CNC Cheat Sheet 2026

The 30 highest-yield CNC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. Which of the following best describes 'axial depth of cut' (ADOC) in CNC milling? → The depth the tool engages the workpiece along the spindle axis
2. Which measurement tool can provide readings in both metric and imperial units? → Digital caliper
3. What is the primary function of a tool length offset (TLO) in CNC milling? → To account for differences in tool length so Z-axis positions remain accurate
4. What is the primary ethical obligation of a CNC professional when a conflict of interest arises during g-code & m-code programming activities? → Disclose the conflict to all relevant parties and recuse from the decision if necessary
5. What is the purpose of specifying a 'dwell' (G04) command in a CNC boring cycle? → To pause spindle rotation at the bottom of the bore for a timed period to improve finish
6. What does the surface finish symbol 'Ra' represent in machining drawings? → Arithmetic average roughness of a surface profile
7. Why is it important to clean the machine after use? → To maintain performance and tool life
8. What is the purpose of zero return in CNC machines? → Set reference positions
9. Which of the following surface finish values represents the smoothest machined surface? → 16 Ra (micro-inches)
10. What is G-code used for in CNC programming? → To control machine operations
11. Which of the following is a fundamental principle of work holding & fixturing as it applies to Computer Numerical Control Machinist Technical? → Systematic evaluation and adherence to established industry standards
12. Why is simulation important before actual machining? → To test program and avoid errors
13. A CNC professional encounters an unfamiliar situation while performing gd&t symbol interpretation duties. What is the most appropriate first action? → Consult relevant standards, guidelines, or a qualified supervisor before proceeding
14. What is the purpose of section views in blueprints? → To reveal internal structures
15. What does a go/no-go gauge determine? → Dimensional conformity
16. What does the symbol Ø represent in a technical drawing? → Diameter
17. A 'datum' in CNC setup is best defined as: → A reference surface, point, or axis from which all measurements are made
18. Which instrument measures internal dimensions precisely? → Inside micrometer
19. What does the M-code typically control in a CNC program? → Spindle and auxiliary functions
20. What is the main goal of machine maintenance logs? → Track service history and issues
21. When machining stainless steel (304 SS), which approach is preferred to reduce work hardening? → Continuous cuts with adequate chip load to stay below the work-hardened layer
22. What is the main functional reason for specifying a specific surface finish on a sealing face (e.g., O-ring groove)? → To ensure the surface is smooth enough to prevent fluid leakage past the seal
23. In CNC turning, which insert nose radius produces the best surface finish at a given feed rate? → Larger nose radius
24. Which of the following is a fundamental principle of ferrous & non-ferrous material properties as it applies to Computer Numerical Control Machinist Technical? → Systematic evaluation and adherence to established industry standards
25. Which quality assurance method is most commonly applied in work holding & fixturing to verify that CNC professional standards are being met? → Structured audits, peer reviews, and performance metrics aligned with industry benchmarks
26. What is the primary ethical obligation of a CNC professional when a conflict of interest arises during cnc lathe turning operations activities? → Disclose the conflict to all relevant parties and recuse from the decision if necessary
27. Which quality assurance method is most commonly applied in cnc mill setup & operation to verify that CNC professional standards are being met? → Structured audits, peer reviews, and performance metrics aligned with industry benchmarks
28. Which symptom most strongly indicates that spindle speed is too high when turning hardened steel? → Blue or discolored chips curling away from the cut
29. What is the primary ethical obligation of a CNC professional when a conflict of interest arises during cnc mill setup & operation activities? → Disclose the conflict to all relevant parties and recuse from the decision if necessary
30. On a CNC lathe (turning center), the Z-axis zero point is most commonly set at: → The face of the finished workpiece