2 vs. 3 Axis Machining – CNC Profiling

Traditional two-axis milling on a CNC machine remains common, but adding another axis greatly expands machining possibilities. It can enable parts that may not be practical with two-axis programming and may also reduce cycle times.

Two-Axis and Three-Axis Machining

Most CNC mills have X, Y, and Z axes and can run programs that use three-axis machining. The distinction concerns how those axes are used during cutting.

In two-axis milling, the machine can move simultaneously along the X and Y axes while cutting the outside or inside profile of a part. Using a third axis makes it possible to combine X- and Z-axis movements to machine features such as a wavy contour. Y- and Z-axis profiling is also possible by changing the active programming plane.

Selecting a Machining Plane

When writing a CNC program manually, the active machining plane is selected with these G-code commands:

• G17 selects the XY plane.
• G18 selects the XZ plane.
• G19 selects the YZ plane.

Otherwise, the programming approach is similar to other G-code programs. For example, the following commands select absolute positioning, inch units, and the YZ plane before making a linear move in positive Z and negative Y:

G90 G20 G19 — select absolute positioning, inch units, and the YZ plane.

G1 Y-.5 Z2.23 — make the programmed linear move.

To return to the conventional XY plane, issue a G17 command.

Verify New Programs

Use rendering, backplotting, or CNC simulation software to verify a new program, especially when three-axis machining is unfamiliar. Simulation helps identify programming mistakes before the program is run on the machine. Practical machine time and careful experimentation are valuable for developing proficiency.