Why pre-screen CNC machinists before a hands-on machine trial
Pre-screening CNC machinists before a hands-on machine trial protects your setters' floor time. Applicants arrive from staffing agencies, trade programmes, and shops that closed, and a resume lists Haas, Mazak, or Okuma without saying whether they set jobs up or only pressed cycle start. Ten minutes of recorded answers shows which controls they edit at, what tolerances they hold on which materials, how they measure, and whether they stop a setup that feels wrong.
What actually matters when screening CNC Machinist candidates
- 01
Hands-on competence
Check machines and controls they have run, materials cut, and the tolerances they hold routinely.
- 02
Safety discipline
Test guarding, workholding, and their response when a setup feels wrong but the schedule is tight.
- 03
Fault finding
Assess how they respond to chatter, tool wear, or a part drifting out of tolerance mid-run.
- 04
Reliability and conduct
Judge attendance across shifts, first-off inspection discipline, and how they hand over a running job.
Pre-screening questions to ask CNC Machinist candidates
12 questions grouped by what they test. Ask the same set in every screen and score answers on a consistent scale, or send them as an async video screen and compare answers side by side.
Machines and materials
Which CNC machines and controls have you run? Name the makes and the control type.
Specific pairings such as Haas VF-3 with Haas control, Mazak with Mazatrol, or DMG Mori with Fanuc, plus mill or lathe distinction.
Generic answers like "mills and lathes" with no make, model, or control they can name.
What materials have you cut, and which gave you the most trouble?
Named materials such as 6061 and 7075 aluminium, 4140, 316 stainless, Inconel, or titanium, with feeds, coolant, or tool wear differences noted.
Says "metal and plastic" and cannot explain why stainless or Inconel behaves differently from aluminium.
Can you read and edit G-code at the control, and what do you typically change?
Concrete edits: tweaking feeds and speeds, adjusting wear offsets, adding a tool change, fixing a wrong work offset, or restarting mid-program safely.
Claims to read G-code but cannot name a single code or describe one edit they made at the machine.
Do you have experience with 5-axis machining, and if so on what parts?
Honest scope: trunnion or head-head machines, 3+2 positioning versus simultaneous, fixture design, and collision checking before proving out.
Overclaims 5-axis experience but describes work that is clearly indexed 3-axis with a rotary table.
Setup and safety
Walk me through how you set up a job from a fresh print: first cut to first-off inspection.
An ordered routine: reviewing the print and datums, workholding, tramming, tool offsets, single-block prove-out, then measuring the first-off before running.
Skips prove-out or first-off inspection and goes straight from loading the program to production quantities.
Tell me about a time a setup felt wrong but the schedule was tight. What did you do?
A real stop-the-job decision: unsafe workholding, missing guard, worn tooling, or a suspect program, escalated to a supervisor with the reasoning explained.
Says they ran it anyway to hit the ship date, or cannot recall ever raising a safety concern.
Fault finding and quality
A part starts drifting out of tolerance halfway through a run. Talk me through what you check first.
A logical sequence: tool wear and insert condition, offsets, thermal growth, chip build-up in the fixture, coolant, then program or workholding movement.
Immediately blames the program or the machine and calls maintenance without checking tooling or offsets.
How do you handle quality control on a production run: what do you check, and how often?
Named practice: first-off inspection signed off, in-process checks at set intervals or SPC sampling, recording results, and quarantining suspect parts.
Relies on eyeballing parts or says the inspection department catches anything wrong.
Which precision measuring tools do you use daily, and what is the tightest tolerance you hold routinely?
Micrometers, bore gauges, height gauges, thread and pin gauges, CMM familiarity, with a numeric tolerance such as plus or minus 0.0005 inch on a bore.
Only mentions calipers, or quotes a tolerance without naming the feature or the gauge used to verify it.
Describe the most complex part you have machined, and show us the part, print, or a photo if you can.
A specific part with material, operations, tolerance, fixturing challenge, and what they changed to make it repeatable; visual evidence is a strong signal.
Vague description with no dimensions, no tolerance, and no explanation of what made it difficult.
Experience and availability
How many years have you been machining, and which shifts can you work?
A clear timeline with employers or apprenticeship, plus straight answers on nights, weekends, overtime, and how far they travel to site.
Vague total years, unexplained gaps, or shift availability that contradicts what the role clearly requires.
Do you hold any machining certifications, such as NIMS credentials or a completed apprenticeship?
Named credentials with the awarding body and year, or an honest statement that their training was on the floor with who mentored them.
Claims certifications they cannot name or date, or is evasive about where their training came from.
How to score responses
Score every candidate on the same four criteria immediately after the screen. At this stage you are shortlisting for panel interviews, not making the final call.
| Criterion | What a 5 looks like | Scale |
|---|---|---|
| Hands-on competence | Runs your machine and control types independently, holding tight tolerances across the materials you cut. | 1 · 2 · 3 · 4 · 5 |
| Safety discipline | Rigorous on workholding and guarding, and can describe stopping a run over a setup that felt wrong. | 1 · 2 · 3 · 4 · 5 |
| Fault finding | Diagnoses chatter, wear, and drift by cause rather than by guesswork, and adjusts before scrap accumulates. | 1 · 2 · 3 · 4 · 5 |
| Reliability and conduct | Reliable across shifts, disciplined on first-off inspection, and hands over jobs cleanly. | 1 · 2 · 3 · 4 · 5 |
Async video lets you hear a machinist describe chatter, tool wear, and a tolerance call in their own words, and see them hold up a finished part, a micrometer, or a first-off inspection sheet on camera.
Try it on HirevireScreening FAQ
Process basics
How long should a CNC machinist screening take?
Keep it to ten minutes of recorded responses. Four short text answers on machines, controls, materials, and certifications, plus three or four audio or video answers on setup, safety, and a part they made, gives you enough to decide on a trial. Anything longer loses machinists who are answering on a break between shifts.
Should I ask about certifications like NIMS?
Ask, but treat it as supporting evidence rather than a gate. NIMS credentials, an apprenticeship completion, or a City and Guilds qualification confirm formal training, yet many capable machinists learned entirely on the floor. Weigh the certification alongside what tolerances they hold and whether they can describe their own first-off inspection routine.
Evaluating answers
What tells me a machinist actually set up jobs rather than just ran them?
Setters talk about workholding, offsets, and proving out. Listen for tramming a vice, touching off tools, setting work and tool offsets, single-block proving at reduced rapid, and adjusting wear offsets after a first-off. Operators tend to describe loading parts, pressing cycle start, and calling a setter when something goes wrong.
How do I judge a machinist's safety answer without sounding like a compliance quiz?
Judge the specific decision, not the vocabulary. A strong answer names guarding, door interlocks, lockout tagout during tool changes, and chip handling, then describes one time they stopped a job: an unsafe workholding setup, a worn collet, or a suspect program. Someone who only recites policy titles has probably never made the call.
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Sanat has personally screened 300+ candidates across 18+ years of building and hiring teams, and turned that screening process into Hirevire's video screening platform. LinkedIn
