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An Introduction to CNC

Introduction to CNC

If you’re new to the world of CNC (or computers) then the technical nature of a lot of the informationcan make it seem like a difficult subject to unlock. Here, we’ll help you understand the basics of CNCand explain some of the most important concepts and technical jargon.

What is a CNC?

The term “CNC” is a generic term which can be used to describe many types of device, this wouldinclude plotters, vinyl cutters, 3D printers, milling machines and others. CNC stands for ComputerNumerical Control and basically means that the physical movements of the machine are controlled byinstructions, such as co-ordinate positions that are generated using a computer.

The term “CNC Machine” is typically used to refer toa device which uses a rotating cutting tool that movesin 3 or more axes (usually X, Y and Z) to cut out orcarve parts in different types of materials.The information on these pages will focus on whatare typically referred to as “CNC Routers” although itwould be applicable to most CNC milling and engravingmachines as well.

So what can you make with a CNC?

CNC machines are incredibly versatile and allow you tocut or engrave a variety of different types of product andmaterials. The exact abilities of a machine will vary withsize, rigidity and power. Typically most CNC Routers cancut and engrave soft and hard wood, plastics, othercomposites and non-ferrous metals.

CNC users range from hobbyists who build their ownmachines through to large companies with industrial

equipment costing hundreds of thousands of Rands. With the right software a CNC machine canmake a huge selection of things.

Getting Started With CNC

As with any subject, the more time you invest in learning about CNC and related technologies, themore you will get from it. The following are some of the key areas that are important for you tobecome familiar with.

Computer skills

One requirement common to all aspects of CNC work is how to use a computer to perform basictasks. You may also need to use a combination of software to design and cut your parts. This willrequire an understanding of starting and stopping software programs, saving, copying, moving anddeleting files, finding files stored on your computer and installing programs and updates. If you don’tfeel comfortable with your current computer skills or are new to running a PC then it would be wellworth taking a basic course or buying a general guide to working with your PC.

Design & Toolpath Software

Before you can cut anything with a CNC Router, you will needto first create the design layout that the machine is going tofollow to cut or engrave the parts. The software you choosefor this will play a significant role in successfully creatingyour CNC projects.

Simply put, the design and machining (toolpath) software will allow you to transform “pencil andpaper” ideas to a set of instructions used to run the machine. When done correctly, the end result willbe a physical product that has value and purpose and a great sense of achievement.

Operating and Maintaining your CNC Machine

If you currently own or use a CNC machine, you already know how important it is to be aware of itslimitations, and to work within them. You will also understand that you need to keep it properlymaintained and know how to set it up correctly to run a job.

If you don’t own a machine yet, then it’s important to spend time thinking about what you want yourmachine to be able to produce. This can help eliminate a lot of potential future frustration. Cost willalways be an important factor, but that also needs to be balanced against its capabilities, becausenothing can be more expensive than a machine that cannot do what you need. For example, if youwant to cut large sheet goods then a smaller model will not be the best choice. However, if you havelimited space then this may be your only option and you need to understand its limitations on howlarge a part it can cut. Only you can determine what this balance will be for your situation and budget.

Some important considerations when researching the purchase of a machine include size, speed andaccuracy and the technical support offered both before and after the purchase. As with software, theimportance of a company’s reputation and support cannot be overstated.

Every CNC machine needs software to directly drive its movement; this is commonly referred to asthe “Control Software”. This takes the instructions created in the Design and Machining program andturns it into physical movement with the machine’s motors. A common package that does this isMach3. Many manufacturers create and use their own proprietary systems as well. The controlsoftware may be installed on an external PC or be loaded onto a dedicated Control Box which is partof the machine.

Knowledge of Materials and Tooling

When it comes to obtaining the best possible results, another essential set of factors are the materialyou are working with and the tool you are using to cut or engrave it. Material choice will affect everystage of the Project – from initial concept through to final finishing.

The most common materials people using CNC Routers work with include; wood, plastics, densefoam board and softer (non-ferrous) metals (brass, aluminium, etc.). If you are not already familiarwith the type of material you want to use, there are many sources of information online.

To efficiently and safely cut or engrave your choice of material you will need to choose an appropriatetool (bit), know how fast you can move the tool through the material (Feed Rate and Plunge Rate),

how much material you can remove at one time (Pass Depth and Cut Depth) and how fast the bitshould be rotating (Spindle Speed). Typically suppliers of tooling offer technical information on thecorrect settings for cutting different material types with the router bits they sell.

On the internet you will find many good sources of information from material and toolingmanufacturers’ websites. Another excellent resource is ask questions and read about other users’experiences with different tools, materials and settings on Online Forums.

When looking at a complete CNC project from start to finish, you can identify a series of major stepsthat will form the Workflow to complete it. Having a good understanding of this process will help youstart to appreciate where the different software packages and setup procedures fit into the overallcreation of parts. Below is an overview of the different stages.

A) Concept

The idea for what you are going to make. This may range from a specific customer requirement,something you have sketched on a piece of paper, or a ready-to-go file that someone has alreadyprepared. At this stage you should review what it is you are making. Try and think through theprocesses in the job to help to get the best approach to achieving it. You should also assemble anyreference material you will use to help design the part such as photos, data from the customer,design sketches etc.

B) Design

For the design, you need to create the computer data that will define either the 2D or 3D forms youwant to cut or engrave on your CNC machine. This is done in what is typically called CAD (ComputerAided Design) software and you may also hear this type of software referred to as a drafting, drawingor design program.

The finish point of the Design stage is to have prepared all the 2D data (Vectors) or 3D data(Components) that you require to start calculating the specific movements the CNC machine willfollow. These moves are typically referred to as the Toolpaths.

There are many CAD programs available for either 2D drawing or 3D modeling and depending on thefile format export options available, this data can be saved and used with your CNC machine.

C) Toolpaths

Once the design is complete, you will need to usea software package (like LazyCAM) to calculatethe actual paths that will drive where the tool willmove on the machine.

Creating your Toolpaths is the key stage in goingfrom the virtual world of computer design to thereality of the physical world.

At this point you will need to take into account theshape and size of the tool that you need to use, thetype of movement you want the tool to make(the shape you want it to leave in the material) andappropriate settings for how fast the tool can bemoved and how much material can be safely removed.

When the Toolpaths have been calculated, the software will let you preview how they will look. Thislets you check that they are doing what you expected. Once you are happy the Toolpaths are correct,then they can be saved in a format that is appropriate for your particular CNC - normally GCode.

D) Machining

Once your Toolpaths have been saved, you will open them in your CNC software (If you are usingMach3, you will import the GCode). At this stage you will need to adjust various settings and positionson your CNC to match the job setup you specified in the Design/Machining software.

This will involve setting up your material in theright orientation, and making sure it will be securewhile you’re cutting or engraving it. Then you needto load the correct tool and tell the machine wherethe X, Y and Z reference position is for the tool tip.Typically this location represents the zero positionfor each axis.

Once the machine is set up correctly, theToolpaths can be loaded and then executed fromthe CNC’s control software. The software will feedthe co-ordinates of the Toolpaths to the machineto continually move its position and create the image you set up. Running the Toolpaths may takeless than a minute or potentially many hours - depending on what type of operation it is.

E) Finish and Assembly

Finish and assembly are obviously going to vary dramatically depending on the type of job you aredoing and the material you are working with. Some projects will be ready to use when they come off

the machine without further finishing work being required, and some may need sanding or additionalhand-carving to get the final shape.

Ultimately what you are making may need priming and painting or multiple coats of stain or paint toget the required colouring. The finished part may also require assembly, fastenings or glue if itinvolves multiple pieces.