I have always told managers that the one decision that is the most important one they will ever make is hiring.
No other decision has the potential to cause so much pain if done poorly, or to make the manager’s job and the underlying business more successful if done well. Yet many hiring managers go into the process without having thought about it much, treating is as a distraction that they fiddle with, and often waiting for some sort of consensus among the interviewers to make the final decision easy.
Like anything else, there’s no free lunch, but what makes the job easier and the outcome more successful is to do a little homework. For example, think about the questions you want to ask your job candidates way ahead of time. What are you trying to find out and how will that affect the outcome of the hiring process? Keep a list of questions and review it every single time you use it to see how you can improve it.
Before too long, your list of interview questions will be a valuable tool that’s always ready to go the next time you need to hire.
Job Applicants, same story. Don’t just go from interview to interview responding to what happens–get ahead of the curve and do your homework. Seek out lists of good interview questions and think about what your best answers should be. Make your own list of questions that you know didn’t go so well on some interview or another and work on your answers until you’re happy to get the same question again.
For both groups, here are 50 CNC job interview question ideas to get you started. They’re divided into the following broad categories:
– Machining: The basic nuts and bolts of making chips on a machine.
– Metrology: Measurement and precision is very important to machinists. Is your candidate up to snuff?
– Personality and Problem Solving: Skills are just table stakes. The really awesome guys in the long run are great problem solvers that get along well with everyone and have the right work ethic. This is the hardest category to judge since everyone has their “interview face” on, so I have the most questions here.
– Programming: Everything from reading prints to using CADCAM to reading g-code is in this category.
One more thing: don’t think for a minute the only thing you can get out of all the work of being an interviewer or an interviewee is to match a job to the right hire. Interviews are always a chance to learn. I’ve learned many things in interviews, both as the job applicant and as the hiring manager. Go to school on the other guy’s experience and you can benefit from every hiring cycle just in knowledge gained and contacts made.
Here are the questions, and I’ve tried to provide links to resources to help you study up on what the good answers are:
1 Describe how you go about calculating feeds and speeds and how you determine cut depths and cut widths for a particular operation. Machining
Everyone has their own ideas on this one (what, everyone doesn’t use G-Wizard Calculator?), so your goal is to see how compatible the applicant’s approach is with what your shop needs. We’ve got an article on how to optimize Cut Depth and Cut Width for 2 1/2D machining. When you’re 3D profiling the rules change (does your applicant know the strategies for both?). CAM developer Robert Grzesek wrote a fabulous guest post for us on how to choose your stepover for 3D work.
Don’t be afraid to drill down and ask about subjects like High Speed Machining or Chip Thinning if it looks like a productivity way to explore your applicant’s deeper skills set.
2 Do you know manual machining? Walk me through an example of a part or operation you recently had to do on a manual machine. Machining
This is one of those deals where they have to convince you they know a topic cold, at least if you need them to know it. Don’t be afraid to grab a piece of bar stock and a micrometer and head out to the shop to have the applicant turn the stock to a particular OD on the lathe. You’ll learn a lot watching how quickly they get it done and seeing how they go about it. Of course if you ask any group of machinists whether CNC’ers need to know manual machining, you’ll get a ton of controversy!
3 How would you machine a square block from round stock? Machining
Another one aimed at a basic skill.
4 Describe the types of routine maintenance you’ve regularly performed on CNC machines. Machining
Every shop has routine maintenance that has to get done. Lubrication, coolant maintenance, and other tasks. You need to know if this applicant will help get that work done. Don’t be afraid to drill down deeper and ask them about more sophisticated maintenance they may have been involved with. You can even ask whether they were involved the last time a tech was brought in to fix a machine and get the story to help understand how well they followed what the tech did.
5 Share an experience where you identified a problem with a machine Machining
If the machines stop, the work often stops until they’re running again. Can your applicant diagnose and fix a problem without having to wait for the techs every time?
Be sure to also investigate whether they ever discovered a problem that wasn’t obvious based on symptoms. The sounds of bearings starting to go or something similar. Having your people on the machines be able to notice when there’s something wrong before it goes way wrong can save you a lot of money.
6 Describe the most interesting fixture you’ve made and what made it great. Machining
Fixtures are a huge productivity opportunity. You’ll want to understand whether the applicant has skills in this area and understands the productivity issues.
7 Walk me through a problem you recently solved using trigonometry or other shop math. Machining
A decent grasp of Shop Math is pretty important for many CNC positions, and something you’ll likely find hard to teach if they don’t already need it.
Need a little help with your shop math?
G-Wizard has a comprehensive set of geometry calculators built right in you can play with and use to check your work.
8 Tell us what fixture or tooling you’ve encountered in your career that saved your shop the most money Machining
Even if they don’t make fixtures, they still need to understand and use them. But, it’s also important to understand their economics.
Depending on their role, you will also want to understand whether they know when not to build a fixture and how to optimize the return on fixture investment.
We offer a Free Fixture Calculator that helps play some what-if games so you can get your head around fixture decisions.
9 Can you use a calipers, dial indicator, and read a micrometer? Metrology
Measurement is a constant issue around the shop. Get into it early.
Here are some deeper question to explore to test the depth of knowledge:
- Do they know about cosine error on dial indicators?
- Can they use a snap gage to reliably determine a bore’s inner diameter? Hand them a mic, snap gage and bore to see. It can take a little touch to get it right.
10 Hand them some artifacts, a calipers, and a micrometer and ask them to measure various features on the artifacts Metrology
Give them some of the parts your shop is making and inspecting and ask them to measure features you’ve already measured. Don’t be afraid to go out to a machine with a DTI and have them sweep some things too, that’s another important skill.
11 Share an experience in which you measured finished workpieces to ensure conformance to specifications Metrology
This is your chance to hear about their inspection experience elsewhere. If it seems worthwhile, drill down into more detail and see what you can learn.
12 Have you ever worked with a CMM? Tell us about your experiences with one. Metrology
This is not a skill everyone will have, but CMM’s (Coordinate Measuring Machines) are turning up on shop floors more and more. It’s worth knowing whether your applicant can handle one even if that isn’t in the cards for the initial job.
13 Can you communicate? Personality & Problem Solving
The question is short and somewhat nebulous for a reason–a good communicator can overcome the communication shortcomings of whomever they’re talking to.
14 Who were the 3 best colleagues you ever worked with and why? Personality & Problem Solving
This is your chance to go to school in so many ways. You’ll learn how your applicant judges others, which is always useful. You should take down the names of and where these 3 folks are working as part of the process. Now you’re building a database of people who at least your applicant thinks are great catches. Sort of like doing the references before you even know the guys and before anyone realizes that’s what you’re doing. I’ve gotten a lot of good hires this way. I often assign this question to someone on the interview team who is clearly not a manager as it changes the dynamics and makes the answers even more interesting.
Another variation on this question (I’d have two different people each ask the two versions): Which colleagues have taught you the most? What’d you learn from them and what, if anything, made them effective teachers?
15 Describe an experience on the job that made you very happy Personality & Problem Solving
What does your applicant like? How do you make him love your workplace? Will he love your workplace?
Be sure to ask the reverse: Describe an experience on the job that made you unhappy.
16 Describe an experience where you analyzed data in order to suggest new approaches that made a difference Personality & Problem Solving
Can the applicant analyze data in order to formulate a solution?
17 Describe an experience where you anticipated a problem with a new process and helped prevent the problem from occurring in advance Personality & Problem Solving
Process is a huge part of manufacturing. How comfortable is your applicant in thinking about it? So comfortable they can visualize problems with a process that hasn’t even gone into production yet? A guy like that might be pretty handy to have around.
18 Describe an experience where you had to offer an unpopular opinion and convince others to follow it in order to succeed Personality & Problem Solving
Is your applicant strictly a “Yes” man, or can he speak up if he sees the train is about to come off the track? Can he speak up with an unpopular opinion in a way that helps others to get on board, or is he just a complainer?
19 Describe an experience where you went to a colleague or peer to get help that made a substantial improvement in your work Personality & Problem Solving
If I had a nickel for every time an employee could have gotten around some problem or challenge sooner just by asking for help sooner, I’d have a lot of nickels!
The best employees know when to get help. In fact, they crave every opportunity to learn and get better at their craft.
20 Describe an experience where you were able to help your employer achieve significant cost savings Personality & Problem Solving
Does your applicant even care about helping achieve cost savings? Are they good at it?
21 Describe how you organize, plan, and prioritize your work Personality & Problem Solving
Process extends to how an individual manages their own work too. By the way, if you want to learn to radically improve your productivity, I offer a free 5 lesson video course that teaches all the Productivity Hacks I use constantly.
22 Describe the best manager you ever worked for. What made them special? Personality & Problem Solving
This is another one where you get to learn about a potential resource for a future hiring cycle (that stellar manager your applicant loves) as well as how your applicant evaluates their management.
23 Describe the worst manager you ever worked for. What made them so difficult? Personality & Problem Solving
Ditto to #22.
24 Describe things you’ve done to reduce stress on the job Personality & Problem Solving
All jobs carry some stress, some more than others. A key skill is being able to deal successfully with stress, perhaps even helping others reduce their stress. Also, if your applicant can’t make a convincing argument they have ever felt stress, you have to wonder whether they care much about helping the team to succeed if the going gets tough.
25 Describe your most successful experience helping, teaching, or mentoring another individual in your shop Personality & Problem Solving
Do you have a real team player? Will they help everyone around them to be better at the job? Prove it!
26 Share an experience in which you successfully improved the quality of a product or process Personality & Problem Solving
Quality is another big deal for Manufacturing. Drill down on this area with your applicant. If your shop is into Lean Manufacturing, listen carefully to learn whether the applicant grasps the key principles you’ve adopted. Draw them out with deeper questioning.
27 Share an experience where inspection enabled you to identify a problem and the cause of that problem Personality & Problem Solving
OK, so you measured some parts and scrapped the ones that weren’t within tolerance. That’s table stakes. Can you actually prevent or reduce scrappage? Now you’re talking!
28 Share an experience where you proposed an improvement to a process to management and got them to adopt it Personality & Problem Solving
Can you bring great suggestions to the table and help me to understand why they’re great so that we can get them going? Many have good ideas but never share them. Many throw them out on a take it or leave it basis. It’s just never that easy. Who’ll go the extra mile to sell their idea until it can make a difference?
29 Tell us about the last time you had to negotiate with someone in a work setting Personality & Problem Solving
Negotiation is a part of working life. May as well see how someone handles it.
30 Tell us about the most stressful job you ever worked on Personality & Problem Solving
What does your guy really get bothered by? Also, this is your chance to hear about it from the employee’s perspective. Are you doing some of these things without even realizing you’re stressing people out in the process?
31 Tell us about the worst mistake you ever made on a job Personality & Problem Solving
We all make mistakes. There are really only two interesting things to discuss–how to avoid making the same mistake again and how to recover once a mistake is made.
32 Tell us about your proudest achievement in your work career Personality & Problem Solving
Always good to know what an applicant thinks they’ve done well. You’ll have to decide whether you’d value that kind of contribution or even make it possible.
33 What are the top 3 key abilities and skills for this position? Personality & Problem Solving
Do they understand the job the same way you do? Having heard their opinion, do they have some good ideas you want to adopt? After comparing their thoughts on the key skills for the position, share yours and see how the applicant reacts.
34 What are three positive character traits you wish you had but don’t? Personality & Problem Solving
Most people are not very self-aware. Those that do understand their weaknesses and want to get better are usually people with great attitudes. Beware the bogus interview face answers, “I always work too darned hard and get tired.” Throw those out until you get something real.
35 What do you see as your career path going forward from this position? Personality & Problem Solving
Can you provide this path, or are you setting this person up to start looking for another job not long after you’ve hired them?
36 What one personal trait has helped you the most in your career? Personality & Problem Solving
Do you value what they have to offer? It’s tough on an employee when you can’t use what they see as their best abilities.
37 What’s been your most effective source of learning for your machining career? Personality & Problem Solving
The best employees never stop learning. Does this person quote any learning opportunities that happened recently? Do they have some good ideas for you or your employees to learn going forward?
Be sure to ask what things they’re most interested in learning next. Are those things valuable to you? Can you help them learn them? That can be a great inducement to getting them to join your team.
38 Which personal trait has been the most challenging for you in your career? Personality & Problem Solving
Eventually people get told what their worst warts are. May as well have them tell you too if they’re willing. It’s back to that self-awareness thing.
39 Would you rather write a report or deliver it verbally? Personality & Problem Solving
Communication of both kinds is valuable. Most of the time you’d love to have both. Another one to ask about is whether they prefer phone, instant messages, or email? If you’re going to manage this person, or they have to be part of a team that needs to communicate, it helps to align communication styles.
40 What was the worst shop accident you’ve seen and how could it have been avoided? Personality & Problem Solving
Shop Safety is critically important. Find out how aware your applicants are, how skilled they are, and whether they have got “religion” about shop safety.
41 Describe the most difficult setup task you’ve ever encountered Personality & Problem Solving
Exacting setups really test a machinist’s skills. OTOH, they may tell you something that sounds easy to you and that’s a red flag worth learning sooner than later.
42 Describe the most difficult skill to learn that you have mastered Personality & Problem Solving
Will they work hard to obtain new skills? Can they learn even the most difficult skills? Good to know those things.
43 Can they CAM program? If so, which programs and versions Programming
Not everyone can CAM, but those that can are valuable.
44 Can you hand program g-code? (Very important for finding CAM problems) Programming
Even if they don’t CAM, can they deal with problems down on the Shop Floor without sending the g-code back through the CAM cycle again?
Even if they can’t hand program, do they at least know the 9 simple g-codes needed to be handy with MDI?
If your shop machines have the capability, it’s worth knowing if they can use the Conversational CNC on your controls.
45 Can you read prints? Programming
This is another terse one that invites them to give a free-form response. Don’t settle for a simple yes or no, make them dig into it. Be sure to focus on issues like:
- What are some recent cases where a print was unclear? How did they go about clarifying it?
- Give an example where misunderstanding a print caused a lot of extra work and potentially scrapped parts?
46 Explain the difference between Cartesian and Polar coordinate systems and examples of what each is good for. Programming
Half shop math and half programming. Polar coordinates are super handy for a lot of problems. Here’s a free calculator to help with Polar and Cartesian coordinates.
47 Do you understand Geometric dimensioning and tolerancing? Programming
Do they know GD&T? It’s becoming increasingly essential to understand Geometric Dimensioning and Tolerancing in the CNC World (We have a free course on it, BTW!).
This is a fairly complex subject that’s crucial for a lot of jobs. Be sure to drill down and not just take a simple yes or no answer–make them prove it.
48 Give them a blueprint and ask them to describe how to make the part. Programming
This one is the essence of being able to synthesize so many critical skills for machinists.
Follow up: Ask how they’d quote that part. If you think you’d ever use them to quote parts, this is a good time to explore their experience in the area.
49 Have they taken any courses in Statistical Process Control? Programming
SPC is another valuable tool we see more and more often in Manufacturing.
50 Share an experience where you modified a g-code program based on problems encountered during operation Programming
Ask for lots of details. Consider taking a simple g-code program, introducing some errors, and asking them to help fix the errors. You might even walk them through “air cutting” a bad program, being careful to make sure they don’t screw up.
Many more questions are possible. There’s probably 5 or 6 just around topics like Tool Offsets and how they’re used that go to the heart of day to day machine work.
Don’t be afraid to ask lots of questions. Get help from an interview team so the questions are spread around. And don’t be afraid to assign out some key questions you want to have answered to the interview team, or at least to have each team member focus on some specific area. If a member of your team is an expert on some area, they’ll be a better judge of the applicant’s abilities in that area, so assign the topics accordingly.
And remember, your hiring decision will have more bearing on whether you are enjoying or hating your job than almost anything else you can do!
Tell us your favorite interview question ideas below in the comments.
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Bob is responsible for the development and implementation of the popular G-Wizard CNC Software. Bob is also the founder of CNCCookbook, the largest CNC-related blog on the Internet.
Another fantastic column! I was searching for something like this not too long ago, to hire my first machinist, and pulling a few things off the net to try to help me make a good decision. I showed the guys a part that took a few setups and asked them to walk me through how they would do it. And I took the guys out to the shop and and asked them to show me to how to get the Bridgeport spindle square to the table, some basic g codes, and a few other things like that. But I wish I had what you wrote before, because you just added a lot of great ideas to the mix. Hats off to you sir!
Roy, thank you for the kind words.
we need the reference where the questions were taken from?
This is the number one question I ask a potential employee. Did you ever have a job before you were 16 years old? This simple yes or no answer tells you if that future employee has drive and wants to get ahead in life. Verses on the take like most of the potential employees I have interviewed. The job could be baby sitting for his or her younger siblings. It could be working for spending money. A paper route (which are almost extinct). Mowing grass. Anything that earns them some money for their services. We are all in sales. We sell our work to our boss, mom, dad, spouse, customer ect….