What is a machinist: definition, duties and trade

Definition and role

A machinist is the person who shapes metal parts —or parts made of other hard materials such as certain technical plastics— by removing material from a raw workpiece until it has the exact geometry and dimensions called for by a drawing. That work of taking away material in the form of chips is known as machining by chip removal, and it is the essence of the trade: no material is added or melted, it is removed with precision until the desired dimension is reached.

The key word is precision. A machined part may need to meet tolerances of hundredths or even thousandths of a millimetre, because it will later be assembled together with other parts inside an engine, a gearbox or a landing gear. The machinist does not just "make holes": they guarantee that every measurement is within the tolerance the design allows. That is why the trade combines manual skill, knowledge of materials, technical reading and, increasingly, programming.

In Spanish vocational training, the reference figure is the Machining Technician, an Intermediate-level VET programme within the Mechanical Manufacturing professional family. Its general competence consists of manufacturing parts through machining processes, both with conventional machine tools and with numerical control machines, complying with quality, safety and environmental protection standards.

What a machinist does day to day

Although every workshop is different, a machinist's day usually revolves around a fairly recognisable sequence. It is not just pressing a button: there is a preparation phase and a quality control phase that are worth as much as the cutting itself.

• Interpreting drawings. Before touching the machine they read the part drawing: dimensions, tolerances, surface finishes, threads, machining symbols and references. The whole manufacturing strategy comes out of that reading.
• Setting up and programming the machine. They select the raw material, clamp it correctly (for example, in the lathe chuck or the milling machine vice) and, if working with CNC, write or review the machining program, today typically with CAM software or G-code.
• Adjusting the tools. They mount and set the cutting tools, fix the part origins, check spindle speeds and feed rates, and make corrections to compensate for tool wear.
• Machining the part. They start the process and watch the chip removal: noise, vibration, heat, coolant. A good machinist "listens" to the machine and detects before anyone else when something is going wrong.
• Checking the dimensions with metrology. Once the part is finished, they measure it with dimensional metrology instruments —vernier caliper, micrometer, dial gauge, gauges or even a coordinate measuring machine (CMM)— to confirm that everything is within tolerance. If it is not, they correct the process.

Types of machining

Under the umbrella of chip removal, several processes coexist. A machinist rarely masters just one; the norm is to combine them depending on the part. These are the most common:

Turning

The part rotates held in the spindle while a fixed tool removes material from it. It is the ideal process for parts of revolution: shafts, bushings, screws, pulleys. It is done on the lathe.

Milling

Here it is the tool that rotates (the milling cutter) while the part moves. It allows you to generate flat surfaces, slots, pockets, contours and complex shapes in three or more axes. It is done on the milling machine.

Drilling

It makes holes with a rotating drill bit. Although it may seem simple, controlling the position, diameter and perpendicularity of the hole is also part of the trade, and it is usually combined with reaming or threading.

Grinding

It uses an abrasive wheel to achieve very fine finishes and very tight tolerances, normally as a final step after other machining operations or a heat treatment.

Machines: lathe, milling machine and CNC

The two mother machines of the workshop are still the lathe and the milling machine. For decades they were operated manually, with handwheels and cranks, and those machines are called conventional. Today most of the work is done with computer numerical control (CNC): the machine runs a program that defines toolpaths, speeds and tool changes with a repeatability impossible to match by hand.

CNC has not eliminated the trade, it has shifted it. Today's machinist spends less time turning cranks and more time interpreting the drawing, generating the toolpath, simulating the program and controlling quality. Knowing conventional machines is still valuable —it teaches the fundamentals of cutting—, but mastering CNC is what opens up the best opportunities. If you want to go deeper into this, we have a guide dedicated to the CNC lathe and milling machine.

Difference between machinist, lathe operator, milling operator and fitter

These terms are often mixed up, but they do not mean exactly the same thing. The distinction has to do with specialisation:

• Machinist is the general term: someone who makes parts by chip removal and can handle several processes and machines. It is the figure trained by VET in Machining.
• Lathe operator is the specialist on the lathe. They master turning and parts of revolution.
• Milling operator is the specialist on the milling machine. Their terrain is flat surfaces, slots and contours.
• Fitter works on the manual assembly and fitting of parts: they file, scrape, check fits and assemble sets. Their focus is not so much removing chips on a machine as getting the parts to fit together with precision.

Put another way: lathe operators and milling operators are machinists specialised by type of machine, while the fitter deals mainly with assembly and fine fitting. In a small workshop, one and the same person may do everything; in large industry, the roles are more separated.

Sectors where a machinist works

Machining is cross-cutting: almost any product with precision metal parts passes, at some point, through a machining workshop. The three big destinations of the trade are:

• Metal and capital goods. Machining workshops, machinery manufacturing, moulds and dies, industrial maintenance. It is the historical foundation of the sector.
• Automotive. Engine, transmission, brake and chassis components, both for manufacturers and for the huge network of component suppliers.
• Aerospace. One of the most demanding sectors in terms of tolerances and traceability, with difficult materials such as titanium or superalloys. It tends to pay better precisely because of that demand.

From here, if the trade interests you, the natural next step is to see how to become a machinist and get a realistic idea of how much the sector pays.