Module 1: CNC Fundamentals & Machine Architecture Assessment Quiz

Module: U4M1 - CNC Fundamentals & Machine Architecture Duration: 25 minutes Passing Score: 70% Format: Multiple choice and scenario-based

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What does CNC stand for in the context of machining?

Computer Numerical Control

Centralized Numeric Coding

Computer Network Controller

Calibrated Numerical Computation

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Explanation: CNC stands for Computer Numerical Control, referring to the automated control of machining tools via a computer that executes pre-programmed sequences of commands (G-code).

Which axis on a typical 3-axis CNC router represents the vertical (up/down) movement of the spindle?

Z-axis

X-axis

Y-axis

A-axis

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Explanation: On a standard 3-axis CNC router, the Z-axis controls the vertical movement of the spindle (plunge depth), while the X and Y axes control horizontal table movement.

What is the primary function of the spindle on a CNC router?

To hold and rotate the cutting tool at controlled RPM

To move the workpiece along the X-axis

To provide coolant to the cutting area

To clamp the material to the spoilboard

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Explanation: The spindle is the rotating assembly that holds the cutting tool (via a collet or tool holder) and spins it at the programmed RPM to perform cutting operations.

What component of a CNC router converts rotational motor movement into linear motion along the axes?

Ball screw or lead screw

Spindle motor

Stepper driver

Limit switch

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Explanation: Ball screws and lead screws convert the rotational output of stepper or servo motors into precise linear motion along each axis. Ball screws offer higher precision and lower friction than lead screws.

What is the typical spindle speed range for a mid-range CNC router used in a makerspace?

8,000–24,000 RPM

500–2,000 RPM

100–500 RPM

50,000–100,000 RPM

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Explanation: Mid-range CNC routers typically operate between 8,000 and 24,000 RPM. Higher-end industrial machines may reach 30,000+ RPM, while speeds below 5,000 RPM are more common on metal milling machines.

What is the purpose of a spoilboard on a CNC router?

To provide a sacrificial surface that protects the machine bed during through-cuts

To increase the rigidity of the workpiece

To provide automatic workholding via magnetism

To calibrate the Z-axis zero point

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Explanation: The spoilboard (typically MDF) sits on top of the machine bed and acts as a sacrificial surface. When cutting completely through material, the bit cuts slightly into the spoilboard rather than the machine table.

Which type of motor provides feedback on position and is commonly used in higher-end CNC routers?

Servo motor

Stepper motor

Universal motor

Induction motor

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Explanation: Servo motors use encoders to provide closed-loop position feedback, allowing the controller to verify actual position matches commanded position. Stepper motors are open-loop and can lose steps under heavy load.

What does "steps per revolution" refer to in the context of a CNC stepper motor?

The number of discrete angular positions the motor can achieve in one full rotation

The number of cutting passes required to complete one operation

The feed rate measured in inches per revolution

The number of G-code commands per toolpath cycle

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Explanation: Steps per revolution defines the motor's angular resolution. A typical stepper motor has 200 steps/revolution (1.8° per step). Microstepping can subdivide these for finer resolution.

In CNC terminology, what is "backlash"?

The play or lost motion between mechanical components when direction is reversed

The kickback force when the bit encounters a knot in wood

The vibration caused by excessive spindle speed

The error in Z-axis calibration

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Explanation: Backlash is the small amount of movement lost when an axis reverses direction, caused by clearance between mechanical components (gears, lead screws, nuts). It results in positioning inaccuracy and must be compensated for in the controller.

What is the function of limit switches on a CNC router?

To define the physical boundaries of travel and establish a home position

To control the spindle speed

To regulate coolant flow

To measure the length of the cutting tool

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Explanation: Limit switches (or proximity sensors) are placed at the ends of each axis travel. They prevent the machine from crashing past its physical limits and provide a reference point for homing/zeroing the machine.

A student notices their CNC router is producing slightly oversized circles. Which machine component is most likely the cause?

Backlash in the lead screw or ball screw assembly

A dull cutting bit

Incorrect spindle speed

A worn spoilboard

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Explanation: Oversized circles (especially if consistently oversized in one axis) are a classic symptom of backlash. When the axis reverses direction during circular interpolation, the lost motion causes the cut to be slightly larger than programmed.

Which of the following is NOT a standard component of a CNC router's motion control system?

Pneumatic hammer

Motor driver

Controller board

Linear guide rails

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Explanation: A pneumatic hammer is not part of a CNC router's motion control system. The motion system consists of motors, drivers, a controller board, and linear guide systems (rails, bearings, screws) that work together to produce precise movement.

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Last Updated: 2026-03-19