CNC Machinist Interview Questions UK: 8 Real Questions and What Interviewers Want

Before your CNC Machinist interview, it helps to see the questions from the interviewer's side. We have picked eight from our set of 25 and added the reason each one gets asked.

Eight CNC Machinist interview questions, and what the interviewer is thinking

1. Which CNC controls and programming languages have you worked with, and how comfortable are you with G-code and M-code?

Why they ask: They need to know whether you can work with their machines and edit programs at the control without help.

2. How do you set up a CNC machine for a new job, from reading the drawing to running the first-off?

Why they ask: Setup is the core skill, and the interviewer wants to see a methodical approach that prevents scrap and crashes.

3. How do you calculate spindle speed and feed rate for a milling or turning operation?

Why they ask: It shows whether you understand cutting theory rather than just copying numbers.

4. How do you read an engineering drawing, and what is the difference between first angle and third angle projection?

Why they ask: Drawing interpretation is fundamental, and misreading one means scrapped parts.

5. Which measuring instruments do you use to inspect machined parts, and how do you make sure they are accurate?

Why they ask: Quality depends on correct measurement, so they check your instruments knowledge and discipline.

6. Your first-off part is a little outside tolerance on one dimension. What do you do?

Why they ask: They want to see problem-solving, correct use of offsets and discipline about quality.

7. Tell me about a time you machined a part with very tight tolerances or a difficult material.

Why they ask: They want to see real experience of precision work and how you solved problems.

8. What does a typical day for a CNC machinist involve?

Why they ask: They want to see whether you understand the realities of the job.

A sample answer to question 1

Which CNC controls and programming languages have you worked with, and how comfortable are you with G-code and M-code?

I've mainly used Fanuc and Siemens controls, and I've done some work on Heidenhain and Haas. I'm comfortable reading and editing G-code at the machine. For example, G00 for rapid moves, G01 for linear feed, G02 and G03 for arcs, G90 and G91 for absolute and incremental, G54 to G59 for work offsets, G40 to G42 for cutter compensation and G43 for tool length offsets. On the M-code side, M03 and M04 for spindle direction, M05 stop, M06 tool change, M08 and M09 for coolant, and M30 for program end. I can write simple programs manually, including canned cycles like G81 drilling and G83 peck drilling, and I use CAM-generated programs from systems such as Mastercam. I always read through the program and check the tool list, offsets and starting conditions before running anything.

Common mistake to avoid: Naming codes without knowing the function; Claiming every control

Want the rest?

Full model answers, key points and common mistakes for all 25 questions are on the CNC Machinist interview questions page. The first five are free, no sign-up needed.