A 4 Axis Mill adds an additional rotary axis. Compared to the 3 axis mill which is a more simple VMC, a 4th axis mill allows rotation on the X-axis. Many brands carry 4 Axis CNC machines like Haas, Laguna, Hardinge and others.
A normal CNC milling machine has three axes: the X, Y and Z axis. From the front of a machine, the X-axis is left to right, the Y is front to back and the Z is up and down. The workpiece is stationary on a bed and the cutter does all the moving (unless there is a T-slot bed).
3 Axis CNC Mill | 4 Axis CNC Mill | 5 Axis CNC Mill |
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This configuration can mill slots, drill holes and face off parts with the cutter in the vertical direction only. | Generally, the 4th axis rotates around the X-axis (which moves left to right). This allows you to make holes and slots in the front and back of the workpiece. The cutter can rotate around the part which is fixed on a table. The fourth axis is called the A axis. | When the A axis is at zero, a fifth axis would be perpendicular to the Z axis. The cutter can be rotated 90 degrees towards to the front of the machine and moved to allow for milling around the sides of the workpiece. The 5th axis is called the C axis. |
The complexity of parts that can be made in one setup increases as the number of axes increase.
When deciding on the type of used 4 axis mills to purchase, key factors to consider will be part complexity, part mix and the average number of parts to be run per setup.