What does a CNC machinist do? From setup to precision inspection

What CNC machinists make and how they work

A casting, forging or welded assembly arrives at the machine with material still to remove. The drawing specifies the bores, surfaces and tolerances it needs. The CNC machinist plans the setup, selects the tools and programs the operations that turn this blank into a finished component.

Machining removes material as chips. Turning, milling and drilling each use this principle to produce a different geometry. Because excess material cannot simply be put back, the cutting sequence and the dimensions need careful checking.

Before the spindle starts, the machinist decides how to support and clamp the part, which reference surfaces to use and which tools and cutting data suit the material. The CNC control executes the program; the machinist plans the process and checks the result.

At Bock, this work includes machine beds, press frames, housings and large rings. Their scale makes setup planning especially important. Examples are shown on the CNC large-part machining page.

Daily tasks: setup, programming, tool selection and inspection

The cutting cycle is one part of the job. A typical order also involves planning, setup, programming and inspection:

• Setting up: the component is clamped, aligned and probed. For a part that weighs several tonnes, this is not a quick task but a piece of planning – including the crane, the clamping equipment and the question of where it may be clamped without anything distorting.
• Programming and adjusting: CNC programs are written to the drawing and fine-tuned at the machine. With one-off parts, no proven program ever runs a second time – each one is written for exactly this component.
• Choosing and managing tools: cutting material, cutting speed, feed, depth of cut. The same milling cutter behaves differently in structural steel than in stainless steel – and a wrongly chosen tool costs not only tool life but, in the worst case, the component.
• Monitoring the first cut: watching the tool engagement, chip formation and spindle load, and listening for changes in the cut. These observations help identify problems early.
• Measuring and documenting: dimensional inspection on the workpiece, often while it is still in the setup. Only the inspection record turns a finished part into an accepted one.

Preparation gives the machining cycle a reliable starting point. Monitoring and measurement then confirm that the planned process is producing the required result.

CNC machining, industrial mechanics or toolmaking: how the roles differ

Three metalworking trades that are often lumped together. The difference lies in what you hold in your hand at the end:

Rule of thumb: the Werkzeugmechaniker builds the tool, the Zerspanungsmechaniker uses it, and the Industriemechaniker keeps the machine that holds both running.

Large-part machining: why setup matters so much

In series production, setup and programming are spread across many identical parts. In one-off and small-batch work, those decisions have to be made for each new component. With large parts, getting the setup right can matter more than reducing the cutting cycle by a few seconds.

The machines set the scale. The larger of the two Zayer Thera W offers 26,000 mm of travel and a table clamping surface of 26,500 × 4,000 mm, the smaller one 16,000 mm and 16,500 × 3,000 mm; both are controlled by Heidenhain iTNC. Added to these are the Soraluce FR 20000 travelling-column milling centre and three TOS-Varnsdorf WHN 13 CNC horizontal boring mills. Turning is done, among others, on the Feichter FKD30/20 vertical lathe up to Ø 4,800 mm – and with driven tools, milling and drilling too, in a single setup.

For the trade, this means something very concrete: a component of 50 t is not simply re-clamped. Every additional setup costs hours, needs the crane and brings a new reference surface into the dimensional chain. That is why a machinist here thinks longer before starting – and has to re-mill less often afterwards.

By the time a welded component reaches machining, it may already contain weeks of cutting, fabrication and stress-relief work. Checking the clamping, tool path and work offset protects that investment and helps prevent avoidable scrap.

All machines in the machine park

German job titles: turner, milling machinist and machining technician

Many names are in circulation for the same trade. Some are older than the trade itself, some come from Austria or the GDR, and one is a further qualification. What lies behind each of them:

Rule of thumb: in Germany the apprenticeship trade in industry is called Zerspanungsmechaniker, in the skilled crafts Feinwerkmechaniker. You only become a “Techniker” afterwards, through a further qualification – the routes available are described in the chapter After the apprenticeship.

The German apprenticeship: from manual machining to CNC programming

The apprenticeship takes three and a half years, alternating between the company and vocational school (dual vocational training). The ordinance sets out a common trade profile, and the training company also defines one of four areas of deployment: automatic lathe, lathe, milling machine or grinding machine systems. Here a similar line runs through the workshop – milling and boring on gantry milling machines, the travelling column and boring mills is one work area, turning on the vertical lathe another. The order of the apprenticeship is deliberately old-fashioned – CNC comes last:

• By hand first: on the conventional lathe you develop a feel for chip, spindle speed and feed. Anyone who only knows CNC cannot judge later whether a value is plausible.
• Reading drawings: dimensions, tolerances, geometric tolerancing symbols, surface specifications. Without this, a CNC program is merely typed in.
• Learning to set up: clamping, aligning, setting the zero point – first on manageable parts, later on the large ones.
• Programming under guidance: first programs of your own on Heidenhain and Siemens controls, initially on simple contours.
• Inspecting: vernier caliper, micrometer, dial gauge, probing systems. Self-inspection is part of it from the very beginning.

Apprentices work on components for customer orders, with guidance from experienced colleagues. As their skills develop, they take on more responsibility for setup, machining and checking their own work.

To the apprenticeship page at Bock

The two-part final examination: 40% and 60% of the grade

In Germany, the former intermediate examination was replaced in 2007 by a final examination held in two parts at different stages of training. Both parts count towards the overall result.

• Part 1, before the end of the second year of the apprenticeship: a production assignment in turning-milling, turning-grinding or milling-grinding technology, at most eight hours including written tasks. It counts for 40 per cent of the overall grade.
• Part 2, at the end of the apprenticeship, counts for 60 per cent. Half of it is the work assignment – either an order from the company itself or a practical work task, each with a technical discussion. Which variant applies is chosen by the training company.
• Written papers in Part 2: order and function analysis and production technology at 20 per cent each, economics and social studies at 10 per cent.
• Since 1 August 2018, additional qualifications can be agreed: system integration, process integration, additive manufacturing processes and IT-supported plant modification. On application, they are examined as a separate examination within Part 2.

In practice this means: Part 1 is not a dress rehearsal. Anyone who sits the examination after two years already fixes two fifths of their grade there – and the production assignment demands exactly what the apprenticeship above builds up in this order: evaluating documents, planning the sequence, producing, inspecting and documenting.

Before and after machining: the production chain at Bock

A machinist never works on their machine alone – they work on what others have done before. At Bock, these steps are under one roof on 14,000 m²:

• Before machining: cutting, forming and the welded structure to DIN EN 1090-2 EXC3. Anyone who sees their blank being made knows where the allowances are and what to expect.
• Stress relieving: vibration stress relief before machining, so that the component does not move only after milling. That is the difference between a dimension and a dimension that holds.
• Materials from our own stock, over 40 grades with inspection certificate 3.1 to EN 10204 – from structural steel through wear-resistant steel to stainless steel. Each one requires different cutting data.
• After machining: shot blasting, painting and assembly. Anyone who knows what comes next understands why a mating surface has to be protected.
• Crane logistics up to 25 t: with components of this size, slinging is part of the trade, not a side job.

In everyday work, this proximity is a tangible advantage: if something about a component is unclear, the colleague who welded it is two halls away – and not at a supplier you have to call.

What to consider before becoming a CNC machinist

CNC machining combines numerical work, careful organisation and responsibility for valuable components. The main demands are:

• Practical maths: spindle speed, feed, depth of cut and tolerance limits involve calculations every day. The methods can be learned; applying them carefully is part of the job.
• Patience during long cycles: roughing a large component can take hours. Setup, monitoring and inspection remain important even when progress is gradual.
• Responsibility for the workpiece: a part may already contain weeks of other people’s work. Checking the setup and program helps protect it before cutting begins.
• An organised approach: tools, work offsets and inspection records must be kept in order so that the process remains reliable and traceable.
• An interest in precision machining: the focus is on producing dimensions and surfaces. Those who prefer assembling structures from separate parts may want to explore structural metal fitting, the Konstruktionsmechaniker trade.

Career paths and further qualifications

The final apprenticeship examination marks the start of a skilled career. As experience grows, machinists take on more demanding components and greater responsibility for the setup and machining sequence.

Formally, three further qualifications lead onwards: to Geprüfter Industriemeister, Fachrichtung Metall (certified industrial master craftsman, metal), to Geprüfter Technischer Fachwirt (certified technical business administrator) – both via the IHK (Chamber of Industry and Commerce) – and to Staatlich geprüfter Techniker at a Fachschule (technical college), for example in mechanical engineering or machining technology. The Techniker is also what lies behind “Zerspanungstechniker” in Germany: a qualification after the apprenticeship, not a substitute for it.

Then there is the range of machines. Anyone who can operate gantry milling machines, the travelling column, the boring mill and the vertical lathe is a different kind of partner in process planning from someone who knows one machine. And the neighbouring trades are in the same building: welding to DIN EN 1090-2 EXC3, non-destructive testing by personnel qualified to ISO 9712, surface technology.

What ends up on the payslip depends on concrete things: on the machines someone runs confidently, on the responsibility in setting up and on whether a program is written by oneself or merely run. That is why we do not quote a flat figure – pay depends on qualification, professional experience, area of work and individual agreement. Regardless of that, the same benefits apply to everyone in the company, from the company pension scheme to the travel allowance; they are listed on the page Careers at Bock, in a family business with 63 years of manufacturing experience.

Open positions and apprenticeship places