Engineers Guide to CNC Machining

By Luke Smoothy | 26/11/2020

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Mechanical, manufacturing and design engineers often rely on CNC Machining to develop and manufacture bespoke parts. A good understanding of CNC Machining is essential for engineers so they can understand the benefits and limitations of the process. CAD software and the end use of the final part may vary from project to project, however, the fundamental principles of CNC Machining remain the same. This guide aims to provide engineers with greater insight into the important factors that they need to consider when designing a part for CNC Machining.

What is CNC Machining? 

CNC Machining is a manufacturing process that uses subtractive machining technology and Computer Aided Design (CAD) to manufacture high-quality components. CNC stands for Computer Numerical Control. During the CNC Machining process data input is driven from the digital 3D CAD file, having a computer control this process means there is a reduction in lead times and also reduced human error, leading to a high-quality and highly precise output.

CNC Machining can be used for bespoke, one-off parts all the way through to mass production runs.

In order to fully benefit from the mass production and high-quality parts that CNC Machining offers, engineers should be aware of how CNC Machining works and fundamental factors that affect the process.

This guide considers these various factors, including:

  • The cost of CNC Machining
  • Considerations for Engineers
  • Tolerances
  • What are the tolerances in CNC Machining?
  • CAD File Formats
  • Best CAD Software for Engineers
  • Types of CNC Machine

The cost of CNC Machining

The cost of CNC Machining varies from project to project and depends on the material, complexity and quantity of the parts to be machined. Other factors such as how the end product will be used, and additional finishes and tolerances will influence the cost also. Most materials can be CNC machined, including most metals and plastics. Wood, foam and composites can also be CNC machined, however, Get It Made specialises solely in metals and plastics. Less dense materials are typically quicker to machine as the CNC Machine can operate at a higher feed rate. Reducing machining time is one of the key drivers for reducing the cost of CNC machining.

Request a free CNC Machining quote from Get It Made today

Considerations for Engineers

Further considerations that engineers should be aware of when designing a part for CNC machining include the overall part size and the number of reorientations required to machine the part. These directly influence the machining and setup time. This not only affects the cost of the part but also the lead time. If you require CNC parts fast, look to reduce the complexity of the design and ensure the machining can be completed in as few operations as possible.

Read our detailed CNC Machining Guide here

Tolerances

Engineers need to use realistic tolerances on initial drawings and designs that reflect how the final part will be used and how it interfaces with other parts. Overly tight tolerances increase costs and lead times, therefore try to determine the tolerance you require as opposed to specifying a generic tolerance. 

cnc machining engineering drawing tolerances

What are the tolerances in CNC Machining?

Tolerance refers to the range for a dimension, and a designer or engineer will determine the tolerance based on the form, function, and fit of the part. Most parts will have a maximum and minimum dimensional limit. Standard CNC tolerances are determined by the type of CNC process being applied, for example, the CNC tolerance in CNC turning can be controlled more tightly than that of CNC machining.

There are many different types of tolerances, such as positional, flatness, parallelism, thread tolerances etc. We recommend familiarising yourself with GD&T (Geometric Dimensioning and Tolerancing) which is a methodology and language for communicating engineering tolerances.

You can find more information on the types of metal used in CNC machining by reading this guide, Choosing the Right Metal for CNC Machining.

CAD File Formats 

CAD file formats are another factor for design engineers to consider when designing a part for CNC. Various software packages and file formats may not be compatible with CNC machining, and it is important to consider the type of CAD software you are using, too. 

You can read our detailed guide on CAD File Formats for CNC Machining here.

Best CAD Software for Engineers

To create CAD files to input into a CNC machine, a CAD software package is needed. The CAD software you choose will depend on the cost, ease of use, and file compatibility of the software. The five industry-leading CAD software packages are:

  • SolidWorks
  • Autodesk Inventor
  • Creo
  • Siemens NX 
  • Catia

You can read more about CAD software in our detailed guide to CAD software for CNC Machining

Types of CNC Machine 

CNC Machining is sometimes used as an all-encompassing term to describe the various different types of computer-controlled subtractive machining technologies such as:

You can find our detailed Guide on Types of CNC Machine here.

To find out more about our range of CNC Machining services, arrange a free quote today or discover our range of CNC Machining services here. Head to our technical toolbox for our full complete range of machining knowledge.

Luke Smoothy

Director and Founder of Get It Made Ltd.

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