Essential CNC Machine Concepts and Technical Specifications

Posted on Jan 31, 2026 in Electromechanical Engineering

CNC Machine Specifications and Capacity

The specification of a CNC machine gives detailed information about the capacity, size, accuracy, and performance of the machine.

Important CNC Machine Specifications

  1. Machine Type – CNC lathe, CNC milling machine, CNC machining center
  2. Table Size – Length × width of worktable
  3. Maximum Workpiece Size
  4. Spindle Speed Range – Minimum and maximum RPM
  5. Feed Rate – Rapid and cutting feed
  6. Number of Axes – 2-axis, 3-axis, 4-axis, 5-axis
  7. Tool Capacity – Number of tools in tool magazine
  8. Positioning Accuracy
  9. Repeatability
  10. Control System Used – FANUC, Siemens, Mitsubishi, etc.
  11. Power Requirement
  12. Coolant System Type

Coordinate Systems in CNC Machining

CNC machines use a coordinate system to locate the tool position accurately.

Coordinate Axes

  • X-axis: Horizontal movement
  • Y-axis: Vertical movement
  • Z-axis: Depth or spindle movement

Coordinate Systems

  1. Machine Coordinate System (MCS)
    • Fixed reference of the machine
    • Zero point decided by the manufacturer
  2. Work Coordinate System (WCS)
    • Zero point set by the operator on the workpiece
    • Common codes: G54, G55, G56

Programming Methods

  • Absolute Positioning (G90) – Measured from the origin
  • Incremental Positioning (G91) – Measured from the previous point

Spindle Speed (RPM) Calculation and Importance

The spindle speed controls the cutting speed of the tool.

Formula

The spindle speed (RPM) is calculated using the following formula:

Spindle Speed (RPM) = (1000 × V) / (π × D)

Where:

  • V = Cutting speed (m/min)
  • D = Tool diameter (mm)

Importance of Spindle Speed

  • High RPM leads to a better surface finish.
  • Low RPM is used for heavy cutting.
  • Correct RPM reduces tool wear.

Machine Control Unit (MCU): The CNC Brain

The Machine Control Unit (MCU) is the brain of the CNC machine.

Main Functions

  1. Reads CNC program (G & M codes)
  2. Controls axis movement
  3. Controls spindle speed and feed rate
  4. Sends signals to servo motors
  5. Monitors alarms and safety
  6. Controls tool change

Major Components

  • Input devices (keyboard, USB)
  • CPU
  • Display unit
  • Memory
  • Servo control system
  • Feedback devices (encoders)

Cooling Systems in CNC Machines

The cooling system removes heat generated during machining.

Functions of the Cooling System

  • Reduces tool temperature
  • Improves surface finish
  • Increases tool life
  • Removes chips from the cutting area

Types of Cooling Systems

  1. Flood Coolant System
  2. Mist Cooling System
  3. Through-Tool Coolant System

Common Coolants

  • Water-based emulsions
  • Cutting oils
  • Synthetic coolants

Selecting CNC Machine Control Systems

Selection of the control system depends on specific machining needs.

Selection Criteria

  1. Type of Machine (lathe, milling, machining center)
  2. Number of Axes Required
  3. Complexity of Machining
  4. Required Accuracy and Speed
  5. Ease of Programming
  6. Availability of Service and Spares
  7. Compatibility with CAD/CAM
  8. Cost of Control System

Common CNC Control Systems

  • FANUC
  • Siemens
  • Mitsubishi
  • Heidenhain

Short Answers for CNC Certification (Viva Prep)

These questions and answers are useful for oral examinations (Viva).

Q1. What is CNC?

CNC stands for Computer Numerical Control, used to control machine tools using programs.

Q2. What is MCU?

MCU is the Machine Control Unit that controls all machine operations.

Q3. What is WCS?

The Work Coordinate System (WCS) is the reference set by the operator on the workpiece.