CNC Study Guide 2026
Everything you need to pass the CNC exam in one place: the exam format, every topic to study, real practice questions with explanations, flashcards, and full-length practice tests. Free, no sign-up needed.
📋 CNC Exam Format at a Glance
📚 CNC Topics to Study (21)
✍️ Sample CNC Questions & Answers
1. What is spindle speed measured in?
Spindle speed, which dictates how fast the cutting tool or workpiece rotates, is universally measured in Revolutions Per Minute (RPM). This measurement is a critical parameter in CNC machining, directly influencing the cutting speed, material removal rate, and surface finish. Proper RPM selection is essential for optimizing tool life and machining efficiency for different materials.
2. In CNC programming, what does the G28 command instruct the machine to do?
G28 commands the machine to return to its machine home (reference zero) position, typically passing through an intermediate point for safety.
3. When a drawing calls for a 'ground' surface, which post-processing step is implied?
A 'ground' callout means the surface is finished by grinding, achieving tolerances and finishes beyond what turning or milling alone can produce.
4. What does SPC stand for in quality control?
SPC stands for Statistical Process Control, which is a method used in quality control to monitor and control a process using statistical techniques. By collecting and analyzing data from a process, SPC helps identify variations, predict future performance, and ensure that the process remains within acceptable limits. This leads to consistent product quality and reduced defects.
5. What does an 'Rz' (Rzmax) measurement on a drawing indicate compared to Ra?
Rz averages the five largest peak-to-valley heights over the evaluation length, making it more sensitive to extreme surface events than Ra.
6. What is the function of a dial indicator?
A dial indicator is a precision measuring tool used to measure small linear displacements or variations in surface flatness, concentricity, or alignment. It converts linear movement of a plunger into rotational movement of a needle on a dial, providing a visual reading of deviations from a reference point. It's essential for checking runout, parallelism, and other geometric tolerances.