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End mill

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End mill

An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. They can have several end configurations: round (ball), tapered, or straight are a few popular types. They are most commonly used in "milling machines" that move a piece of material against the end mill to remove chips of the material to create a desired size or shape. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most milling bits can cut in the radial direction. Not all mills can cut tangentially: those designed to do so are known as end mills.

End mills are used in milling applications such as profile milling, tracer milling, face milling, and plunging.

Several broad categories of end- and face-milling tools exist, such as center-cutting versus non-center-cutting (whether the mill can take plunging cuts); and categorization by number of flutes; by helix angle; by material; and by coating material. Each category may be further divided by specific application and special geometry. Additional milling application categories include, woodworking, automotive manufacturing and customization, and all types of machining.

A very popular helix angle, especially for general cutting of metal materials, is 30°. For finishing end mills, it is common to see more tight spiral, with helix angles 45° or 60°. Straight flute end mills (helix angle 0°) are used in special applications, like milling plastics or composites of epoxy and glass. Straight flute end mills were also used historically for metal cutting before invention of helical flute end mill by Carl A. Bergstrom of Weldon Tool Company in 1918.

There exist end mills with variable flute helix or pseudo-random helix angle, and discontinuous flute geometries, to help break material into smaller pieces while cutting (improving chip evacuation and reducing risk of jamming) and reduce tool engagement on big cuts. Some modern designs also include small features like the corner chamfer and chipbreaker. While more expensive, due to more complex design and manufacturing process, such end mills can last longer due to less wear and improve productivity in high speed machining (HSM) applications.

It is becoming increasingly common for traditional solid end mills to be replaced by more cost-effective inserted cutting tools (which, though more expensive initially, reduce tool-change times and allow for the easy replacement of worn or broken cutting edges rather than the entire tool). Another advantage of indexable end mills(another term for tools with inserts) is their ability to be flexible with what materials they can work on, rather than being specialized for a certain material type like more traditional end mills. For the time being however, this only generally applies to larger diameter end mills, at or above 3/4 of an inch. These end mills are generally used for roughing operation, whereas traditional end mills are still used for finishing and work where a smaller diameter, or a tighter tolerance, are required; modular tooling introduces additional margins of error that can compound with each new component, whereas a solid tool can provide a smaller tolerance range for the same price level.

End mills are sold in both imperial and metric shank and cutting diameters. In the USA, metric is readily available, but it is only used in some machine shops and not others; in Canada, due to the country's proximity to the US, much the same is true. In Asia and Europe, metric diameters are standard.[citation needed]

A variety of grooves, slots, and pockets in the work-piece may be produced from a variety of tool bits. Common tool bit types are: square end cutters, ball end cutters, t-slot cutters, and shell mills. Square end cutters can mill square slots, pockets, and edges. Ball end cutters mill radiused slots or fillets. T-slot cutters mill exactly that: T-shaped slots. Shell end cutters are used for large flat surfaces and for angle cuts. There are variations of these tool types as well.

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