M Is for Machining

Metalworking Glossary for the Letter M

See the index to the Glossaries here:


  • Machinability. The characteristic of a metal or other material showing the relative ease of machining it to produce a satisfactory surface finish.
  • Machine Tool. A power-driven machine designed to bore, cut, drill, or grind metal or other materials. A machine tool always removes pieces of the material in the form of chips, though sometimes metal fabrication machines that bend or otherwise form metal will be lumped into the category of machine tool. The act of using a machine tool is called machining and a person who is skilled in the operation of various machine tools is called a machinist.
  • Machining. Using a machine tool to shape metal by removing small pieces from it (called chips or swarf).
  • Machining Center. An advanced type of CNC mill that is usually enclosed and is equipped with an automatic tool changer (ATC).
  • Machinist Square. Also known as an engineer’s square—or just simply “square”—a machinist square is used to confirm right angles.
  • Machinist’s Level. A longer term for a level, a tool used to check the levelness of a surface using an imbedded bubble gauge.
  • Magnesium. A ductile metal that is one-third less dense than aluminum. When alloyed with aluminum, magnesium improves the strain hardening ability and increases the strength of the metal, making it more ideal for fabrication and welding than pure aluminum. Magnesium is also added to molten iron and steel to remove sulfur.
  • Magnetic Chuck. A flat workholding device that uses magnetism to secure a ferrous metal part in place. Often found on surface grinders, some types of magnetic chucks are designed for use with milling, drilling, grooving, and other operations.
  • Magnetic Drill. Often called a “mag drill” for short, a magnetic drill is a portable drill press with a magnetic base that can be attached directly to a large or heavy workpiece that can’t easily be brought into a shop, such as a steel beam or the side of a ship. They are usually equipped with annular cutters that cut a groove at the outside of the hole, leaving a solid core or slug at the center.
  • Main Spindle. The main spindle of a lathe is the revolving shaft that holds and drives the workpiece or the cutting tool.
  • Malleable. A characteristic of a metal that means it is capable of being shaped, extended, or otherwise formed by hammering, rolling, or another fabrication process.
  • Mandrel. An arbor, cylinder, or blunt-ended tool used to retain or enlarge a cavity in a hollow piece of metal.
  • Manual Milling Machine. Any mill that is run by hand—instead of a control like a CNC—is called a manual mill.
  • Manufacturing Type Milling Machine. Another name for a bed type mill.
  • Mechanical Press Brake. The original type of powered press brakes are mechanical brakes. They use a flywheel and clutch mechanism to mechanically transfer energy to cycle the ram, but don’t have the precision of modern hydraulic and electric brakes.
  • Metal Lathe. A metal lathe is simply a lathe that is intended for metalworking as opposed to woodworking. Metal lathes, however, can also be used successfully with many plastics and other composite.
  • Metrology. The science of measurement, derived from the Greek words “metron,” meaning measurement, and “logos,” denoting a subject of study. By defining standard units of measurement, metrology can be used to validate and verify specifications against those units. In metalworking, metrology is employed by machinists and fabricators to check produced parts for accuracy by using precision inspection instruments. 
  • Micro Lathe. Another name for a mini lathe.
  • Micrometer. A micrometer is a precision measuring tool that is generally more accurate than a vernier caliper. An outside micrometer, also known as an external micrometer, often resembles a C-clamp and can measure the outside diameter of a circular object. An inside micrometer is used to measure the internal diameters of holes, such as hollow pipe. Micrometers can be analog or digital.
  • Mild Steel. A term commonly used for low-carbon (less than 3%) machine steel. Its malleability makes it easy to fabricate, machine, cut and weld.
  • Mill. Short for “milling machine,” a mill is a metalworking machine tool that engages a rotating cutting tool with a workpiece to remove material and shape it.
  • Mill Drill. A hybrid machine, a mill drill is a drill press that has a rigid table with X/Y coordinate movement like a mill to allow some light machining. The spindle of a mill drill is designed to accommodate the stresses of moving sideways while machining the workpiece.
  • Mill Scale. The heavy oxide layer that forms on steel during forging and other extreme heating.
  • Milling. In metalworking, the term milling refers to a type of machining process. Unlike a lathe, where a workpiece is rotated at a high speed and a cutting tool is slowly applied to the surface, milling machines (often called “mills” for short) will apply high speed, multi-point rotary cutters to a stationary workpiece to remove material.
  • Mini Lathe. A mini lathe is a small and affordable lathe designed for home workshops and small maintenance shops.
  • Morse Taper. Invented by machinist Charles A. Morse in the 1860s, the Morse taper was adopted as a standard system for attaching tools like end mills and drill bits to spindles during machining operations. Morse tapers fit both antique and modern drill presses.
  • Multi-spindle Lathe. A multi-spindle lathe is one that, as its name implies, has multiple spindles that are controlled automatically through cams or CNC. It is used for high-volume production.