2 vs. 3 Axis Machining – CNC Profiling

Traditional 2-axis milling remains common on CNC machines, but adding a third axis greatly expands machining possibilities. It can make previously impractical parts possible and may reduce cycle times.

Two-Axis and Three-Axis Machining

Most modern CNC mills can accept and execute 3-axis programs. Both 2-axis and 3-axis machines use the X, Y, and Z axes; the distinction is whether the third axis participates in the cutting motion used to profile the part.

In 2-axis milling, the X and Y axes can move simultaneously while machining an internal or external profile. With 3-axis machining, the tool can also follow profiles involving coordinated XZ or YZ movement, such as a curved or waving surface contour.

Selecting a Machining Plane

When writing a program by hand, the following G-codes select the active machining plane:

• G17: XY plane
• G18: XZ plane
• G19: YZ plane

Aside from selecting the appropriate plane, programming is similar to other G-code programs.

YZ-Plane Example

To select the YZ plane, use absolute positioning, set inch units, and then command a positive Z move with a negative Y move:

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

G1 Y-.5 Z2.23 — make a linear feed move to Y −0.5 and Z 2.23.

To return to the conventional XY plane, issue G17.

Verify New Programs

Use CNC simulation or toolpath-rendering software to verify a new program, especially when coordinated 3-axis machining is unfamiliar. Confirm the selected plane, coordinate system, units, clearances, and tool motion before running the program on a machine.

Practical machine time and careful experimentation are essential for building proficiency with multi-axis profiling.