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CNC Programmer interview questions, and what a good answer sounds like

A CNC programmer interview usually ends with a print on the table and someone asking how you'd make the part. The questions before that are testing whether your programs will run on second shift without a phone call. Here's what gets asked and what the people across the table are listening for.

11 questions7 minute read

Part 1

1.Walk me through how you'd program this part, from the print to posted code.

Why they ask

This is the core of the job. They want to see an order of operations that makes sense and a habit of catching problems before the machine does.

How to answer

  • Start with the print: material, critical tolerances, datums, finish callouts and quantity
  • Decide setups and workholding before any toolpath, and say how you'll locate off the datums
  • Rough with an adaptive or high-efficiency path, then semi-finish and finish the critical features last
  • Simulate with stock and holders turned on, then post and check the code for tool changes and retracts
  • Write a setup sheet and plan to be at the machine for the first article

2.Which CAM software have you used, and what did you program with it?

Why they ask

They need to know how much training you'll need on their package and whether you've used it on work like theirs.

How to answer

  • Name the package and the version of the work: Mastercam mill, Esprit turning, NX multi-axis
  • Describe a real part and the toolpaths you used on it
  • Mention what you did beyond basic paths, like custom tool libraries, templates or post edits
  • If their package is new to you, say how the concepts map across and how you'd ramp up

3.Tell me about a crash or a scrapped part that came from one of your programs.

Why they ask

Every programmer has one. They want honesty, a clear root cause and proof you changed a habit afterward.

How to answer

  • Own it in the first sentence without blaming the operator
  • Name the specific cause, like a wrong stock model, a missed clearance plane or a holder that wasn't in the simulation
  • Say what you did that day to get the job back on track
  • Describe the permanent fix: a checklist step, a template change or turning on holder collision checks
4.How do you pick feeds and speeds for a material you haven't cut before?

Why they ask

Guessing burns tools and time. They want to hear a method grounded in real data and adjusted at the machine.

How to answer

  • Start from the tool maker's recommendations for that grade and coating
  • Adjust for rigidity, stickout, the machine's horsepower and the workholding
  • Use chip thinning math on light radial engagement instead of cutting slow everywhere
  • Prove it out conservatively, listen and look at the chips, then push it and update your tool library
5.How do you decide on workholding for a new job?

Why they ask

Programmers who ignore workholding write paths that can't be run. It also tells them whether you think about repeat orders and cycle time.

How to answer

  • Look at quantity, part shape and which features need to be in one setup to hold tolerance
  • Compare vises, soft jaws, dovetail fixtures, pallets and dedicated fixtures on cost and setup time
  • Think about tool reach and clearance before committing
  • Mention designing soft jaws or a simple fixture yourself when it saves setups

Part 2

6.An operator says your program chatters on a thin wall. What do you do?

Why they ask

This tests how you work with the floor and whether you know the actual fixes for chatter.

How to answer

  • Go look at it and ask the operator what they've already tried
  • Check stickout, holder choice and whether the wall is supported by uncut stock during finishing
  • Change the order so the wall is finished while it still has material behind it, or step down in lighter passes
  • Adjust speed to get out of the harmonic, and update the program so the fix sticks for the next run
7.How do you prove out a program before it runs in production?

Why they ask

They want to know how many of your jobs will need hand-holding at the machine.

How to answer

  • Full simulation with stock, holders and the machine model where available, in Vericut or the CAM's own verify
  • Read the posted code for the first moves, tool changes and work offsets
  • Dry run or single block the first part with the operator, with the feed and rapid overrides turned down
  • Measure the first article and adjust before handing it off
8.Have you ever edited a post processor?

Why they ask

Post problems cause strange, expensive errors. Knowing how posts work separates a CAM user from a programmer they can leave alone.

How to answer

  • Be straight about your level, from small tweaks to full rewrites
  • Give a real example, like adding a coolant code, a probing macro or a safe start block
  • Say how you tested the change before releasing it to every job
  • If you haven't edited one, explain how you'd work with the reseller to get it fixed
9.How would you cut cycle time on a job that's already running?

Why they ask

Shops make their margin on repeat work. A programmer who finds time on existing jobs pays for themselves.

How to answer

  • Watch the job run and time each tool, not just the whole cycle
  • Look for air cutting, slow roughing paths and extra tool changes
  • Swap in high-efficiency roughing, combine operations or cut a setup with better workholding
  • Check the change against quality and tool life, not just the clock
10.What does a good setup sheet include?

Why they ask

Setup sheets are how your intent reaches the floor. Weak ones cause most of the calls you'll get on night shift.

How to answer

  • Tool list with holders, stickout and tool numbers
  • Workholding, part orientation and where the work offset is picked up, with a picture
  • Stock size and any special notes like jaw pressure or deburr steps
  • Inspection points to check on the first part

Part 3

11.How do you handle a hot job dropped into your queue when you already have a full list?

Why they ask

Programmers sit between sales, scheduling and the floor. They want to see you handle priorities calmly.

How to answer

  • Ask who set the priority and what the real ship date is
  • Tell the scheduler which job slips if this one goes first
  • Use templates or a similar old program to get it moving faster
  • Keep the machines that are waiting on you in mind so the floor doesn't sit idle

Questions to ask them

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

  • Which CAM package and version do you run, and who maintains the post processors?
  • What's the mix of mill, lathe and multi-axis work, and which machines would I be programming for?
  • How are programs proven out here, and is the programmer expected at the machine for first articles?
  • How does programming work get prioritised, and who decides when a job jumps the queue?
  • What's the biggest recurring problem the floor has with the programs they get now?

Related interview guides

CNC Machinist