Machining Has Evolved with Technology
Over the past 150 years the precise meaning of the term machining has evolved as technology has advanced. In the 18th century, the word machinist simply meant a person who built, or repaired machines. This person’s work was done mostly by hand, using processes such as the carving of wood and the hand forging and hand filing of metal. At the time, millwrights and builders of new kinds of engines (meaning, more or less, machines of any kind), such as James Watt or John Wilkinson, would fit the definition.
New Wording Attached to Machining
The noun machine tool and the verb to machine (machined, machining) did not yet exist in the early days. Those words were coined as the concepts that they described evolved into widespread existence. Therefore, during the Machine Age, machining referred to (what we today might call) the “traditional” machining processes, such as turning, boring, drilling, milling, broaching, sawing, shaping, planning, reaming and tapping. In these “traditional” or “conventional” machining processes, machine tools, such as lathes, milling machines, drill presses or others, are used with a sharp cutting tool to remove material to achieve a desired geometry.
Current Principal Machining Processes
The three principal machining processes today are classified as turning, drilling and milling. Other operations falling into miscellaneous categories include shaping, planning, boring, broaching and sawing. Turning operations are operations that rotate the work piece as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning. Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the work piece. Milling machines are the principal machine tool used in milling. Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the work piece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills. Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be swarf producing operations but these operations are performed at a typical machine tool. Burnishing is an example of a miscellaneous operation. Burnishing produces no swarf but can be performed at a lathe, mill, or drill press.
Machining Essential to Unfinished Work piece
An unfinished work piece requiring machining will need to have some material cut away to create a finished product. A finished product would be a work piece that meets the specifications set out for that work piece by engineering drawings or blueprints. For example, a work piece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal work piece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and grinding machines. Many of these same techniques are used in woodworking.
Recent Advanced Machining Techniques
More recent, advanced machining techniques include electrical discharge machining (EDM), electro-chemical erosion, laser cutting or water jet cutting to shape metal work pieces.
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. Machining requires attention to many details for a work piece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the work piece. The inferior finish found on the machined surface of a work piece may be caused by incorrect clamping, a dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the work piece.