Linear Axes

An axis represents a direction of movement. The standard cartesian axes in a 3-axis CNC machine are X, Y, and Z. These axes guide the movement of the cutting tool or workpiece in a three-dimensional space.

As seen to the right, the X and Y axes (red and green respectively) typically control the horizontal shifting of the workpiece, enabling it to move left, right, back, and forth at a constant height. Meanwhile, the Z axis (blue) is responsible for the vertical travel of the spindle, allowing it to move up and down.

In some machines, an additional axis, often referred to as a 4th-axis or A-axis, incorporates the rotation of the workpiece, enabling a wider variety of design to be manufactured. This additonal mode is covered in future content.

Workpiece (Stock)

The workpiece (or stock) is the raw material from which the design is made. It must have geometry that can be securely attached to the CNC bed, a process known as fixturing or workpiece hold-down.

Common methods for securing stock include using a vice, chuck or fixturing tables. More strategies pertinent to this badge and the machines accessible to you are covered in future content.

Fixturing table

The fixturing table, or machine bed, is the rigid base on which the machining takes place. It provides a flat, stable reference surface. It typically contains T-slots or threaded holes by which a work holding device (a vice for example) can be installed to hold stock securely for machining.

Depending on the style of machine, the table is mechanically aligned to the machine’s linear motion, meaning its surface is parallel to the X and/or Y planes of motion. So typically, in order to move the tool around the stock, the entire bed moves.

Air Supply

Many CNC machines, including all of ours, need compressed air to operate certain functions. As seen in the examples to the right, many CNCs have plumbed compressed air aimed at the cutting end to help evacuate chips and to cool the tool and material.

In more complex CNCs such as those covered in CNC Milling Intermediate, tool changers and coolant mist accessories both rely on an external air supply.

Tool and Tool Holder

The tool (the cutting bit) is the business end of the CNC Mill. It rotates and it's sharp edges make direct contact with the stock, removing material to mill, drill or shape the design. We will cover the differences in tooling in the next module.

Typically, a unique segmented clamping system called a collet secures the cutting tool to the tool holder. A collet is effectively a spring that clamps evenly around a tool when tightened.

Automatic Tool Changer (ATC):

Some CNC mills are equipped with an Automatic Tool Changer (ATC), which allows the machine to automatically switch beween tools without operator intervention. When a machnining operation requires a different tool, the machine executes a sequence to return the current tool and retireve the next one from the tool carousel or magazine.

This reduces operator involvement, machining efficieny and enabkes more complex multi tool operaitons to run unattended (if you have confidence).

It is important to note that a CNC machine does not understand what is being manufactured. It grimly executes your motion commands, then sits motionless until it’s time to execute again. In summary, the machine is dumb, and so it’s vital the instructions given to the machine are carefully considered. But how do we communicate to the machine where to cut and where not to cut? Where to start and where to end?

This is where coordinate principles and machine offsets come into play!

A coordinate system consists of a cartesian origin (X=0, Y=0, Z=0) with axes. The Machine Coordinate System (MCS) is the 3-dimensional volume the machine can move within. Imagine a cube with an origin point in a corner as seen the image to the right, the CNC head can move a relative distance into the volume from this origin point and is constrained to move within this volume (the cube).

A Work Coordinate System (WCS) is a user-defined reference point that lives within the volume of the MCS (as seen in blue). The WCS origin has a specific offset (distance) away from the MCS origin.

The WCS is what is defined within the CAM software. As the user we state that all movement cutting is defined from a specific origin point, our WCS, giving us a way to communicate positions to the machine. As you gain more experience, we'll discuss why carefully considering the location of your WCS is important.