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is an occupation
or a class of material-working processes
that involves using a power-driven machine tool
, such as a lathe
, milling machine or drill
, to shape metal
. Machining is a part of the manufacture of almost all metal products. Some plastic
parts are machined. A person who specializes in machining is called a machinist
A room, building, or company where machining is done is called a machine shop.
Most machining operations can be divided into those that remove metal from an item, and those that form metal in an item.
Often an unfinished workpiece will need to have some parts removed or scraped away in order to create a finished product. For example, a lathe is a machine tool that generates circular sections by rotating a metal workpiece, so that a cutting tool can peel metal off, creating a smooth, round surface. A drill or punch press can be used to remove metal in the shape of a hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding tools. Many of these same techniques are used in woodworking.
Metal can be formed into a desired shape much more easily than materials such as wood or stone, especially when the metal is heated. A machinist may use a forging machine to hammer or mold a hot metal workpiece into a desired shape. Dies or molds may be used if the metal is soft enough, or under high pressures. A press is used to flatten a piece of metal into a desired shape.
Advanced machining operations might use electrical discharge (EDM), elecro-chemical erosion, plasma arc cutters or laser water jet cutting to shape metal workpieces.
As a commercial venture, machining is generally performed in a machine shop, which consists of one or more workrooms containing major machine tools. Although a machine shop can be a stand alone operation, many businesses maintain internal machine shops which support specialized needs of the business.
The inferior finish found on the machined surface of a workpiece may be caused by insufficient clamping, cutting conditions (speed) or perhaps an incorrectly adjusted tool. It is evident by an undulating or irregular finish, and the appearance of waves on the surface.
Machining as a hobby
Machining can be a hobby in itself, or it can be useful in pursuing other hobbies. For instance, plenty of car restorers have home workshops with a range of machine tools. There are also individuals who start building up a home workshop with the idea of eventually building some project, such as maybe a miniature steam locomotive, but get sidetracked into building the machine tools themselves and their accessories. The home machine shop thus may end up being a satisfying hobby in itself. There are in fact at least four magazines that cater to this side of the hobby, "Home Shop Machinist" and "Machinist's Workshop" in the USA, and "Model Engineer" and "Model Engineer's Workshop" in the United Kingdom. "Machinist's Workshop" and "Model Engineer's Workshop" tend to be very project-oriented, while the other two tend to present a mix of projects, techniques, and theory.