Cutting tool basics A cutting tool is a device used to remove material from a solid block of material. It is fitted to the spindle of a CNC machine, which follows computer instructions to guide the cutting tool where it needs to go. Cutting tools remove material from the workpiece by a process of shear deformation. That is, the sharp tool rotates at high speed and cuts from the workpiece many tiny chips, which are then ejected away from the workpiece. Some tools make contact with the workpiece at one point only, while others, such as end mills, hit the material at multiple points. The type of cutting tool will affect the size of chip removed from the workpiece, and so will the spindle speed and feed rate. Common cutting tool materials include Carbon steel Carbon steel is an affordable steel alloy containing 0.6-1.5% carbon, as well as silicon and manganese. Carbide Usually sintered with another metal like titanium, carbide tools are wear-resistant and heat-resistant, providing an excellent surface finish. Ceramic Used to cut superalloys, cast iron and other strong materials, ceramic tools are resistant to corrosion and heat. High-speed steel The more expensive HSS is harder and tougher than carbon steel thanks to its blend of chromium, tungsten and molybdenum. Cutting tool coatings The function of a cutting tool depends on its shape and material, but can also be adjusted with a coating over the main material. These coatings can make tools harder, increase their lifespan or enable them to cut at faster speeds without compromising the part.