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What kinds of preventative maintenance have you performed on CNC machines in the past? 

Asking this question tests how important the CNC operator candidate considers machine maintenance to be. It also will indicate how much experience they have with maintenance and machine troubleshooting. If they have work experience, they should be able to relate specific examples when answering the question. Pay attention to the candidate's knowledge of potential problems that can happen when maintenance is neglected. What to look for in an answer:

Knowledge of CNC machines

Understanding of preventative maintenance

Ability to communicate technical information


"At Superior Metal Products, I was performing routine maintenance on three different CNC machines. We were provided guidelines by the process engineer and the user manual to follow."

Describe how you inspect finished parts to ensure that they meet all specs.

CNC machining involves creating precision parts in various ways, and CNC operators are usually responsible for checking that the parts they produce meet specific dimension measurements. Operators should understand tolerances and be familiar with quality control practices. Pay attention to how much detail the candidate pays to balancing production against quality assurance and the importance of adhering to a manufacturing process. They should also be familiar with accurate measuring techniques and tools. What to look for in an answer:

Knowledge of blueprints

Understanding of measuring devices

Familiarity with quality assurance

Example: "I spot check parts if the process doesn't specify inspection standards using the tolerances listed on a part's blueprint. I especially watch for easily missed or critical measurements." 

Describe the most interesting part that you've made in the past.

CNC operators sometimes encounter complex part drawings that require a multi-step manufacturing process. Most experienced candidates will have an example they can share without much trouble. Asking this question helps you gauge how much experience the candidate has with complicated CNC programs. It can also give you an idea of how efficiently they can handle problems with programs that need code changes or measurement adjustments. What to look for in an answer:

Experience with complex CNC programs

Ability to handle problems with CNC programs

Familiarity with difficult manufacturing processes

Example: "The most challenging project I've worked on was a prototype control box housing. I needed to adjust several program steps with the help of a process engineer." 

What's an example of a time you argued for a process change, and how did you go about it?

Manufacturing processes often are improved thanks to insights from production workers like CNC operators. CNC programs sometimes aren't as efficient as they could be when new parts are introduced, which is something operators can bring to the attention of engineers. Experienced candidates should have examples of these situations that they can discuss. Sometimes operators need to be assertive with engineers, so pay attention to the candidate's approach to dealing with disagreements. What to look for in an answer:

Attention to potential CNC program improvements

Ability to make CNC programs more efficient

Assertiveness when communicating ideas to engineers


"I recall a slow program that wasn't run very often at my previous employer. Each time, I'd bring it to the engineer's attention in a professional manner until they fixed it."

How do you handle time pressure when a job needs to ship the same day?

Production workers often find themselves in situations that require stress management when orders need to ship as soon as possible. Asking this question will gauge a CNC operator candidate's experience with time pressure, but it'll also shed light on how much they consider customer satisfaction. Pay attention to the level of professionalism they apply to the problem as they answer. For example, they should indicate that how the situation came about is unimportant. What to look for in an answer:

Importance of customer satisfaction

Time management skills

Professional attitude


"I've been under the gun a few times because of back-ordered parts. I do the best I can and offer to stay late if it's needed."

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