CNC Machining Basics

An introduction to CNC machining and the basics of turning and milling

What is it CNC?

CNC (Computer Numerical Control) machining is a subtractive manufacturing process that uses computer-guided tools to remove material from a solid block (or “billet”) to form a precise part or component.

CNC machining plays a vital role in the precision engineering. From small-batch prototypes to high-tolerance production components, this technology allows consistent delivery and repeatable accuracy across a wide range of materials — particularly stainless steels, aluminiums, and plastics, which are common in the subsea and offshore sectors.

In this article, we’ll walk through the fundamentals of CNC turning and milling, share how we approach setup and process control, and offer a practical introduction to how different materials respond to machining.

There are multiple types of CNC machining, but this article will focus on turning and milling operations.

CNC Turning – Involves rotating the workpiece on a lathe while a cutting tool shapes the external or internal surfaces (e.g. shafts, threads, bores). In simple terms, a turning is a process generally reserved for producing round shapes, from round material, with a couple of slight exceptions.

There are many CNC lathes available now which are also capable of undertaking milling operations, such as a lathe with driven tooling used for creating slots and flats. It is therefore possible to complete milling operations, on a machine which would more generally be considered a lathe, because turning is it's primary function.

CNC Milling – Uses a rotating cutting tool to remove material from a stationary workpiece in multiple axes (e.g. slots, pockets, profiles, contours). In simple terms, milling is a process more reserved to creating more geometrically complex shapes, than those in a lathe.

Programmers, Operators and Setters.

Historically, CNC machining relied on three distinct roles:

Programmers who created the part program, either manually using G-code or through CAM software, translating drawings into machine instructions.
Setters who prepared the machine for production: installing tools, loading the program, setting work offsets, and running first-off checks.
Operators who monitored the machine during production, loaded raw materials, and inspected finished parts to ensure consistency.

This workflow offered clear division of labour, especially in high-volume manufacturing. However, with the rise of integrated CAD/CAM systems, these roles are increasingly being merged, particularly in small-to-medium-sized batch work.

Today, it’s common for a skilled machinist to handle programming, setup, and operation as one continuous task. Modern software streamlines tool path generation, and with 3D simulation and verification tools, a single person can confidently prepare and run complex jobs, such as Fusion 360.

The use of CADCAM software by no means removes the skill from the job, it is simply a modern tool which can speed up the programming operations. The machinist still needs to have in-depth knowledge of tooling, feeds, speeds and more.

Understanding Materials

Different materials present very different challenges during machining. Here’s a closer look at how we approach the three most common families of materials we work with:

Stainless Steels

Stainless steels, such as 304 and 316, are known for their excellent corrosion resistance and mechanical strength, both are essential in harsh marine environments. However, they can be challenging to machine due to their tendency to work-harden. This means that if the tool rubs rather than cuts cleanly, the material becomes harder as the process continues, leading to tool wear and poor surface finish.

To counter this, it is essential to use high-quality cutting tips, such as coated carbide tools, and optimised feeds and speeds for the operation being completed, such as drilling or tapping. Coolant application is particularly important to manage heat buildup and chip removal.

Aluminiums

Aluminium alloys, like 5083 or 6082, are popular for components that need to be strong but lightweight. These materials are generally easier to machine than stainless steel and allow for higher spindle speeds and faster machining cycles. However, aluminium can sometimes produce long, stringy chips and is prone to forming a built-up edge on the tool if not machined aggressively enough.

We machine aluminium using high-helix cutters, polished flutes for clean chip evacuation, and in some cases, dry or mist-cooling techniques that help maintain excellent surface finish.

Plastics

Engineering plastics such as Acetal(Delrin), Nylon, and PTFEare frequently used for insulating components, seals, or wear-resistant parts. These materials don’t behave like metals during machining because they’re softer, more elastic, and can deform under pressure or heat.

When machining plastics, we reduce spindle speeds, increase feed rates, and select tools with very sharp, polished edges. Because plastics can melt or smear when overheated, it is possible to machine them dry or use air blasts to clear chips without introducing unnecessary heat. Fixturing must also be carefully designed to avoid distorting the part during clamping.

When manufacturing components for the subsea industry, parts commonly machined from Stainless Steel include load bearing items such as clevis or load pins, electrical connectors, shafts and other structural parts. Aluminium is commonly used for housings, brackets, pressure-tight and enclosures for shallower water depth. When selecting items to be manufactured from plastics, it is common to use certain grades for sealing components, wear plates or isolators between different grades of metal.

Summary

CNC machining remains one of the most essential processes in modern engineering and manufacturing, not just for its ability to create precise, complex parts, but for the repeatability, scalability, and versatility it brings to almost every industry.

Whether it’s a one-off prototype or a critical production component, CNC machining allows engineers to move from digital design to physical product with a high degree of control. It bridges the gap between concept and reality.

At Vulcan Offshore, CNC turning and milling are more than just manufacturing methods; they’re tools that help us meet the demands of high-integrity applications in subsea, offshore, and precision engineering environments. As materials, software, and machines continue to evolve, CNC machining remains a foundational part of building the future.