Computer numerical control is a very broad term that encompasses a variety of types of machines—all with different sizes, shapes, and functions. But the easiest way to think about CNC is to simply understand that it’s all about using a computer as a means to control a machine that carves useful objects from solid blocks of material. For example, a CNC machine might begin with a solid block of aluminum, and then carve away just the right material to leave you with a bicycle brake handle. CNC machines can be divided into two groups: turning machines and milling machines. A turning machine is generally made up of a device that spins a workpiece at high speed and a tool (sharp edge) that shaves off the undesired material from the workpiece (where the tool is moved back and forth and in and out until the desired form is achieved). A milling machine is a machine that has a spindle (a device similar to a router) with a special tool that spins and cuts in various directions and moves in three different directions along the x, y, and z axes. Historically, you wouldn’t actually need a computer to create forms with a turning machine or a milling machine. Adding a computer to the mix allows you to design a product on a computer first and then specify how the machine should cut this product. To design the product is to produce a computeraided design (CAD) file. Then you specify how the machine should cut the product, and the result of that step is a computer-aided manufacturing (CAM) file (or G-Code file, or .NC file—there are many names for this type of file). This CAM file remembers all of the operations that the milling machine must follow to cut out the parts for the product. The computer tells the CNC machine how to build the part by interpreting the CAM file into signals that the CNC machine can understand.
Industrial Uses
Industrial applications for CNC machines have been chiefly based around the removal of metal to create a desired form. Metal is widely used for producing almost everything we see around us, even though these things may not be made of metal themselves. Some of the most obvious products that are made of metal are cars. The engine block and the parts within the transmission are directly produced from a CNC machine because tight tolerances are necessary (a tolerance is a range in dimensioning to which the machine must adhere). However, most of the parts of a car are not made by a CNC machine, but they have a latent connection to one. For example, how do you make a quarter panel? There is a hydraulic press with a thing called a die to create an impression in a sheet of metal. Most of the parts of the hydraulic press were made from a CNC machine. The die, the part that carries the negative form of the quarter panel and that can be replaced when design changes, was also made by a CNC machine, and then tempered for hardening and heat resistance. Even the plastic parts of a car have some connection to a CNC machine. Many of these parts were made from a mold that was created using a CNC machine. Because CNC machines have very high precision and they can provide information back to the computer, they are also used in dimensional testing. If a switch (probe) is fastened to the location of the tool, it can analyze the measurements of a part that was produced. The machine runs this probe all over the part to confirm its desired form and measurements.
Personal Uses
There is a large following by various hobbyists and DIYers around the globe interested in the concept of CNC machines. Roboticists, craftsmen, handymen, home machinists, small business owners, tech enthusiasts, backyard scientists, and artists have all discovered how a CNC machine can open doors to new designs and more detailed creations. A roboticist, for instance, will use a CNC machine to create the structural components of the robot with very high precision. Making these components by hand would be tedious and very time consuming. Using a CNC machine, the parts come out beautifully and fit together with great precision.
For the typical handyman, a great example of using a CNC machine might be designing and making cabinets for around the house. Typically, cabinets share many of the same dimensions and can be cut by a CNC machine over and over. Imagine cutting all of the drawers and cabinet lids by hand! The parts are numerous and the work would be quite tedious. But with a CNC machine, the individual pieces are cut and the cabinets assembled; no driving around looking for the right cabinets, having to special order them, and then waiting for delivery from the home improvement store. (The cabinets will need assembly, too, but with your own CNC machine, you’ll find that the high cost of buying them in the store can be eliminated.) CNC machines for personal use can be purchased from a variety of manufacturers, but many DIYers suffer from sticker shock the first time they begin shopping for a CNC machine. Prices of $3,000 and
higher are typical for small, desktop versions that often come with a 12"×18" workspace, meaning you’ll be limited to working on materials that fit in that small space. CNC machines with workspaces that allow for materials of 2'×4', for example, start around $7,000, and prices go much higher for larger workspace tables. For most DIYers, owning their own CNC machine is still out of reach financially. But no longer—this book brings CNC within easy reach. If you can afford to spend $700 to $800, then you can afford to build your very own CNC machine.
