Introduction to 4th Axis
4th Axis
Some CNC machines can be extended to utilize 4th axis capabilities. Typically,
a machine that cuts using a rotary table and tailstock uses a rotary axis as its 4th
axis. Any machine with 4th axis capabilities greatly increases its potential work
range for applications such as carving, scanning and indexing.
Indexing is the simplest function to use on a 4th axis. Indexing is utilized for
applications when multiple operations are required on several different sides of a
workpiece. In these cases, the axis is usually defined as the A-axis. Within a G-
Code file, X-, Y- and Z-commands are provided for the machine's three axes. At
certain points in the file, rotary commands or “A” commands are given to index or
rotate the part into a new position. A good example between each pocketing
operation to rotate the part at regular intervals, typically 90°.
Another type of 4th axis application is sometimes called an axis swap. A tool
path for a flat part is generated with the intent of carving it on a cylindrical
surface. This is done by swapping the X- or Y-axis for the rotary axis. Thus, the
original X-axis of the flat part is now going to be carved around the workpiece in
the rotary table. This is the equivalent of wrapping the tool path around a part
instead of along the X- or Y-axis.
The last 4th axis application is what is referred to as true 4th axis machining.
Tool paths are generated using all 4-axis commands: X, Y, Z and A. This utilizes
the full potential of the rotary table and allows the machine to create the part in
the most efficient and flexible way. There are, in fact, several parts that cannot
be made by swapping, but require true 4th axis machining.
Some CNC machines can be extended to utilize 4th axis capabilities. Typically,
a machine that cuts using a rotary table and tailstock uses a rotary axis as its 4th
axis. Any machine with 4th axis capabilities greatly increases its potential work
range for applications such as carving, scanning and indexing.
Indexing is the simplest function to use on a 4th axis. Indexing is utilized for
applications when multiple operations are required on several different sides of a
workpiece. In these cases, the axis is usually defined as the A-axis. Within a G-
Code file, X-, Y- and Z-commands are provided for the machine's three axes. At
certain points in the file, rotary commands or “A” commands are given to index or
rotate the part into a new position. A good example between each pocketing
operation to rotate the part at regular intervals, typically 90°.
Another type of 4th axis application is sometimes called an axis swap. A tool
path for a flat part is generated with the intent of carving it on a cylindrical
surface. This is done by swapping the X- or Y-axis for the rotary axis. Thus, the
original X-axis of the flat part is now going to be carved around the workpiece in
the rotary table. This is the equivalent of wrapping the tool path around a part
instead of along the X- or Y-axis.
The last 4th axis application is what is referred to as true 4th axis machining.
Tool paths are generated using all 4-axis commands: X, Y, Z and A. This utilizes
the full potential of the rotary table and allows the machine to create the part in
the most efficient and flexible way. There are, in fact, several parts that cannot
be made by swapping, but require true 4th axis machining.
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