Cutting tool (machining)
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In the context of metalworking, a cutting tool (or cutter) is any tool that is used to remove metal from the workpiece by means of shear deformation. Archetypal examples are tool bits, drill bits, and milling cutters.
Technically, grinding wheels are a subset of cutting tools, as grinding is a true metalcutting process. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip that is analogous to what would conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.). However, among people who work in the machining fields, the term "cutting" is most often understood to refer to the macroscopic cutting operations, and grinding is mentally categorized as a "separate" process. This is why the terms "cutting" and "grinding", or "machining" and "grinding", are often used in contradistinction in shop-floor practice, even though technically grinding is a subset of cutting. Consequently, the term "cutting tool" is often used to refer to all cutters used in "regular" (non-grinding) machining, and thus to exclude grinding wheels.
Cutting tools must be made of a material harder than the material which is to be cut, and the tool must be able to withstand the heat generated in the metal-cutting process. Also, the tool must have a specific geometry, with clearance angles designed so that the cutting edge can contact the workpiece without the rest of the tool dragging on the workpiece surface. The angle of the cutting face is also important, as is the flute width, number of flutes or teeth, and margin size. In order to have a long working life, all of the above must be optimized, plus the speeds and feeds at which the tool is run.
[edit] Types
Non-grinding cutting tools often can be classified as linear or rotary, depending on whether they rotate while cutting. Linear cutting tools include tool bits (single-point cutting tools) and broaches. Rotary cutting tools include drill bits, countersinks and counterbores, taps and dies, milling cutters, and reamers. Other cutting tools, such as band saw blades and fly cutters, combine aspects of linear and rotary motion.
As mentioned earlier, grinding wheels are also true cutting tools, although the terms are often not used that way.
[edit] Materials
Cutting tools (non-grinding) are generally made of tool steels (today most often high speed steels [HSS], whether conventional HSS grades or cobalt HSS), carbides, ceramics, or industrial diamonds.
Grinding wheels are usually made of abrasives such as aluminum oxide, silicon carbide, emery, or diamonds.
