A G-code test in a CNC interview is rarely about trick questions. It checks one thing: can you read a program and say what it does without reaching for the manual. That is recall, and it is exactly what you can practice in advance.
What they actually ask
Most beginner and operator interviews stay close to the codes you would meet in your first weeks:
- Read a short block. “What does
G01 X50 F150do?” (a straight feed move to X50 at 150 units per minute). - Code to meaning. “What is
G00?” (rapid positioning). - The common mix-ups.
G00vsG01, orG02vsG03. - Spindle and safety basics. What
M03andM05do, and why you stop the spindle before a tool change.
You will almost never be asked for an obscure canned cycle on the spot. The point is fluency with the basics.
The codes to know cold
| Code | Meaning | Why it comes up |
|---|---|---|
G00 / G01 | Rapid / linear feed | The two most common moves |
G02 / G03 | Clockwise / counterclockwise arc | Tests direction recall |
G20 / G21 | Inch / millimeter units | Easy to overlook, easy to test |
G90 / G91 | Absolute / incremental | Shows you understand modes |
M03 / M05 | Spindle on (CW) / stop | Spindle basics, safety habits |
If you can answer every row above instantly, in both directions, you are ready for the code portion of most interviews. The deeper breakdowns live in common G-codes for CNC beginners and common M-codes for CNC beginners.
How to prep in a week
Reading a cheat sheet builds recognition, not recall, so it falls apart under interview pressure. Drill retrieval instead: see a code, answer from memory, check, repeat. Spend extra reps on the pairs you confuse, like G00 vs G01. The full method is in beginner CNC code practice, and a timed mode (like the one in G-Code Sprint) is useful because it rehearses answering quickly, which is the part interviews actually test.
For worked examples, see CNC practical test examples for a job interview. If you are interviewing abroad, the same fundamentals apply, as covered in CNC operator jobs in Dubai test questions. And before you run anything on a real machine, understand how to safely test a program without crashing.
Bottom line
A CNC interview G-code test checks fluency with the common codes, not exotic ones. Drill the motion codes, units, positioning, and spindle basics with active recall and a timer, and the code questions become the easy part of the interview.
Sources
- NIMS (National Institute for Metalworking Skills)
- LinuxCNC G-code quick reference
- CNCCookbook: G-code and M-code cheat sheet
Frequently asked questions
What G-codes come up most in CNC interviews?
The motion codes G00, G01, G02, and G03, the spindle codes M03 and M05, units (G20/G21), and positioning (G90/G91). Interviewers want to see you can read a short program, not recite the whole standard.
How long should I study for a CNC interview test?
A few short sessions over a week is enough for most beginners if you use active recall. Cramming the night before fades fast; spaced drills stick.
What is the best way to prepare for a G-code interview test?
Drill the common codes with active recall instead of re-reading a chart. A free tool like G-Code Sprint has a timed mode that mimics interview pressure and a weak-code review that focuses on what you keep missing.
G-Code Sprint is a study and practice tool only. Always follow your instructor, employer, machine manual, and shop safety procedures.