How should I test an operator before hiring?

A CV that lists years on CNC lathes tells you which machines a person has stood beside. It says nothing about whether they wipe the anvils before closing a micrometer. Nor does it show what they do when a bore creeps oversize as the boring bar's tip wears. Those habits decide whether your spindles make good parts on second shift, and a short practical test brings them out in about an hour.

So here is the short answer. Hand the candidate one of your own drawings, your own gauges and a part that came off your machines last week. Ask them to read the print, pick tooling, measure the part and run a proven cycle with your setter beside them. Write down what a pass looks like before they arrive. Then score what you saw, not what you heard.

A loader, an operator, a setter and a programmer each need different proof. Quizzing a loader on G-code wastes the hour. Testing a setter only on gauging misses the part of the job you are paying for. Before anyone is called in, write the grade as the sheet's heading and mark which stations that grade must clear.

• Loader or helper: safe handling of bar and blanks, deburring to the drawing, reading a vernier, and knowing when to stop and call someone.
• Operator: reading tolerances and datums, measuring with a micrometer and bore gauge, spotting an out-of-limit part, and finding the wear offset page.
• Setter: touching off tools, setting a work offset, choosing insert grades, and proving and signing a first piece.
• Programmer: writing or checking a short program, choosing a toolpath strategy, and catching a dangerous rapid move before it reaches the spindle.

1. 1

   The drawing

   Give them a print of a part you make, with a thread callout, a surface finish symbol, a chamfer note and at least two toleranced diameters. Ask which sizes are critical, what the limits are on two of them, and which face the part is dimensioned from. Ten minutes is plenty.

2. 2

   Tools and inserts

   Lay out a few carbide inserts with different chipbreakers, a drill, a grooving tool and a boring bar. Ask which they would use to rough and finish a shoulder, and why. A good answer mentions nose radius, chip breaking or the material, even in plain words.

3. 3

   Measuring a sample part

   Offer a part with one diameter placed just outside the limit, plus a thread to try with a go and no-go plug. Let them choose instruments. Notice whether they wipe the faces, check zero against the setting standard, turn the ratchet rather than the thimble, and let a warm part cool. Finding the faulty size is the pass.

4. 4

   A proven cycle, with the setter alongside

   Load a program you trust on scrap bar or a cheap aluminium block. Ask them to step through it block by block with the feed override turned down, then point to the offset they would change if the diameter grew. The setter keeps a hand near feed hold.

5. 5

   One question about nights

   Put one question to them: an alarm stops the machine after midnight and no setter is on site, so what happens next? You want to hear that they would stop, note the alarm and phone, not reset and hope.

Most hiring arguments in a machine shop happen after the candidate has gone home. The setter liked one person, the owner liked another, and nobody had written down what they were looking for. A one-page score sheet settles this. Each assessor marks the stations alone and compares only at the end.

Candidate and grade tested: loader, operator, setter or programmer.
Drawing: named the critical sizes and read two tolerance bands correctly? Yes, partly or no.
Tooling: picked a sensible roughing and finishing insert and gave a reason? Yes, partly or no.
Gauging: cleaned and zeroed the instrument, then found the out-of-limit size? Yes, partly or no.
Machine: found the offset page, used single block, kept a hand near feed hold? Yes, partly or no.
Night question: would stop, record the alarm and call before resetting? Yes, partly or no.
Must-pass stations for this grade, written before the test.
Assessor one, assessor two, and the grade offered if any.

For an operator, gauging should be a must-pass. A person who cannot find a bad size will one day ship one. For a setter, the machine station joins it. A partly is not a failure; it shows what the first month of training has to cover.

For a test of an hour or so, many shops cover travel and offer tea. Once a trial stretches into a full shift and produces parts you will sell, it has become work. Treat it and pay it as work. Decide which kind you are running and tell the candidate beforehand.

Screens, soft keys and handwheel layouts differ between makes, and a capable operator learns new menus within days. Test the thinking, not the buttons. Tape a printed copy of your offset page beside the panel and let them use it. Someone who understands why a wear offset moves the diameter will find the right box. Someone who cannot read a micrometer will not learn it in a week.

Keep the five stations and add depth. A setter candidate should touch off at least one tool, set a work offset with an edge finder or probe, and talk you through proving a first piece. For a programmer, print a short program with three planted faults: a feed far too high, a missing coolant code and a rapid move that would plunge through the part. Ask them to circle the faults in pen. It takes fifteen minutes and separates people who read code from people who only post it out of CAM.

Your senior setter knows the work and should run the machine station. A second person, the owner or whoever handles hiring, keeps time and keeps the scoring honest. Use the same drawing and sample for everyone applying for one grade, and lock them in a drawer between interviews. The question-by-question interview scorecard sits well beside the trade test.

Run a quick phone screen first for shift preference, notice period and travel. Then the test, then a talk about the grade ladder and pay, then the offer. Sourcing is its own problem, covered in where to find machinists worth testing. Units adding spindles can also read recruitment notes for VMC machining units. The trade's broader people issues sit on our machine shop and precision engineering overview. If you want a test built with you, grade by grade, that is part of recruitment process consulting, and you can tell us which roles you are filling.