CNC Machining 101: Get to Know the Basics

From simple, mass-produced everyday items like mobile phones and electrical consumer goods to complex components in airplanes, cars, and motorcycles or sophisticated medical, manufacturing, and construction products, CNC machining have transformed the way we produce millions of items. 

These machines form an integral part of virtually everything we use by providing unrivalled manufacturing speed and precision. It has led to thousands of innovative products that were impossible to produce only a few years ago. 

What Are CNC Machines?

CNC machining is a manufacturing process that uses computerized controls and machine tools to remove stock material from the workpiece and produce custom shapes and designs. Pre-programmed software and code control a range of complex machinery, ranging from lathes, grinders, and turning mills, and can cut, shape, and create the end product in a matter of minutes with no room for human error. Besides speed, accuracy, and consistent results, the CNC machining equipment also produces less waste.

How They Work

From start to finish, CNC machining involves 4 stages: 

• First, a 2D or 3D design of the end product is created using CAD (Computer-Aided Design) software.
• Next, the CAD design is converted to a CNC programme (using G-Code) or dedicated software called Computer Aided Manufacturing (CAM). 
• Before machining begins, the CNC machine is set up with the proper positioning of the workpiece and tooling.
• Machining begins after configuration. The machine removes material from the workpiece until the end product matches the custom design. 

Machining Processes

CNC machines carry out different machining processes and can be classified as such. The most common processes are: 

Milling

This is the most widely used CNC machining process and provides high speed and precision. It involves rotating cutting tools positioned on the machine spindle, moving them relative to the workpiece, and shaping them to the desired dimensions. 

Milling can take different forms. For instance, in plain milling, the cutting tool removes material on the workpiece surface with the workpiece perpendicular to the tool, whereas face milling has grinders or cutters facing down. 

Similarly, angular milling has tools set at an angle to produce details like grooves and dovetails, and form milling is used for contours and curves. Milling produces items like precision medical instruments, car and aeroplane parts (fuselages, axles, etc.), different furniture pieces, and more. 

Routing

This is similar to milling, but the cutting tools move along three axes, and the workpiece remains stationary. This produces faster cuts without forgoing accuracy. CNC routers are used for intricate shapes like carved furniture and musical instruments. 

Turning and Lathes Machines

Here the workpiece is turned around an axis, and a cutting tool is applied. The process is used to produce items as diverse as car engine parts such as pistons and camshafts, table legs, and cricket bats. 

Drilling

Here, the workpiece is held stationary, and drills are deployed over it to make holes. The resulting parts can then undergo further processing or move on to assembly. CNC drills are especially effective on mass-produced wooden items such as furniture.

Grinding

Grinding with a CNC machine means using rotating flat ceramic or diamond grinding wheels to remove stock materials at high speeds. This is also used for sanding, polishing, and smoothing. Parts made with CNC grinders include different car components, engineered parts in different industries, and tools. Similar processes to grinding are honing and lapping.

While these are the main processes, these machines are also used in high-tech industries that use newer technologies such as EDM or electrical discharge machining (when making tool moulds and dies), and laser or water-jet cutting, especially through harder materials. 

Machines and Number of Axes

CNC machines come with a varying number of axes, and this determines the geometries that can be achieved in the end product. Generally, the more axes, the pricier the machine.

2-axis machines are the simplest and cheapest and cut along an X (vertical) and Y (horizontal) axis. They make simple cuts or holes, often by keeping the workpiece stationary. 3-axis variants are some of the most common, and besides the X and Y axes, they can be used for depth or the Z-axis. These, too, operate with a stationary workpiece. 

4,5 and 6-axis CNC machines include rotation (4-axis), pivoting (5-axis), and an additional rotational cutting tool (6-axis) for more detailed and complex cuts. There are also 9-axis variants that combine the functions of milling and turning and 12-axis machines working on all six axes but with two cutting tools working at the same time. 

Pros of CNC Machines

There are numerous advantages to using CNC machines. This relates to reduced waste, greater precision, speedier workflow, increased personnel safety, and lower production costs. 

With machines running optimised software, there’s a lower likelihood of trial and error as in manual machining, but more so in repetitive work that additionally requires parts and components to be produced to tighter tolerances. In this sense, there’s also less material waste, which further reduces costs. 

Furthermore, the whole process is fully automated, so the level of precision is something even the most skilled machinist can’t replicate on manual machines. Machined products are without flaws or defects, and items are produced with uniform consistency. And, since CNC machines can run on their own and perpetually, they lead to faster production and increase efficiency. 

What a CNC machine makes in minutes will take hours on a manual machine, still not to the level of the automated process. The only time CNC will stop is during a power cut, a scenario highly unlikely in the settings where it’s used. 

Additionally, machines reduce the number of workplace incidents and injuries and are capable of working unattended. Employees have a supervisory role and conduct preventative maintenance measures. This means a single employee can oversee several CNC machines at a time, which lowers labour costs. 

And overall production costs are reduced, considering the faster work speeds, higher accuracy, increased product volume turnover, and decreased material waste. 

Materials Used in CNC Machining

A wide range of materials can undergo CNC machining, provided they have sufficient hardness. This includes metals, alloys, plastics, hard and soft woods as well as glass, foam and stone. Most machines aren’t picky about the material they can work on as long as the correct tooling is used. 

Metals  

CNC machines are the quick solution for machining metals into precision parts. Aluminium is one of the most machined materials owing to its low weight, high strength and rust resistance, and the ability to be treated for additional strength and improved appearance. Different Aluminium grades such as 6061 and 7075 are commonly used in CNC machining to produce items like bike frames, laptop housings, car parts, and more. 

Magnesium is used widely for electronics, and where low weight is necessary, such as MAG alloy wheels, whereas cast iron is abundantly used where strength is key, such as hand tools. High-tech equipment needing unsurpassed strength has CNC-machined titanium parts. 

Alloys

Stainless and carbon steel also rival Aluminium and can be easily and precisely machined to the desired item. Typical cases are fasteners such as bolts and screws, and rebar. Brass and bronze are copper alloys seen in decorative fittings, such as door knobs and handrails. 

Plastics 

There are hundreds of types of plastics, and these can undergo CNC machining. This includes Nylon, known for its flexibility and high strength and found in items like spacers and screws used in electronics, ABS plastic commonly seen in product prototypes, Dierin found in automotive parts and construction, PEEK, a plastic alternative to metals used in medical equipment and semiconductors and Acrylic (or Plexiglass) seen in items like aircraft windows and car light housings. 

Summing Up

If you need workpieces cut, sanded, ground, shaped, smoothed, drilled, polished, or treated, there is no faster or more precise method than using a CNC machine. These deploy fully automated workflow, with consistent results in a reduced timeframe and with significantly lower costs. They come in several different types, designs, and price brackets, and can be used on hundreds of different materials. 

Photo by Mastars on Unsplash