CNC machinist technical exam – how deep do the G-code questions actually go on the written test?
I've been a CNC machinist for six years running mills and lathes, mostly Haas and Mazak machines, and I'm preparing for the CNC Computer Numerical Control Machinist Technical certification exam. My practical skills are solid but I'm honestly not sure how much the written exam focuses on G-code and M-code knowledge versus blueprint reading, metrology, and tooling selection. I want to make sure I'm not spending most of my study time on programming when the exam might care more about something else entirely.
I've been studying for about five weeks, maybe an hour to an hour and a half on most weeknights. My current practice scores are around 69%, which doesn't feel like enough. The blueprint reading and GD&T sections are fine — that's second nature from daily work. Where I'm struggling is with questions that feel more academic than practical, like theoretical cutting speed and feed calculations, tool geometry angles, and some safety standard questions that don't map cleanly to how things actually work on the shop floor.
I've talked to two guys at my shop who took the exam a couple years back. One said the G-code section was deeper than he expected and he wishes he'd reviewed canned cycles more thoroughly. The other said the programming questions were pretty basic and the metrology section was the real challenge. I don't know who to believe. If anyone's taken this recently I'd really appreciate a current read on what the exam actually emphasizes.
Your 69% with six years of shop experience is close to passing territory already — the gap is almost certainly the academic-style questions on theory and safety standards, not your practical knowledge. Find a question bank that emphasizes those areas and do two or three focused sessions on them. That's probably worth 8–10 percentage points by itself before your test date.
I took a similar CNC machinist certification about eighteen months ago and the G-code questions were moderate — not deep programming knowledge but you need to recognize what common codes do and be able to read a simple program and identify errors. Canned cycles like G81, G83, and G84 are worth reviewing. You don't need to write programs from scratch.
Metrology and inspection content was heavier than I expected on my exam. Understand how to read a micrometer and vernier caliper to tenths, know your gage R&R concepts at a basic level, and review common CMM terminology. That section rewards study time more than the G-code portion does for experienced machinists who already live in the code.
The speeds and feeds calculation questions are annoying if you're used to dialing things in by feel or trusting the software. Memorize the basic formulas for surface feet per minute and chip load — there were maybe four or five calculation questions and they're straightforward if you know the formula going in. Don't let them catch you unprepared.
So I was in a similar spot about eight months ago, working full-time on a Haas VF-2 and trying to squeeze in study time whenever I could. Honestly the G-code questions aren't as deep as I expected. They're not asking you to write a full program from scratch or anything like that. It's more like "what does G41 do" or "which code initiates a canned drilling cycle" -- recognizing codes rather than programming them. What tripped me up more was the coordinate system stuff, so I'd spend some time on cnc/questions/coordinate systems datum setup before your test date because that showed up more than I anticipated.
For fitting it in around a busy schedule, I didn't do long study sessions. I'd do 20-30 minutes on my lunch break or right after the kids went to bed. It's not glamorous but it adds up fast. The practical experience you already have is a huge advantage because a lot of the questions just click when you've actually run the machines.