CNC Machining Guide

Step 1: Create a 3D CAD Model

Designers build a 3D model using Computer-Aided Design (CAD) software. This model defines dimensions, tolerances, and other part features. This is also where Design For Manufacturing (DFM) principles come ensuring your design is optimised for cost-effective machining.

Step 2: Convert CAD to G-code

Using CAM software, the CAD file is converted to G-code, which contains all toolpaths and machining parameters.

Step 3: Prepare the Machine and Workpiece

Operators secure the material to the machine bed and insert the appropriate cutting tools. Tool offsets, fluid systems, and other settings are configured.

Step 4: Execute the Machining Operation

The CNC machine follows the G-code instructions to cut away material and shape the part. Some jobs may require manual tool changes or repositioning.

Step 5: Post-Processing

Depending on the application, parts may be bead blasted, anodised, powder-coated, or polished for enhanced functionality or appearance. Explore options like bead blasting, anodising, and powder coating in our CNC machining surface finish gallery.

Watch this short video for a visual explanation of how CNC machining works from design to production

CNC machining is one of the most widely used manufacturing methods in the UK particularly valued for its precision, repeatability, and speed. But how does it compare to other technologies like 3D printing or injection moulding?

In the UK manufacturing sector, CNC machining is often the go-to choice when accuracy and material performance are non-negotiable, as in aerospace engineering, medical prototyping, or precision components for industrial machinery.

While additive manufacturing offers more design freedom, CNC machining is often faster for fully functional parts and delivers better mechanical properties, especially in metals.

CNC Milling

The most common form of CNC machining. A rotating cutting tool removes material from a stationary block. CNC mills can cut flat surfaces, slots, holes, and complex 3D shapes.

• 3-axis CNC milling: Movement on the X, Y, and Z axes
• 5-axis CNC milling: Adds rotation to either the tool or workpiece, enabling complex, multi-sided cuts in one setup

Geomiq offers a professional CNC milling service for both prototype and production parts, with capabilities spanning 3-axis to full 5-axis machining.

For an in-depth look at techniques, machines, and tips, explore our complete CNC milling guide.

CNC Turning

In this process, the workpiece rotates while a stationary cutting tool shapes it. Turning is ideal for cylindrical parts, like shafts, pins, and bushings.

Key turning operations include:

• Straight turning
• Taper turning
• Facing
• Grooving

Machines used: CNC lathes and turning centres (some with milling features).

For details on tools, machines, and use cases, see our full guide on CNC turning.

CNC Drilling

Drilling machines use rotating drill bits to make precise holes. CNC mills can also drill, but dedicated CNC drills offer better speed and efficiency for high-volume hole making.

These machines often use a gantry x-y motion system to move the cutting head efficiently across large flat workpieces.

Common applications:

• Holes for fasteners
• Tapping and threading
• Boring and countersinking

CNC Routing

Used for lightweight materials like wood, plastic, and foam. Routing is a surface-level operation ideal for signage, patterns, and engraved parts.

Routers prioritize speed and precision over torque and often include:

• Gantry-style design for large, flat sheets
• Light-duty cutting heads
• 2.5D or limited 3D capability

CNC Cutting

“Cutting” typically refers to slicing flat sheets using high-energy or high-speed media. It’s common in sheet metal fabrication and works well for 2D parts.

Types of CNC cutting:

• Laser cutting: Uses a focused laser to melt or vaporize material.
• Waterjet cutting: High-pressure water (with or without abrasives) slices through various materials. Geomiq’s waterjet cutting service supports a wide range of materials and produces clean edges with no heat-affected zones.
• Plasma cutting: Electrically conductive plasma arc melts through metal.

CNC cutting is widely used in sheet metal fabrication for applications such as enclosures, brackets, and panels.

CAD (Computer-Aided Design)

Used to create accurate 3D models of the part, including dimensions and tolerances. Common CAD file types: STEP (.stp), IGES (.igs)

CAM (Computer-Aided Manufacturing)

Converts CAD models into G-code - the machine-readable instructions that control speed, toolpaths, and depth of cut. CAM software also allows for toolpath simulation to detect errors before machining begins.

CAE (Computer-Aided Engineering)

Used for simulation and analysis. Engineers use CAE to assess stress points, thermal performance, and material deformation through tools like FEA and CFD.

Common CNC Machining Metals

Metals are the most used engineering materials, so it is no surprise that they are the most machined. Various types of metals and metal alloys have different properties and applications. The table below details the most common CNC machining metals.

View the full list of compatible metals and plastics in our CNC machining materials catalogue.

Common CNC Machining Plastics

CNC machining can also manufacture products from various rigid plastics. However, it is important to take fume safety precautions when machining plastics, as certain plastics release toxic fumes at very high temperatures. The table below shows the properties and applications of some of the most common CNC machining plastics. See our CNC plastic machining article to learn more.

Learn how to machine ABS, PEEK, PTFE, and more in our detailed CNC plastic machining guide.

Aerospace: Engine parts, ducts, and lightweight components

In aerospace hubs like Bristol and Farnborough, 5-axis CNC milling is frequently used to machine aluminium and titanium components such as turbine casings, cooling ducts, and structural brackets. 

These parts must meet strict tolerance requirements and perform under extreme pressure and temperature conditions.

Automotive: Gears, housings, and custom fittings

Automotive manufacturers and suppliers throughout the Midlands use CNC turning and milling to produce precision gears, engine housings, and transmission components. 

Rapid CNC prototyping is also a key part of the electric vehicle (EV) development process, helping startups iterate parts before moving into tooling or casting.

Medical: Implants, surgical instruments, prosthetics

In cities like Manchester and London, CNC machining supports the production of custom orthopaedic implants, surgical cutting guides, and complex prosthetic devices. 

Titanium and cobalt-chrome parts are milled with micron-level precision based on patient-specific scans, ensuring optimal fit and biocompatibility.

Discover how CNC is revolutionising healthcare in our medical CNC machining spotlight.

Consumer products: Electronics, tools, and furniture hardware

CNC machining is a go-to for design studios and product developers creating high-quality consumer goods. 

It’s used to prototype or batch-produce components such as device enclosures, kitchen tools, audio equipment parts, and luxury furniture fittings-especially when a polished or anodised finish is required.

Industrial machinery: Fixtures, housings, mechanical parts

UK manufacturers in energy, food processing, and packaging often rely on CNC machining for the creation of replacement fixtures, housings, and structural frames. CNC allows for fast, reliable turnaround-especially when legacy parts are no longer available from OEMs.

Non-industrial: Art, signage, furniture, and custom design

In creative industries, CNC routers and mills are used to carve custom signage, one-of-a-kind furniture, architectural models, and set pieces. Artists, fabricators, and interior designers frequently turn to CNC for its repeatability, speed, and ability to translate digital concepts into tactile reality.

We’re fully accredited with ISO 9001:2015 and ISO 13485:2016 certifications-critical for producing high-quality medical devices in the UK and beyond.

Advantages

• Precision & accuracy – Tight tolerances and repeatability
• Speed – Quick turnaround from design to part
• Material versatility – Metals, plastics, wood, foam, more
• Complexity – Capable of intricate geometries
• Scalability – From one part to hundreds

Limitations

• High setup cost – Especially for short runs or complex setups
• Material waste – A subtractive process means scrap is inevitable
• Slower for high-volume production – Not ideal for millions of parts
• Design constraints – Sharp internal corners and thin walls may need redesign