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CNC milling is a computer-controlled machining process used to remove material from a solid block (known as stock) to create a desired shape or component. It is one of the most widely used manufacturing methods in engineering, prototyping, and product development.
CNC stands for Computer Numerical Control, where pre-programmed digital instructions guide the movement of cutting tools. These instructions are typically generated from CAD (Computer-Aided Design) models and translated into machine-readable code using CAM (Computer-Aided Manufacturing) software.
Unlike manual machining, CNC milling offers:
CNC milling is part of subtractive manufacturing, meaning material is removed to form a part. This differs from additive methods like 3D printing, where material is built layer by layer.
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An axis represents a direction of movement within the CNC machine. In standard 3-axis milling, these are the X, Y, and Z axes, enabling precise motion in three-dimensional space.
The X and Y axes position the workpiece, while the Z axis controls the spindle movement. Together, they enable accurate and repeatable machining.
The spindle is the motor that drives the cutting tool, rotating it at high speeds to remove material.
At UNSW Canberra Makerspace, CNC milling is performed using the RoboDrill, a high-speed machining centre capable of precise cutting and rapid tool changes.
Selecting the correct spindle speed is important for:
The workpiece, or stock, is the raw material used to create the final part.
Before machining, it must be:
This process, known as fixturing, is essential for safety and accuracy.
Common methods include:
Proper fixturing prevents movement during machining, ensuring dimensional accuracy and avoiding tool damage.
The tool turret is a rotating unit that holds multiple cutting tools in fixed positions. It enables automatic tool changes during machining, allowing different operations (turning, drilling, boring) to be performed without stopping the machine.
The chuck is a clamping device mounted on the spindle that securely holds and rotates the workpiece during machining.
Proper clamping is essential to prevent vibration, inaccuracy, or workpiece movement.
The main drive motor powers the spindle, providing the required speed and torque for cutting operations.
It directly affects machining performance and efficiency.
Guideways are precision rails that guide the movement of machine components such as the carriage and tailstock.
They are critical for achieving consistent machining accuracy.
The tailstock is a movable component located opposite the headstock that supports long workpieces during machining.
It is essential when machining long or slender parts.
The controller is the central computer system that operates the CNC machine. It acts as the user interface, allowing operators to load programs, set parameters, and control machine functions.
On machines like the RoboDrill, the controller enables precise, automated machining while giving the operator full control over the process.
The flood coolant pump delivers a continuous flow of coolant directly to the cutting area. It plays a critical role in maintaining machining performance and tool life.
This system is commonly used when machining metals and some plastics where heat generation is significant.
Compressed air is required for various CNC machine functions. It supports both operational and auxiliary systems within the machine.
A stable air supply is essential for reliable machine operation and consistent performance.
The coolant mister uses compressed air to deliver a fine mist of coolant to the cutting area. It provides a lighter alternative to flood cooling.
This system is often used for lighter machining operations or when full flood coolant is not required.
The tool holder is the component that secures the cutting tool to the spindle. It ensures the tool is held firmly and accurately during machining.
At UNSW Canberra Makerspace, CNC machines use air-assisted tool holders, allowing quick and safe tool changes with pre-set tools. This improves efficiency and reduces setup time.
The cutting tool, held by the tool holder, makes direct contact with the workpiece to remove material and shape the final component.
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CNC machines operate using a coordinate system, and machine offsets are used to define the exact positions of the tool and workpiece within that system. Without offsets, the machine would not know where to start or how to position itself accurately.
There are two main types of offsets used in CNC milling:
Work Offset (Work Coordinate System)
Tool Offset
Before running a job, both work and tool offsets must be set correctly. This ensures:
Proper understanding and setup of machine offsets are essential for reliable and precise CNC machining.
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Selecting the correct material is essential for CNC milling. Different materials behave differently during machining, affecting cutting performance, tool wear, and final surface finish.
CNC milling machines can be used to machine a variety of materials, including:
Each material requires appropriate cutting speeds, tooling, and cooling methods to achieve optimal results.
When selecting a material, consider the following:
Understanding these factors helps ensure safe operation and high-quality outcomes.
Some materials are not suitable for CNC machining due to safety and equipment risks:
Note: If you are unsure about a material, always consult the Makerspace staff before use.
