A NIMS CNC milling credential does not test obscure codes. It tests whether you can read a standard mill program, which means a focused, predictable set of G-code. Here is the realistic scope to study. Always confirm the exact requirements against the current NIMS standards, since credentials are revised over time, and treat this as a study list, not the actual exam.
The standard mill set
| Code | Meaning | Why a mill test expects it |
|---|---|---|
G00 / G01 | Rapid / linear feed | Every positioning and cutting move |
G02 / G03 | Clockwise / counterclockwise arc | Contours and radii |
G17 | XY plane select | The default milling plane |
G20 / G21 | Inch / millimeter units | Units awareness |
G90 / G91 | Absolute / incremental | Positioning mode |
G54-G59 | Work coordinate offsets | Where part zero is set |
G43 | Tool length compensation | Z handling per tool |
G40-G42 | Cutter compensation off/left/right | Contour accuracy |
G28 | Reference (home) return | Safe machine moves |
G81 | Drilling canned cycle | An everyday milling operation |
How deep to go
For the motion and setup codes, you should recall them instantly and explain what they do in a program. For canned cycles like G81, know what the cycle does and the role of its parameters, even if you would look up exact syntax on the job. The credential is checking practical reading fluency, not memorization of every parameter.
Drill the set for recall
This is a finite, knowable list, which makes it perfect for recall practice. Drill the common G-codes first, get the modal behavior right (offsets and positioning modes are modal), and use the method in beginner CNC code practice. For the broader credential, see the NIMS CNC operator test guide. A free tool like G-Code Sprint drills the mill set for fast recall.
Bottom line
The G-code on a NIMS mill test is the standard milling set: motion, plane, units, positioning, offsets, compensation, reference return, and basic canned cycles. Learn that finite list cold and confirm the scope against current NIMS standards.
Sources
- NIMS (National Institute for Metalworking Skills)
- LinuxCNC G-code reference (mill codes, canned cycles)
- CNCCookbook: G-code and M-code cheat sheet
Frequently asked questions
What G-codes should I know for a CNC mill certification?
The standard mill set: G00 to G03 for motion, G17 for the XY plane, G20/G21 for units, G90/G91 for positioning, G54 to G59 for work offsets, G43 for tool length and G40 to G42 for cutter compensation, G28 for reference return, and common canned cycles like G81 drilling.
Does a NIMS mill test include canned cycles?
Milling credentials commonly expect awareness of basic canned cycles such as drilling (G81) and related cycles, since they are everyday milling operations. Confirm the exact scope against the current NIMS standards for your credential.
What is the best way to learn the mill G-codes for a test?
Drill them for recall, not recognition. A free tool like G-Code Sprint quizzes the common mill G-codes both directions and repeats the ones you miss, so reading a mill program becomes automatic.
G-Code Sprint is a study and practice tool only. It is not affiliated with NIMS and does not provide official exam content. Always follow your instructor, employer, machine manual, and shop safety procedures.