What is CNC Machining?

An introduction to CNC Machining

26
Mar

What is CNC Machining?


CNC Machining is seen by many as a vital element to core processes of manufacturing. Working alongside Computer Aided Design, CNC Machining is the process of mass producing parts and materials of specific designs and dimensions, through the use of computer numerical control. That is to say, a computer directs the machine responsible for creating the final product.

cnc machined part This guide will cover the following:

  1. What is CNC Machining and how does it work?
  2. Why is CNC Machining popular?
  3. Benefits of CNC Machining 
  4. What materials can you use?
  5. What is the process of CNC Machining?
  6. Types of CNC Machining 
  7. CNC Milling
  8. CNC Turning
  9. CNC 5 axis machining (multi axis)
  10. Limitations of CNC Machining
  11. CNC Machining finishes

 

What is CNC Machining and how does it work?


At its core, CNC Machining involves the processes of subtractive machining technology. Simply speaking, its technology works through material removal mechanisms, which, following input from computer aided software, creates the product. This is achieved through cutting tools, which shape and ‘cut’ the final product from a solid block, also known as a blank, or a workpiece. 

Top Tip: You can read up on Get It Made’s processes of CNC Milling & Machining here.



The growth in popularity of CNC Machining stems from the high accuracy and quality finish that can be achieved. Why? Because the final piece has been crafted from a CAD file. With Computer Aided Design and therefore high automation, comes lesser chance for error.

For this reason, CNC prices are competitive, for both one-off custom parts, as well as medium volume productions, however you can find companies who will work with you to keep costs down while still delivering a high quality product. If you are in need of CNC Machining quote, contact Get it Made to get started.  

CNC Machining is used in multiple industries due to the reduced risk of human error and high accuracy, precision made products. For industries where mass production, cost efficiency and accuracy are essential, CNC Machining techniques are seen as integral to the production process.  


Benefits of CNC Machining


  • Convenience
  • Accuracy 
  • Simplifies processes
  • Cost efficient 
The complexity and intricacy of high performance engineered parts requires a complex and intricate system that is up to the task. CNC Machining capabilities such as those Get It Made can provide are widespread, and have been specifically designed to cope with the demand for high precision products. 

Industries that regularly utilise CNC Machining on a daily basis:

  • Medical industry
  • Aerospace industry 
  • Transportation industry 
  • Oil and gas industry 
  • Military and defence industry 
  • Electronics industry 
  • Marine industry 
  • Subsea industry 
 

What materials can you use?


CNC machining can use plenty of materials – as long as the materials themselves are of a certain strength to withstand the process. 

Selecting the right material is crucial. 

Almost all materials can be CNC machined; the most common examples include:  
  • Metals such as aluminium, steel alloys, stainless steel and brass 
  • Plastics such as ABS, polycarbonate, nylon, POM and PEEK.
There are some restrictions, including a minimum wall thickness and maximum aspect ratio for some designs, as the material must be able to withstand the pressure and, at times, vibrations of the cutting tools during the crafting process. 


What is the process of CNC Machining?


In general, CNC machining can be split into three core steps:
  • Engineers designing a CAD model of a part
  • The machinist turning this CAD file into a CNC program, setting up the machine
  • CNC program then relays the various steps to the CNC machine, that, with little supervision, creates the part.
This system of delivery is part of the reason why CNC machining is so popular, as there is little room for human error, as we touched on earlier. Relying on computer aided design can ensure maximum accuracy – digital manufacturing, however, can have its limitations (which we will discuss below).


Types of CNC machining


CNC Machining can be broken into various types, including:  
  • CNC Milling
  • CNC Turning
  • CNC 5 Axis machining (multi-axis)
 

CNC Milling 


cnc machined part With CNC Milling, the workpiece is held stationary on the machine bed, and held in place via a vice. The process of subtractive machining technology then works by material being removed from the blank workpiece by cutting tools and drills. 

These drills and tools rotate at a high speed, their purpose is to remove material from the workpiee using instructions originating from the CAD design in the early stages of development.

These tools are attached to a spindle, and, in the case of CNC Milling, move along a 3 linear axis. 

Our beginner's guide on CNC Milling can help you with any specific questions you may have about the process. In a nutshell, however, it is a popular choice for producing industrial products and parts.

There are occasionally limitations to CNC Milling – as there are commonly 3 axes to work with, there may be areas the cutting tools might not be able to reach. Multiple rotations, extra labour and machining costs will need to be considered at this point. 

Parts which require CNC milling will usually be produced if they have simple geometries, which a 3 axis machine can comfortably work with. It is easy to program and operate a 3 axis milling machine, meaning there is excellent accuracy and low cost.


CNC Turning / Lathes 


cnc machined part The workpiece is kept in position on the spindle while rotating at high speed. CNC Turning techniques are the lowest cost per unit and are only suitable for part geometrics with rotational symmetry. For example -  washers and screws can be mass produced using CNC lathes.

CNC turning is a cost friendly option if you are mass producing symmetrical parts. CNC lathes are extensively used to produce parts at a much higher rate, and lower cost per unit. 

Find out about Get it Made’s CNC Turning services here. 


Process of CNC Turning 


The bar or workpiece is held on the spindle while rotating at high speed, while the cutting tool or central drill traces the inner/outer perimeter of the part, forming the geometry. The tool does not rotate with CNC Turning, and rather moves along polar directions radially and length wise. 


CNC 5 Axis machining (multi-axis)


More complicated, intricate designs that may not follow the simple designs of a 3 axis CNC milling machine may need the use of a 5 axis CNC milling machine. As the name suggests, this machine operates through the use of 5 axes, as opposed to 3. Due to a higher number of axes, more complex design models can be configured. 

This does, however, come at a higher cost! 

With more freedom and more rotation flexibilities, advanced capabilities can be met. However, specialised machinery and operators may cost you more, so when you are in the CAD stage of your product, aim for your designers to make the vectors as simple as possible. Access to the workpiece can be achieved from a different angle with the 5 Axis model, meaning the machine bed and toolhead can also move along with the three access points. 

Use 5 Axis Machining for:

  • Complex features
  • Organic designs
  • Smooth contours
 

What are the limitations of CNC Machining?


Internal hidden geometrics can be problematic, with a limit to the maximum depth of the undercut. Workpieces, too, can deform and vibrate – during production, the cutting forces a temperature change that can result in deformations, meaning that, in some cases a design may be too intricate for the standard 5 axis CNC processes. 

Deep cavities, similarly, cannot be easily CNC machined – tools can deflect and vibrate during machining (known as chatter), and with looser tolerances, tool breakage can occur. Additionally, manual repositioning may be needed. 

In essence, the geometry of a part determines the way it will be held on the CNC machine, reflecting the number of setups required. Although automation is nowadays considered far more efficient than human processes, the fact that it is automated doesn’t leave a clear path for trickier designs. 

Bearing this in mind, when you’re designing a part, you should likely consider:
  • Hole depth 
  • Wall thickness
  • Internal radii
  • Cut depth
  • Type of corner – square corners are more costly as the cutting tools are rounded in shape
Read more about Part Design Impact in our blog focusing on CNC tips and tricks. 


Factors that affect the CNC Machining process


When developing your 2D CAD model, it’s important to consider factors such as:
  • Minimum part thickness
  • Maximum part size
  • Complexity of internal cavities / features

CNC Machining finishes


cnc part finished red The surface finish is another consideration to make. 

Alongside the material itself, there will be different surface finishes including:

  • Grinding
  • Polishing
  • Bead Blasting
  • Electroplating
  • Knurling
  • Honing
  • Anodising
  • Chrome Plating
  • Powder Coating

Depending on the recipient in the supply chain, be that another supplier, a client, or a customer, the finishing of the part will likely be different. For example, in some cases, factory standard finish will be acceptable, however in some cases a more high-quality finish or coating may be required. This will depend on the industry, as well. Surface finishes will alter factors such as:
  • The product’s appearance
  • The surface texture
  • Roughness/hardness of finish
  • Chemical resistance


Get It Made prototypes and manufactures bespoke parts through CNC Machining, and with every project meticulously planned for efficiency and value. You can contact us today to find out more about who we are, what we do, and how we may be able to help your business.