"One Perfect Part at a Time"

Machining in the 4th Dimension

The fourth dimension is often mentioned in science fiction as a dimension beyond the human senses. Today, real scientists (if there are such people) claim the fourth dimension does exist. But there are IMHO plenty of pseudoscience, especially promoted as video “entertainment.”  Material for a future rant…

In machining there really IS a fourth dimension. Usually called the 4thaxis. The Hobbyist Machine Shop (THMS) has a fourth axis for use on the Taig micro mill. It’s been on both the mill used for metal machining as well as the wax milling machine. Currently it is on the Taig micro-mill used for wax carving

THMS has (owns) four software CAM software packages that can create g-code for the 4thaxis machining. I’ll list them but will not (here) get into the fine details of using them.

Two types of 4thaxis operations are most common.

First is indexing. The material to be machined is held in the 4thaxis rotational device. Standard X, Y, Z three axis machining is performed on the surface facing the Z axis. 3 axis machining is paused, and Z axis is raised to clear all dimensions of the material. The 4thaxis rotates (indexes) the material to another face. This can be 180, or 90, or 45, or any equal or non-equal rotation. Then 3 axis machining operation resumes on the new surface plain presented. Repeat as necessary.

The second process (A axis rotation) requires setting Z axis Y position perpendicular to the center rotational axis and A axis assumes the movements of the Y motion vectors by rotating. Where A axis was stationary in the first method, the actual Y axis is stationary in the second. I call it 3.5 axis machining as it is not full four axis movement. In CAD it’s called “unwrapping the A axis” and presenting it as a flat plain surface, output as either X or (usual) the Y axis.

It must be noted that this works for A substituting for either X or Y axis direction, dependent on how the A axis is configured on the milling machine. The post processor makes this adjustment in my system.

These two separate modes of operation are the most common, especially for the hobbyist. But certainly, both methods can be combined in a hybrid milling operation. Such as machining an irregular 3D shape with A axis rotation, then milling a non-radial pocket or through hole into the shaped surface, using X, Y, Z milling and A axis indexing.

The fourth axis operation is fun to use at THMS. Perhaps because it is unusual. I call it 3.5 axis machining at THMS because only 3 simultaneous moves are occurring. Certainly, there is an application for full 4 axis movement. I don’t possess the software that can produce that movement, but it is possible. The THMS CNC control hardware can move 4 axis at the same time. Industrial grade “pro” systems can use 4, 5 and even 6 axis movement. Far beyond the realm of this meager THMS workshop.

However, the only limitation is imagination and writing the proper code to make it happen. A big pile of spendable money helps too.

*At this writing, FUSION 360 can create 4th axis G-code. But it is not full 3D. It is 2.5D and/or X, Y, Z + indexing. 3D-4thaxis is under development.


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