Machining is the process of creating or changing parts that are made primarily of metal, and less frequently, of plastic or wood. It may be accomplished by cutting, grinding, drilling, lathing, polishing and other technological processes that are performed to remove excess metal and shape the part. Machinists are individuals who use machinery tools to fabricate parts according to the parameters specified in blueprints, also known as technical drawings. They generally work with materials such as steel, brass, aluminium, copper and sometimes glass, plastic or wood. Machinists have to be proficient in using various machinery equipment because the making of a part frequently requires more than one technological process and tool. Most machinery tools are electrically powered equipment, but several hand tools may also be used occasionally. Machinists are essential workers in industries or fields where replacement parts are frequently needed, especially in emergency situations when the operation of equipment depends on the availability of a specific part.