DREAM IT DESIGN IT DO IT An Introduction to CNC For help, call 011 036 6062 or 021 839 5594, or send an email to techsupport@perfectlaser.co.za
Introduction to CNC If you re new to the world of CNC (or computers) then the technical nature of a lot of the information can make it seem like a difficult subject to unlock. Here, we ll help you understand the basics of CNC and 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 would include plotters, vinyl cutters, 3D printers, milling machines and others. CNC stands for Computer Numerical Control and basically means that the physical movements of the machine are controlled by instructions, such as co-ordinate positions that are generated using a computer. The term CNC Machine is typically used to refer to a device which uses a rotating cutting tool that moves in 3 or more axes (usually X, Y and Z) to cut out or carve parts in different types of materials. The information on these pages will focus on what are typically referred to as CNC Routers although it would be applicable to most CNC milling and engraving machines as well. So what can you make with a CNC? CNC machines are incredibly versatile and allow you to cut or engrave a variety of different types of product and materials. The exact abilities of a machine will vary with size, rigidity and power. Typically most CNC Routers can cut and engrave soft and hard wood, plastics, other composites and non-ferrous metals. CNC users range from hobbyists who build their own machines through to large companies with industrial equipment costing hundreds of thousands of Rands. With the right software a CNC machine can make 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, the more you will get from it. The following are some of the key areas that are important for you to become familiar with. Computer skills One requirement common to all aspects of CNC work is how to use a computer to perform basic tasks. You may also need to use a combination of software to design and cut your parts. This will require an understanding of starting and stopping software programs, saving, copying, moving and deleting files, finding files stored on your computer and installing programs and updates. If you don t feel comfortable with your current computer skills or are new to running a PC then it would be well worth 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 need to first create the design layout that the machine is going to follow to cut or engrave the parts. The software you choose for this will play a significant role in successfully creating your CNC projects.
Simply put, the design and machining (toolpath) software will allow you to transform pencil and paper ideas to a set of instructions used to run the machine. When done correctly, the end result will be 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 its limitations, and to work within them. You will also understand that you need to keep it properly maintained 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 your machine to be able to produce. This can help eliminate a lot of potential future frustration. Cost will always be an important factor, but that also needs to be balanced against its capabilities, because nothing can be more expensive than a machine that cannot do what you need. For example, if you want to cut large sheet goods then a smaller model will not be the best choice. However, if you have limited space then this may be your only option and you need to understand its limitations on how large 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 and accuracy and the technical support offered both before and after the purchase. As with software, the importance 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 as the Control Software. This takes the instructions created in the Design and Machining program and turns it into physical movement with the machine s motors. A common package that does this is Mach3. Many manufacturers create and use their own proprietary systems as well. The control software may be installed on an external PC or be loaded onto a dedicated Control Box which is part of the machine. Knowledge of Materials and Tooling When it comes to obtaining the best possible results, another essential set of factors are the material you are working with and the tool you are using to cut or engrave it. Material choice will affect every stage of the Project from initial concept through to final finishing. The most common materials people using CNC Routers work with include; wood, plastics, dense foam board and softer (non-ferrous) metals (brass, aluminium, etc.). If you are not already familiar with 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 appropriate tool (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 bit should be rotating (Spindle Speed). Typically suppliers of tooling offer technical information on the correct 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 tooling manufacturers 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 steps that will form the Workflow to complete it. Having a good understanding of this process will help you start to appreciate where the different software packages and setup procedures fit into the overall creation 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 already prepared. At this stage you should review what it is you are making. Try and think through the processes in the job to help to get the best approach to achieving it. You should also assemble any reference 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 you want to cut or engrave on your CNC machine. This is done in what is typically called CAD (Computer Aided Design) software and you may also hear this type of software referred to as a drafting, drawing or 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 will follow. 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 the file 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 use a software package (like LazyCAM) to calculate the actual paths that will drive where the tool will move on the machine. Creating your Toolpaths is the key stage in going from the virtual world of computer design to the reality of the physical world. At this point you will need to take into account the shape and size of the tool that you need to use, the type of movement you want the tool to make (the shape you want it to leave in the material) and appropriate settings for how fast the tool can be moved and how much material can be safely removed. When the Toolpaths have been calculated, the software will let you preview how they will look. This lets 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 using Mach3, you will import the GCode). At this stage you will need to adjust various settings and positions on your CNC to match the job setup you specified in the Design/Machining software. This will involve setting up your material in the right orientation, and making sure it will be secure while you re cutting or engraving it. Then you need to load the correct tool and tell the machine where the X, Y and Z reference position is for the tool tip. Typically this location represents the zero position for each axis. Once the machine is set up correctly, the Toolpaths can be loaded and then executed from the CNC s control software. The software will feed the co-ordinates of the Toolpaths to the machine to continually move its position and create the image you set up. Running the Toolpaths may take less 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 are doing 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 additional hand-carving to get the final shape. Ultimately what you are making may need priming and painting or multiple coats of stain or paint to get the required colouring. The finished part may also require assembly, fastenings or glue if it involves multiple pieces.