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CNC Machinist interview questions and how to answer them

A machinist interview is half conversation and half proof. The shop lead wants to hear how you think through a setup, and then they'll often hand you a print or a micrometer to see if your hands match your words. Plan for both.

12 questions7 minute read

Part 1

1.Walk me through how you set up a new job on a CNC mill.

Why they ask

This is the core of the job. They want to know if you can take a job from print to first good part without someone standing over you.

How to answer

  • Start with the print and the setup sheet: material, workholding, tool list
  • Mount and indicate the vise or fixture, then set the work offset with an edge finder or probe
  • Load tools and touch off tool lengths, checking them against the tool list
  • Run the first part in single block with rapids and feeds turned down
  • Measure the first part fully and adjust offsets before running production

2.What's the difference between a work offset and a tool length offset?

Why they ask

Mixing these up is the fastest way to crash a machine. It's a quick filter for whether you've really done setups.

How to answer

  • Work offset tells the machine where the part zero is, such as the first fixture offset on the control
  • Tool length offset tells it how far each tool sticks out from the spindle
  • Give an example of adjusting one to fix a dimension
  • Mention checking offsets after a tool change or a new fixture

3.Your parts start drifting out of tolerance halfway through a run. What do you do?

Why they ask

Drift happens on every long run. They want someone who catches it early and finds the cause instead of chasing it with offsets forever.

How to answer

  • Stop and quarantine the suspect parts so nothing bad ships
  • Check the obvious causes: tool wear, a chipped insert, loose workholding, chip buildup
  • Think about heat: machine warm-up and coolant temperature can move a dimension
  • Adjust the wear offset or change the tool, then measure the next few parts closely
  • Log what happened so the next shift knows
4.Tell me about a crash you had or almost had.

Why they ask

Everyone who's run machines long enough has a close call. They want honesty and proof that you learned from it.

How to answer

  • Describe what happened plainly, without blaming the programmer or the last shift
  • Name the cause: a wrong offset, a missed tool, a clamp in the path
  • Say what you did right after: feed hold, E-stop, reporting it
  • Explain the habit you changed afterward
5.How comfortable are you reading G-code and editing at the control?

Why they ask

Shops program in CAM, but the machinist is the last check before metal gets cut. They need you to catch mistakes and make small edits safely.

How to answer

  • Say which controls you've used, such as Fanuc, Haas, Mazak, or Okuma
  • Give an example of a program error you caught before running it
  • Describe the kinds of edits you make: feeds, speeds, a depth of cut
  • Mention how you document edits so the program stays in sync with CAM

Part 2

6.Here's a print. Tell me what this callout means.

Why they ask

Reading GD&T and tolerances is non-negotiable. A lot of shops test this directly with one of their own prints.

How to answer

  • Read the feature control frame out loud: the symbol, the tolerance, the datums
  • Say how you'd check it: height gauge, indicator, CMM, pins
  • Point out the tightest features and the ones that need a first-article check
  • Ask about anything unclear instead of guessing
7.Which measuring tools do you use, and how do you know they're right?

Why they ask

A good part measured with a bad micrometer is still a bad part. They want to see that you trust your gauges for a reason.

How to answer

  • List the tools you use every day: calipers, micrometers, bore gauges, thread gauges, indicators
  • Mention checking zero on a micrometer with a standard before measuring
  • Talk about calibration stickers and pulling a gauge that's out of date
  • Know when a part needs to go to the CMM or the inspection room
8.How do you pick feeds and speeds for a material you haven't cut before?

Why they ask

They're checking whether you use judgment and references, or just copy the last job.

How to answer

  • Start from the tooling manufacturer's recommended data
  • Adjust for the machine's rigidity, the workholding, and tool stickout
  • Start conservative and listen and watch the chips
  • Mention material quirks, like stainless work-hardening or aluminum building up on the edge
9.Tell me about a time you disagreed with how a job was programmed.

Why they ask

Machinists and programmers clash. They want someone who speaks up without starting a feud.

How to answer

  • Describe the problem you saw, like a bad toolpath or a weak fixture plan
  • Explain how you raised it with the programmer directly
  • Share what changed and how the part came out
  • Keep the tone respectful toward the other person
10.What does a good handoff to the next shift look like?

Why they ask

Many shops run around the clock. Bad handoffs cause scrap and crashes.

How to answer

  • Note where the run stands and the last good measurement
  • Flag worn tools, offset changes, and anything odd you noticed
  • Leave the machine and the area clean and ready
  • Talk face to face when you can, not just a note on the control

Part 3

11.How do you stay safe around the machines?

Why they ask

Injuries and crashes cost the shop money and people. They want habits, not slogans.

How to answer

  • Doors closed during the cycle, no reaching in while the spindle turns
  • Safety glasses, no gloves near rotating parts, loose sleeves rolled up
  • Lockout and tagout before any maintenance work
  • Knowing where the E-stop is and using feed hold early
12.Why do you want to work in this shop?

Why they ask

They want to know you looked at what they make and that you're likely to stay.

How to answer

  • Name the kind of work they do: aerospace, medical, oil field, job shop, production
  • Connect it to the machines or parts you want to learn
  • Mention the shift and that you can commit to it

Questions to ask them

Ask at least two. It shows you're picking them too.

  • Which machines and controls would I be running, and who does the setups on my shift?
  • How do you train someone to move from running parts to doing their own setups?
  • Who programs the jobs, and how do machinists give feedback on a program?
  • What does first-article inspection look like here, and do machinists run the CMM?
  • What's the scrap and rework process when a part comes out wrong?

Related interview guides

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