An endmill is a type of milling cutter

Milling cutter

Milling cutters are cutting tools typically used in milling machines or machining centres . They remove material by their movement within the machine or directly from the cutter's shape .-Features of a milling cutter:Milling cutters come in several shapes and many sizes...

, a cutting tool

Cutting

Cutting is the separation of a physical object, or a portion of a physical object, into two portions, through the application of an acutely directed force. An implement commonly used for cutting is the knife or in medical cases the scalpel...

 used in industrial milling

Milling machine

A milling machine is a machine tool used to machine solid materials. Milling machines are often classed in two basic forms, horizontal and vertical, which refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines...

 applications. It is distinguished from the drill bit

Drill bit

Drill bits are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides torque and axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes....

, in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, a milling bit can generally cut in all directions, though some cannot cut axially.

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

Types

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.

It is becoming increasingly common for traditional solid endmills to be replaced by more cost-effective inserted cutting tools

Tipped tool

A tipped tool generally refers to any cutting tool where the cutting edge consists of a separate piece of material, either brazed, welded or clamped on to a separate body. Common materials for tips include tungsten carbide, polycrystalline diamond, and cubic boron nitride...

 (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).

Endmills 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, while imperial is readily available, metric diameters are standard.

Geometry and tools

A variety of grooves, slots, and pockets in the workpiece 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.

There are four critical angles of each cutting tool: end cutting edge angle, axial relief angle, radial relief angle, and radial rake angle

Rake angle

Rake angle is a parameter used in various cutting and machining processes, describing the angle of the cutting face relative to the work. There are three types of rake angles: positive, negative, and zero...

. See graph for common values.

Depending on the material being milled, and what task should be performed, different tool types and geometry may be used. For instance, when milling a material like aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, it may be advantageous to use a tool with very deep, polished flutes and a very sharp cutting edge. When machining a tough material such as stainless steel

Stainless steel

In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....

, however, shallow flutes and a squared-off cutting edge will optimize material removal and tool life.

A wide variety of materials are used to produce the cutting tools. Carbide inserts are the most common because they are good for high production milling. High speed steel is commonly used when a special tool shape is needed, not usually used for high production processes. Ceramics inserts are typically used in high speed machining with high production. Diamond inserts are typically used on products that require tight tolerances, typically consisting of high surface qualities (nonferrous or nonmetallic materials). In the early 1990s, use of coatings to reduce wear and friction (among other things) became more common. Most of these coatings are referred to by their chemical composition, such as:

• TiN
  Titanium nitride
  Titanium nitride is an extremely hard ceramic material, often used as a coating on titanium alloys, steel, carbide, and aluminium components to improve the substrate's surface properties....
  
   (a basic yellowish coating that has fallen out of wide use)
• TiCN (a popular bluish-grey coating)
• TiAlN and AlTiN
  Titanium aluminium nitride
  Titanium aluminium nitride or aluminium titanium nitride stands for a group of metastable hard coatings consisting of the metallic elements aluminium, titanium and nitrogen...
  
   (an extremely popular dark purple coating)
• TiAlCrN, AlTiCrN and AlCrTiN (PVD coating).
• PCD veins. Though not a coating some endmills are manufactured with a 'vein' of polycrystaline diamond. The vein is formed in a high temperature-high pressure environment. The vein is formed in a blank and then the material is ground out along the vein to form the cutting edge. The tools can be very costly, however can last many times longer than other tooling.

Advances in endmill coatings are being made, however, with coatings such as Amorphous Diamond and nanocomposite PVD coatings beginning to be seen at high-end shops (as of 2004).

Manufacture

Endmills are typically made on CNC (Computer Numeric Control) controlled Tool and cutter grinder

Tool and Cutter grinder

A tool and cutter grinder is used to sharpen milling cutters and tool bits along with a host of other cutting tools.It is an extremely versatile machine used to perform a variety of grinding operations: surface, cylindrical, or complex shapes...

 machines under high-pressure lubricants

Cutting fluid

Cutting fluid is a type of coolant and lubricant designed specifically for metalworking and machining processes. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols , and air or other gases. They may be made from petroleum distillates, animal...

 such as water, water-soluble oil, and high-flashpoint oil. Grinding inside the machine is accomplished with abrasive wheels

Grinding wheel

A grinding wheel is an expendable wheel that is composed of an abrasive compound used for various grinding and abrasive machining operations...

mounted on a spindle (and in some cases, multiple spindles). Depending on what material is being ground, these wheels are made with industrial diamond (when grinding tungsten carbide), cubic boron nitride (when grinding cobalt steel), and other materials (when grinding, for instance, ceramics), set in a bond (sometimes copper).