E Is for End Mill

Metalworking Glossary for the Letter E

See the index to the Glossaries here:


  • Eccentric. Also called off-center, it is a circle that does not have a geometric center. The term eccentric also applies to a device such as a crankshaft or a cam for converting rotary motion to reciprocating motion.
  • EDM. Abbreviation for electrical discharge machine, a device that uses electrical discharges in the form of sparks to cut through a metal workpiece.
  • Effective Rake Angle. The combination of the back rake angle and the side rake angle of a cutting tool. Also known as true rake angle or resultant rake angle.
  • Elastic Limit. The maximum amount of stress that can be applied to a metal or other material without any strain remaining in it when the stress is removed.
  • Elasticity. A metal’s elasticity is a measure of the rate at which it can be distorted under stress and still return to its original shape without deformation.
  • Electric Press Brake. A powered press brake that is equipped with servomotors instead of hydraulic cylinders. Accurate and energy-efficient machines, electric brakes also run much quieter than other types of press brakes.
  • Electrical Discharge Machine. Any machine that uses the electric spark erosion principle is considered an electrical discharge machine, though the two most common types are the conventional and wire EDM machines.
  • Elongation. The amount of permanent stretch that can be put into piece of metal before rupture. The percentage of elongation is an indication of ductility.
  • Emery. A dark granular rock (also called corundite) that is used to make a natural abrasive powder for grinding or polishing.
  • Emulsion. A coolant formed by mixing water with soluble oils or compounds.
  • End Mill. The most common type of cutting tools employed in milling processes on vertical mills, end mills are sharpened on the sides and not just the end, allowing them to cut material in different directions and be used in a variety of different machining operations.
  • End Milling. A type of milling operation in which a narrow cutter is used to machine surfaces in both downward and sideways directions. The type of cutting tool used is called an end mill, and the most typical style looks like a drill bit, but with cutting surfaces on its tip as well as around its circumference so that it can mill in multiple directions. End milling is an extremely versatile operation and can be used for machining slots, holes, contours, profiles, shoulders, fins, and other shapes in a workpiece.
  • Engine Lathe. An engine lathe is the standard lathe used from the late 19th century through the 20th and into the 21st. The term “engine” as used here simply means that it is a mechanical device, not an indication of a power source. It is distinguished from the lathes that came before with their hand-held tools by its use of a mounted cutting tool with an automatic feed.
  • Engineer’s Spirit Level. A longer term for a level, a tool used to check the levelness of a surface using an imbedded bubble gauge.
  • Engineer’s Square. Another name for a machinist square, a device for confirming right angles.
  • External Micrometer. A micrometer used to measure the outside diameter of a circular object.
  • Extrusion. As a noun, it is a part shaped by forcing material through a die opening. As a verb, extrusion refers to the process of shaping metal into a specific continuous form by forcing it to flow through a die orifice. Metals such as aluminum, copper, lead, tin, and zinc can be formed by being extruded.