Types of CNC Milling Machines
CNC milling machines vary in design, and each type brings different capabilities to the table. The orientation of the spindle and the number of axes determine what kind of parts can be produced. Choosing the right setup impacts efficiency, complexity, and cost.
Vertical Milling Machines (VMCs)
A vertical milling machine features a spindle that moves up and down, aligned vertically. These machines are ideal for surface milling, slotting, and drilling simple features. VMCs are especially popular in prototyping and low-to-mid volume production runs.
They are easier to operate and program compared to more complex machines. Flat or easily accessible surfaces are ideal for VMCs, which makes them versatile for many jobs. Many workshops rely on them to provide precision cnc milling services with consistent output.
Horizontal Milling Machines (HMCs)
Horizontal milling machines have a spindle that is mounted horizontally, allowing side-to-side cutting. They are designed to handle deeper cuts, bulk material removal, and multi-face operations. HMCs are often used in production environments where speed and repeatability are critical.
The horizontal setup improves chip clearance, which helps with tool life and surface quality. Common applications include engine blocks, structural housings, and gearbox components. HMCs are an efficient choice for teams seeking complete cnc machining solutions.
Multi-Axis Milling Machines
Multi-axis milling machines move along more than the standard X, Y, and Z axes, offering greater flexibility. These machines can tilt and rotate parts, allowing access to more surfaces in a single setup. They’re commonly used in industries that require complex geometries and tight tolerances.
4-axis and 5-axis machines are the most common configurations in this category. These reduce manual setups, improve part accuracy, and shorten lead times. If you’re looking for cnc prototype machining expertise, multi-axis capabilities are often essential.
Common CNC Milling Operations
CNC mills can perform a wide range of operations depending on the toolpath and part design. Each technique serves a specific role in the machining milling process and contributes to the final part geometry. Knowing these operations helps you plan parts more efficiently and avoid costly rework.
Face Milling
Face milling is used to create flat, level surfaces on the top of a workpiece. A broad cutter removes a thin layer of material to produce a clean finish. This is often the first step in the metal milling process to prepare the material.
The result is a smooth, even surface that serves as a base for other features. Face milling is commonly used on enclosures, plates, and structural parts. It also helps square off raw stock for better accuracy in subsequent operations.
Peripheral Milling
Peripheral milling, also known as plain milling, removes material along the side of the cutting tool. It’s typically used to machine vertical edges, shoulders, and external profiles. This method supports consistent material removal along longer surfaces.
It’s a key part of the process when defining the outer geometry of a part. Peripheral milling is often used for brackets, covers, and rectangular components. It’s most effective for straight-edged, prismatic designs.
Slotting
Slotting creates grooves, channels, or keyways within the workpiece. A narrow cutting tool is used to cut straight through or partially into the material. These slots can help in alignment, fastening, or weight reduction.
Precision is critical to ensure correct fit and functionality in the final assembly. Slotting is especially common in aerospace, defence, and mechanical components. It’s a versatile operation in the milling metal process.
Drilling
Drilling produces cylindrical holes for fasteners, alignment pins, or clearance features. CNC machines use rotary cutting tools with programmed depth and diameter control. It’s one of the most frequently used operations in the CNC milling process.
This method allows for accurate and repeatable hole placement across multiple parts. Multi-axis setups can also create angled or off-centre holes without extra fixturing. Drilling is used in every industry, from electronics to medical devices.
Tapping
Tapping adds internal threads to a pre-drilled hole so it can accept screws or bolts. The tool follows a programmed pitch to form the threads consistently. It is usually performed directly after a drilling cycle.
CNC tapping eliminates thread variation and reduces manual labour. This operation is essential in parts that need fasteners for assembly or function. When combined with drilling, it improves efficiency in the overall machining milling process.
Materials Used in CNC Milling
CNC milling supports a wide variety of materials, allowing you to match your part's needs with the right material properties. Your choice will depend on functionality, appearance, durability, and overall cost. Below are the three most common categories used in the milling process.
Metals
Metals such as aluminium, stainless steel, and titanium are widely used in milling. These materials offer strength, stability, and excellent performance in high-stress environments. You’ll find them in critical applications across aerospace, automotive, and defence.
Aluminium is lightweight, corrosion-resistant, and machines quickly, making it ideal for fast-turnaround aluminium milling projects. Stainless steel is stronger and offers great wear resistance, often used in structural and medical parts. Titanium combines strength with low weight, perfect for demanding, high-performance components.
Plastics
Plastics are commonly chosen when weight, chemical resistance, or electrical insulation are priorities. Popular options include acetal (POM), PTFE, and nylon, all of which offer different mechanical properties. These materials are used in industries like electronics, food processing, and medical devices.
Plastic materials cut faster than metals, but require careful speed and tooling control to avoid melting. Using sharp tools and lower cutting speeds helps maintain part integrity. CNC milling produces smooth finishes and tight tolerances, even on softer materials like plastic.
Composites
Composites are engineered materials made by combining fibres with a matrix for enhanced performance. Carbon fibre-reinforced polymers (CFRPs) are the most common, known for their strength and lightweight profile. These materials are perfect for aerospace, defence, and high-performance automotive parts.
They are abrasive to machines, which makes tool selection and dust control critical during processing. Specialised tooling and vacuum systems are often needed to ensure a clean, safe cut. Despite the added complexity, composites deliver unmatched performance in weight-sensitive and structurally demanding designs.
Advantages of CNC Milling
CNC milling gives you accuracy, repeatability, and speed. It’s a reliable way to get custom parts made right the first time. Here’s why manufacturers across sectors use it every day:
- Consistent results from one part to the next
- Complex shapes with tight tolerances
- Compatibility with many materials
- Faster prototyping and production
- Fewer manual errors and rework
- Excellent surface finishes
- Safe, enclosed workspaces
- Efficient scaling from one part to thousands
- Trusted for quality in aerospace, medical, and defence
Steps to Begin CNC Milling
The first step in the CNC milling process is creating a 3D CAD model of your part. It’s important to design with machining in mind, avoiding undercuts, overly tight corners, or features that are hard to access. A trusted supplier can offer advice on manufacturability and help optimise your design.
Once the design is finalised, it’s converted into machine-readable code using CAM software. This code controls the tool paths, cutting speeds, and sequence of operations. After programming, the machine is set up, the material is loaded, and the part is milled, followed by inspection and any finishing steps required.
Mastering CNC Milling for Precision Manufacturing
CNC milling is about more than cutting; it’s about producing perfect parts, quickly and reliably. Whether it's a bracket for a jet engine or a medical implant with no margin for error, this process delivers precision where it matters most. That’s why it’s a preferred method in industries that demand tight tolerances and consistent quality.
At Penta Precision, we deliver that reliability through our ISO 9001:2015 accredited systems and engineering expertise. Our collaborative approach ensures every stage, from design to delivery, is aligned with your goals. With our precision CNC milling services, you gain a trusted partner who’s focused on reducing delays, improving outcomes, and keeping your supply chain running smoothly.