4th Axis Interfacing

4-axis milling involves the same processes involved in 3-axis machining, where a cutting tool is used to remove material from a piece to create the desired shape and profile. However, in the case of 4-axis machining, milling is performed on an additional axis. A 4-axis CNC machine operates on the X, Y and Z axes like a 3-axis machine, but it also includes rotation around the X-axis, which is called the A-axis. This is the 4th axis that’s added to our machining process. In most cases, the workpiece will be rotated to allow for cutting to occur around the B-axis.

4-axis milling is useful when holes and cut-outs need to be made in the side of a piece or around a cylinder. They can provide quick and efficient work based on computer numerical inputs for precise results.

A "normal" CNC or manual milling machine has three axes (the majority of these are vertical machining centres or manual mills) the x, you and Z axis. Normally if you stand in front of the machine the x-axis is left to right, the y-axis is front to back and the Z-axis is up and down. Although many machines have a bed (remember, with those T slots) that's moving. However if you program the machines or move them by hand, assume that the bed and therefore your product is standing still. It is your cutter that's moving.

On a 3 axis VMC we can for example mill slots, drill holes and face of the part, the cutter stays in a vertical direction. Now, if we add a fourth axis it usually rotates around the x-axis (that's the left-right direction) and therefore we can also make holes and slots in the front and back of our products.

Because we can rotate our cutter around the part. Again, in theory, the product still isn't moving. So we rotate our cutter around the x-axis and therefore the new axis it's called an A axis. Now, we're not satisfied yet because we also want holes and slots in the sides of our products, so let's add another axis of rotation. And now it gets a little more tricky. When our A-axis is at zero, our fifth axis is perpendicular to our Z axis, because the cutter is vertical again. This may look silly to have a rotating axis around an axis that's rotating (the spindle).