CNC (Computer Numerical Controlled) includes not only CNC mills and lathes, but also 3D printers, robotic arms, and other machines. CNC machine tools and 3D printers have much in common, both in the form of a series of coordinates provided in G-code that translate to movements for milling or printing. Through the microcontroller, the given command is converted into the motion of the stepper motor. The basic principles of all CNC machines are basically the same, with the main differences being materials and applications. To better understand machine characteristics and applications, here we focus on the most common machine types among manufacturers, namely CNC milling machines and FDM 3D printers.
1. Molding method: additive and subtractive processing
△ Subtraction processing is more complicated
Processing methods can be divided into two types: additive manufacturing or subtractive manufacturing. FDM 3D printers are used for additive machining, while CNC mills and milling machines are used for subtractive machining. The latter machines include milling machines, drills or milling cutters, which cut and remove material to obtain the desired structure.
Both types of machining require a set of commands like a CNC machine. But because of these methodological differences, there are different ways to get these commands in G-code. By default, CNC mills and routers will start from the surface of a given stock material and cut the desired object from it. To do this, toolpaths need to be created using CAM software. In the software settings, it is necessary to define the tool used, its dimensions and properties, the desired speed, start and end points, and other settings. In addition to this, the process including tool change can be quite complex and requires considerable knowledge.
△Simple toolpath - blue lines for cutting, orange for just moving
If you want to create G-code for a 3D printer, you need to use a slicer. It converts the given object into a sliced image with a certain layer thickness. Each point on the slice is converted to XYZ coordinates. By default, each layer needs to be processed upwards, starting with the build surface. Many slicers provide useful default settings for commonly used 3D printers, which can achieve reasonable slicing paths and results, and can be easily operated by beginners.
2. Motion axis
△ Basic motion axes encountered in CNC machine tools
Most CNC machines, whether they are milling machines or 3D printers, can only operate in three dimensions (i.e. X, Y, and Z axes). There are also some machines that have additional axes such as A, B and C, and some professional high end machines can have up to 12 axes. So, why do we need so many axes? For milling and milling applications, multi-axis operation allows access to the workpiece from virtually any angle, allowing undercuts and complex features not possible with simple 3-axis machines.
Multi-axis printing is new territory for 3D printers. Multi-axis printing can print along the surface contour of the workpiece to improve the accuracy of the printed parts. Using multi-axis printing can build complex structures without support, such as the 5-axis Prusa plus printer.
