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. What is the main advantage of using coated carbide inserts over uncoated ones? → Increased hardness and wear resistance at elevated temperatures
2. What is 'chip load' (feed per tooth) in CNC milling? → The amount of material each cutting edge removes per revolution
3. What does the G96 code activate on a CNC lathe? → Constant surface speed (CSS) mode
4. In a CNC program, where is a block skip command typically placed? → At the beginning of a block with a forward slash /
5. 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
6. What is the function of the F-word in a CNC program block? → Feed rate
7. What does the T-word followed by a number specify in a CNC program? → Tool change number
8. What is the primary purpose of the rake angle on a cutting tool? → To control chip flow and cutting forces
9. What instrument is used to measure the inside diameter of a precision bore in CNC quality inspection? → Telescoping gauge with outside micrometer
10. Which of these won't contribute to ensuring machine safety? → Multi-tasking
11. In CNC turning, feed rate is most commonly expressed as: → Inches per revolution (IPR)
12. In precision measurement, what does 'gauge R&R' study evaluate? → The repeatability and reproducibility of a measurement system
13. 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
14. 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
15. In the event that a machine has CNC control, → Control is achieved by employment of alphanumeric data
16. In GD&T, what does the symbol for 'perpendicularity' look like? → An upside-down T (⊥)
17. What does the M03 command do in a CNC cutting program? → Starts the spindle clockwise
18. The tapping cycle on a machine center is displayed using the G code, which is → G89
19. Which character is used to indicate a program end and rewind in a CNC program? → M30
20. Why should parallels used in a vise be matched pairs of the same height? → To keep the workpiece level and prevent rocking during machining
21. The tool is moved with the GOO command at → Rapid traverse without machining
22. What is the chip load (feed per tooth) for a 4-flute end mill running at 3,000 RPM with a feed rate of 60 IPM? → 0.005 inches
23. What does 'dry run' mode do on a CNC machine? → Overrides all programmed feed rates with a single adjustable feed for program verification
24. Which G-code command is used for linear interpolation (straight-line cutting) at feed rate? → G01
25. What is the purpose of a center-cutting end mill designation? → The tool can plunge directly into material
26. In CNC lathe work, what is the primary purpose of a steady rest (fixed steady)? → To support long, slender workpieces and prevent deflection during machining
27. What is the correct formula for calculating spindle speed (RPM) from cutting speed (SFM) and tool diameter (D in inches)? → RPM = (SFM × 12) / (π × D)
28. What does Ra measure in surface finish inspection? → The arithmetic average roughness of the surface profile
29. What is the primary purpose of ball screw lubrication in a CNC machine? → To reduce friction, prevent wear, and maintain positioning accuracy of the linear axes
30. Which G-code activates incremental (relative) positioning mode? → G91