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 is a recognized cause of CNC workpiece ejection during milling? → Insufficient clamping force for the cutting forces generated
2. What is the main advantage of using coated carbide inserts over uncoated ones? → Increased hardness and wear resistance at elevated temperatures
3. What is 'chip load' (feed per tooth) in CNC milling? → The amount of material each cutting edge removes per revolution
4. What unit is spindle speed (RPM) typically calculated from when setting up a CNC cut? → Cutting speed (SFM or m/min) and tool diameter
5. What does the G96 code activate on a CNC lathe? → Constant surface speed (CSS) mode
6. In a CNC program, where is a block skip command typically placed? → At the beginning of a block with a forward slash /
7. What is the function of cutter radius compensation (G41/G42) in CNC programming? → It offsets the tool path to account for the physical radius of the cutter
8. A CNC operator notices the surface finish deteriorating progressively worse as a production run continues. What is the most likely cause? → Tool wear is increasing cutting forces and reducing edge sharpness
9. In CNC programming, what does a negative Z value typically indicate when using a standard right-hand coordinate system? → Movement downward, into the workpiece
10. What is the safest method for removing a broken end mill from a CNC spindle taper? → Use the machine's drawbar release function with the spindle fully stopped
11. What is the purpose of a coolant in CNC cutting operations? → To reduce heat, lubricate the cut, and flush away chips
12. What is the function of the F-word in a CNC program block? → Feed rate
13. What does the T-word followed by a number specify in a CNC program? → Tool change number
14. What is the primary purpose of the rake angle on a cutting tool? → To control chip flow and cutting forces
15. What instrument is used to measure the inside diameter of a precision bore in CNC quality inspection? → Telescoping gauge with outside micrometer
16. What is the function of a through-spindle coolant (TSC) system on a CNC machining center? → To deliver coolant directly through the tool to the cutting edge
17. Which of these won't contribute to ensuring machine safety? → Multi-tasking
18. In CNC turning, feed rate is most commonly expressed as: → Inches per revolution (IPR)
19. In precision measurement, what does 'gauge R&R' study evaluate? → The repeatability and reproducibility of a measurement system
20. What is the 3-2-1 locating principle used for in CNC workholding? → Constraining all six degrees of freedom with the minimum number of contact points
21. When roughing hardened steel (>45 HRC) on a CNC machining center, the recommended approach is: → Lower cutting speeds, smaller depths of cut, and robust carbide tooling
22. What is 'depth of cut' (DOC) in CNC milling? → How deep the tool engages the workpiece in the axial direction
23. In the event that a machine has CNC control, → Control is achieved by employment of alphanumeric data
24. What does the CNC term 'dry run' mean? → Executing the program at reduced feed with no workpiece installed to verify motion
25. In GD&T, what does the symbol for 'perpendicularity' look like? → An upside-down T (⊥)
26. What causes 'stick-slip' in older CNC machine slideways, and how is it typically corrected? → Insufficient lubrication causing jerky motion at low feeds; corrected with proper way oil
27. What does the M03 command do in a CNC cutting program? → Starts the spindle clockwise
28. The tapping cycle on a machine center is displayed using the G code, which is → G89
29. Which character is used to indicate a program end and rewind in a CNC program? → M30
30. Why should parallels used in a vise be matched pairs of the same height? → To keep the workpiece level and prevent rocking during machining